GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on January 07, 2017, 03:10:45 PM
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I have a couple of other projects to finish up, but I wanted to give you a tease about a new project I am about to start.... I have been collecting the parts for nearly a year.... It all started when Travis at W.A.R. was moving his shop and decided to "clean house" and send me a big box of parts.... When I opened my "surprise package" I was pretty enthused with the contents, and could see a lot of the parts required to build two Bottled Marauders.... I scraped together enough money to buy the remaining parts I didn't plan on making myself, and the results of this collecting of bits and pieces is shown below....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Wood_zps8eiv2h5q.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Wood_zps8eiv2h5q.jpg.html)
Above are the parts for a Traditional rifle, using the beautiful stock that Travis supplied.... He also sent me two main tubes, a drop down, and a ton of other parts, including a bunch of valves, one of which (shown) I modded by moving the seat forward and increasing the ports to 7/32" (0.219").... I purchased two receivers from Crosman (through Lloyd Sikes), along with the Gen 1 MRod trigger group.... Below are the parts for the Tactical version.... I purchased another drop down from Travis, the PRod trigger group through Lloyd, and he graciously supplied me with the AR style Buttstock to help this project along.... The valve is a Cothran Powerhouse, which will be used in one of the builds....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Tactical_zpslexalosh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Tactical_zpslexalosh.jpg.html)
Below is a photo of the tank options I have available.... At the rear is a 500 cc, 250 bar (3625 psi) tank from England, next a regulated 3000 psi 500 cc from Travis, and in the front another 500 cc 3000 psi, but with an adapter to fit directly to the drop down, so that it can be used unregulated.... Travis also supplied me with an adapter for the Metric 250 bar tank as well....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tank%20Options_zpsu118i1w5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tank%20Options_zpsu118i1w5.jpg.html)
I haven't completely decided on the calibers yet, I have several barrels to choose from.... I have a .25 cal LW Polygonal, a .30 cal TJ's, a .308 PB barrel, and a .357 cal TJ's.... I have obtained some 1/2" ID high-modulas Carbon Fibre tubing with a 0.64" OD.... Sleeving the TJ's liners with that would increase the stiffness to at least equal to a steel barrel with a 5/8" OD (the diameter of my other barrels).... and I have determined that I can bore the front of the MRod receivers out to that size forward of the two 4/40 mounting screws.... which will allow me at least 2 diameters of support for the larger barrel inside the receiver for a very rigid, free-floated barrel installation....
All the parts will be interchangeable.... I plan to end up with two receiver/barrel assemblies, which can mount on either main tube.... One tube will contain my modded MRod valve, with suitable hammer, spring, and SSG.... while the other will contain the Cothran valve, with the optimum parts for that.... and both will have their own drop down, a complete, ready to go, pressure assembly, minus tank.... Any of the three tanks can be used on either main tube.... Onto each main tube, I will be able to attach whichever trigger assembly and stock I wish.... I will be making a rear mount for the AR stock that will contain the SSG, of course....
Anyway, that's what my next major project is.... I hope you enjoy following along as it progresses.... My thanks to Travis, Lloyd, and Don for their assistance and generosity....
Bob
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Wow... looks good already. I'll definitely be following your build on these. I've been eyeing the tactical look with a front tank lately.
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Bob with an M-rod based bottle gun (2) .... His disco stuff may be getting dusty
Be watching this one too !
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Nice looking collection of parts Bob. Any idea where Travis got that wood stock from ?
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Nope, no idea.... I think it's a Bullpup stock, but I'll be using it conventionally, since BP stocks are prohibited in Canada.... I've already inletted it for the MRod trigger in a conventional (rifle) setup....
Bob
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Bob, I have been interested in Bottle Rod Mod's for quite some time as a big fan of the Rapid and AirWolf AG's. Yet is seem the idea comes and goes rapidly often. Wish it would become an easier option
As one poster on another form used as his sig.
I'd rather have a bottle in front of me, than a frontal lobotomy. 8) LOL
Wishing you very good fitting and finishing on your project Bob! ;)
Knife
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I think the big problem is that guys don't want to pay for the time necessary to make the drop down tank block.... I've been making my own for years for my 22XX/Disco conversions, and have given the drawings to several machinists.... They inevitably would have to charge too much for what people perceive them to be worth to make any money.... The only one currently available (that I am aware of) is from JDS, and I would not use it because of the way it mounts into the MRod tube.... Travis has stated he will do another run of them if he gets 5 orders, but even that doesn't seem to be happening....
http://airgunguild.com/pcp-c02-and-helium-powered-airguns/bottled-mrod-kits-buyers-list-order (http://airgunguild.com/pcp-c02-and-helium-powered-airguns/bottled-mrod-kits-buyers-list-order)!-deadline-is-january-9-2017/
You would need the drop down and tube, as they thread together.... and that comes to $235 just for those two parts.... bottle, and regulator or adapter, extra....
Bob
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Bob
I have a bottled kit from Travis that I have been following Lloyd build of the 30 cal Mrod for Don and just paid for my plenum for the huma reg so I can start the build as soon as I get it and the TSS from Travis. Its in a RAI stock with the AR butt stock with Daves adjustable adapter. I will be following this build as well very closely as I get the parts to start my build. I am hoping to be able to shoot the JSB 33.95 pellets at 950fps or so to be good an accurate 100 yard gun. I also have a Jim Gaska MM barrel in the breech now so the plenum and TSS are the last two parts I need to proceeded with a finished gun.
Mike
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Sounds like you have a pretty good handle on it, Mike.... I haven't even calculated the plenum volume in Travis' BRod kit yet.... *LOL*.... but having the regulator on the bottle will at least make all of the tube volume into plenum.... I sure wish the Cothran valve would produce a bell-curve.... I'm not crazy about setting it up unregulated in a "first shot fastest" scenario.... so that may restrict its use to a regulated gun.... The plenum volume will then dictate the most suitable caliber.... So far it's just a collection of parts without a clear direction to pursue....
Bob
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Mine is going to be pretty close to the one Lloyd is building for Don except it will be 25 cal and have a 500cc bottle instead of the tube extension. So if Lloyds calculations for the total plenum volume is correct it should be close to 44ccs. I am using the cothran valve with a Hill gauge block that is much more open than a stock one and likely close to the hogged out one Lloyd is using with the BT65 30 cal plenum on the huma reg. I wish the drop down block was threaded to accept a paintball reg but its not and use the same bushing as the bottom bottle in your pictures so I plan to drill out the small pass thru hole in the bushing out to 5/16 or 3/8" for a better flow into the tube. I am hoping the larger plenum will clear the threaded bushing once assembled into the drop down block since with the stock 25 cal huma reg its real close to the end of the drop down when its fully threaded into the short tube.
I will know soon since the last two pieces will be here this next week.
Mike
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The drop down block Travis makes DOES fit paintball regs.... The adapters he sells are exactly the same thread (1/2"-NPS).... What is different is that the regulator doesn't seal down inside the threads in a smoothly bored hole.... You use an O-ring between the bonnet OD and the drop down.... outboard of the thread, just like with the adapter.... REALLY a slick arrangement.... and much easier to machine.... 8)
Bob
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The drop down block Travis makes DOES fit paintball regs.... The adapters he sells are exactly the same thread (1/2"-NPS).... What is different is that the regulator doesn't seal down inside the threads in a smoothly bored hole.... You use an O-ring between the bonnet OD and the drop down.... outboard of the thread, just like with the adapter.... REALLY a slick arrangement.... and much easier to machine.... 8)
Bob
Thanks Buddy, if you need anything just PM me and Ill look threw boxes.
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Thanks, Travis, but you've
cost me enough done enough for me already.... ;D
Bob
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Thanks, Travis, but you've cost me enough done enough for me already.... ;D
Bob
LOL
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I got around to measuring the plenum volume in the tubes today.... There is 69 cc between the back of the tank block and the front of the valve.... However, in my drilled out MRod valve there is another 4 cc (even more in the Cothran), and in the tank block, which has large passages, there is about another 8 cc.... so the total is over 80 cc.... That means the plenum is large enough for any .25 cal or for a .30 cal pellet shooter for sure.... and for a .257 cal or .30 cal bullet shooter, or .35 cal pellet shooter it is large enough that it would only take about another 100 psi bump in the setpoint to make up for any lack in plenum volume.... It is, however, on the small side for a .308 or .357 bullet shooter, or anything over about 160 FPE, so for those an unregulated setup would be indicated.... The good news is that the passages through the tank block, and the brass tank adapters, are large enough that without the regulator in between, the entire 500cc tank becomes part of the reservoir, able to keep the pressure up during the shot.... This means the effective reservoir is about 580 cc (35 CI) when unregulated....
Bob
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Dang I need to regulate my .30 Brod. Definitely going to bottle my .25 now as well.
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The drop down block Travis makes DOES fit paintball regs.... The adapters he sells are exactly the same thread (1/2"-NPS).... What is different is that the regulator doesn't seal down inside the threads in a smoothly bored hole.... You use an O-ring between the bonnet OD and the drop down.... outboard of the thread, just like with the adapter.... REALLY a slick arrangement.... and much easier to machine.... 8)
Bob
Bob
I just checked the threads and you are correct that they do fit the ninja regs threads and the bottle accepts the regs threaded end as well. I never even thought to check the fit so thank you very much since I now don't need the huma reg and bigger plenum if I choose to go with the reg on the bottle instead. It just never occurred to me to check the threads. So I see you use the o ring between the adapter block and ninja regs bonnet but I assume then you need to remove the check ball or pin in the top of the bonnet since there is no pin in the end of the adapter to depress the check ball or pin in the bonnet. I agree its a slick trick that in much easier to machine and will give the added plenum size to achieve the power level and fps I want out of my Brod.
Also in using the cothran valve I will be using a 26 gram MDS with aluminum insert form Motorhead in place of the stock hammer to help lessen the hammer strike on the cothran valve. I believe its going to turn out very nice now and better and easier than I first anticipated. Again thank you for letting me know that the block will accept the ninja regs so easy.
Mike
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Yes you have to remove the check valve inside the bonnet of the regulator.... It's nice that Travis made the passages through the drop down so large so that if you use it unregulated the bottle can flow fully into the plenum.... that adds a touch of volume to the plenum, too....
Bob
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Well the bushing I have has a 1/8" hole thru it so it will need opened up to 5/16 or 3/8" to match the passage thru the tank block which is no big deal. This opens up a bunch of new possibilities for the build with the different combinations possible with the bottle and regs. I am now thinking of getting a CF 4500 psi bottle to have even more air to gain more shots per fill and reduce some weight as well.
Mike
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You wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....
Bob
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Nice looking collection of parts Bob. Any idea where Travis got that wood stock from ?
The stock looks exactly like my Kam P-12, (previous to MrodAir) I doubt if SPA has changed the stock. The only difference is the through hole for the the trigger guard. I don't know if Bob has already modified that possibly?
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You wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....
Bob
Bob
I had not thought about the 4500 psi with a reg that fails sending the full pressure into the tube so you make a very good point indeed. I was planning on using the ninja style reg in the bottle so I would have the largest plenum space to obtain the best power versus volume available. Yea it would be real good if they had burst discs at even 4000k but 3800k would be better so I may look into trying to find one closer to the safety limit of the tubes rating.
I know the bottle I bought from Travis when I got the full kit he stated it was safe to fill to 3500 psi so if I did use a higher PSI bottle and the reg failed I would definitely replace at a minimum the valve screws and any other piece that looks marginable with an inspection. This is some very good info to ponder as I start my build.
One thing I have thought about as well is with the check valve out of the ninja reg it will not be possible to remove the bottle from the tank block since gun will stay pressurized at al times. I was thinking of using a on/off valve in between the reg and tank block so the bottle would not have to be degassed completely for service. What are your thoughts on it use to allow service of the gun.
Mike
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While it's nice to be able to "in theory" remove a regulator/bottle assembly from a PCP, in practice you are VERY likely to blow the O-rings on the end of the reg. because once the reg. is unscrewed, you still have pressure in the reservoir in the gun.... Some tank blocks (eg. the QB79) have a vent hole to bleed off the CO2 left in the gun when you start unscrewing a CO2 tank, and at those pressures, you don't usually ruin the O-ring.... However, it has been my experience that unscrewing an HPA regulator from a QB tank block will blow the O-ring as it tries to extrude it through the small vent hole.... In addition, it can be quite hard to even turn the reg. if there is still pressure in the gun.... which in itself should warn you that there is still pressure there.... If you continue, and if there is no vent hole (there isn't in Travis' blocks), you could be injured or killed when the reg., with bottle attached, clears the gun which still has pressure in side.... and not a small amount, but 80 cc.... enough to do a LOT of damage....
I think it is therefore safer to have to bleed down all the air before removing the bottle.... Yes, you could install an on-off valve between the reg. and drop down, so that you could remove the bottle (with reg. and valve) while filled, but you still have to bleed all the air from the gun before unscrewing the on-off from the drop down....
Bob
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While it's nice to be able to "in theory" remove a regulator/bottle assembly from a PCP, in practice you are VERY likely to blow the O-rings on the end of the reg. because once the reg. is unscrewed, you still have pressure in the reservoir in the gun.... Some tank blocks (eg. the QB79) have a vent hole to bleed off the CO2 left in the gun when you start unscrewing a CO2 tank, and at those pressures, you don't usually ruin the O-ring.... However, it has been my experience that unscrewing an HPA regulator from a QB tank block will blow the O-ring as it tries to extrude it through the small vent hole.... In addition, it can be quite hard to even turn the reg. if there is still pressure in the gun.... which in itself should warn you that there is still pressure there.... If you continue, and if there is no vent hole (there isn't in Travis' blocks), you could be injured or killed when the reg., with bottle attached, clears the gun which still has pressure in side.... and not a small amount, but 80 cc.... enough to do a LOT of damage....
I think it is therefore safer to have to bleed down all the air before removing the bottle.... Yes, you could install an on-off valve between the reg. and drop down, so that you could remove the bottle (with reg. and valve) while filled, but you still have to bleed all the air from the gun before unscrewing the on-off from the drop down....
Bob
Bob
With the on/off valve I would turn the valve off then shoot the gun down to exhaust the pressure inside the gun so there would be only the pressure in the tank that is contained with the valve in the off position. I most definitely would not try to unscrew the tank without a on/off valve to prevent the pressure from blowing the bottle off when unscrewed whether its a QB or Brod.
Mike
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You wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....
Bob
Bob
I had not thought about the 4500 psi with a reg that fails sending the full pressure into the tube so you make a very good point indeed. I was planning on using the ninja style reg in the bottle so I would have the largest plenum space to obtain the best power versus volume available. Yea it would be real good if they had burst discs at even 4000k but 3800k would be better so I may look into trying to find one closer to the safety limit of the tubes rating.
I know the bottle I bought from Travis when I got the full kit he stated it was safe to fill to 3500 psi so if I did use a higher PSI bottle and the reg failed I would definitely replace at a minimum the valve screws and any other piece that looks marginable with an inspection. This is some very good info to ponder as I start my build.
One thing I have thought about as well is with the check valve out of the ninja reg it will not be possible to remove the bottle from the tank block since gun will stay pressurized at al times. I was thinking of using a on/off valve in between the reg and tank block so the bottle would not have to be degassed completely for service. What are your thoughts on it use to allow service of the gun.
Mike
Mike,
Why not just use a 3K disc on the output side of your Ninja? Plenty of them around as they are used on Co2 tanks. Then if the reg fails you will not get any higher then 3K in the gun.
Rob
Yea that would work since the regs pressure would be likely no more than 2400 max and likely far less with a 80cc plenum it would not need to be set to high for the power I plan to make with the Brod.
Mike
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As Rob pointed out, if your setpoint is low enough, a 3K burst disc will work fine.... that is what I have installed in my regulator, because it is currently set for 2000 psi, and won't likely be set much higher, because I am using a 3000 psi tank, and there would not be enough headroom.... One of the uses of a 4500 psi tank would be to use a regulator set to 3000-3600 psi, in order to be able to take advantage of the Cothran valve in a much higher powered setup.... That was why I was saying it would be nice if we could get a 3800 psi burst disc....
One more thought.... are the ON-OFF valves made for CO2 pressures, or are they intended and safe at 3000 psi (or 4500?)....
Bob
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As Rob pointed out, if your setpoint is low enough, a 3K burst disc will work fine.... that is what I have installed in my regulator, because it is currently set for 2000 psi, and won't likely be set much higher, because I am using a 3000 psi tank, and there would not be enough headroom.... One of the uses of a 4500 psi tank would be to use a regulator set to 3000-3600 psi, in order to be able to take advantage of the Cothran valve in a much higher powered setup.... That was why I was saying it would be nice if we could get a 3800 psi burst disc....
One more thought.... are the ON-OFF valves made for CO2 pressures, or are they intended and safe at 3000 psi (or 4500?)....
Bob
Bob
I am not after big power in my build so the 3k burst disc would be perfect for my application. I see how the 4500 psi tank could be beneficial for a much higher reg set point but my interest is for higher shot count by having more high pressure air available to increase the number of shots above the reg set pressure. I will not need over 2400 psi max and more likely 2000 will be more than enough with the 80cc plenum that the tube and tank block will have available since if I can make 80 fpe for the top end of the power range I will be very happy. My goal is JSB 33.95s at 950 fps for 68 fpe or there abouts so will just determine that when I find the most accurate fps for shooting out to 100yards.
I had not got that far into looking at on/off valves to know if they are rated for 3000 to 4500 psi air pressure versus the 1900 max of CO2 on/off valves. So one more thing to consider and research. Just the fact that the ninja reg will fit the tank block and tank has opened up all new ways to build my Brod that I have some decisions to iron out.
I am glad you contribute so much to this forum and to the members in the projects we take on since you are another very objective and qualified view to help guide us here. I myself will always be appreciative of the contributions you provide me.
Mike
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Mike, the 250 and 300 bar CF bottles, and the 250 bar aluminum one I have from England, are all 18mm x 1.5mm thread, which is larger than the Ninja regs, not smaller, they are 5/8"-18 NF.... You can get an adapter from Travis for the Metric bottles, and as Rob says, you can get Metric thread regs from China and then put Ninja guts in them.... Fortunately, all the regs. are the same on the output side, 1/2"-14 NPS....
I don't know if you remember, but I recently tested a Cothran valve in my Disco Double, with a .25 cal barrel, starting at 1900 psi in this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.40 (http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.40) .... If you check out Reply #49, you will see a chart of velocities at various pressures with the 34 gr. JSB Heavies, and also the 50.6 gr. BBTs.... With the 34 gr., it only took 1700 psi to get 958 fps at 1.04 FPE/CI.... That was with a 25" barrel and bore-size porting to match the 1/4" exhaust port on the Cothran valve.... There is no reason the MRod Cothran won't perform the same, at the same pressure, so your only variables should be barrel length and port size.... Using the same efficiency, and a 500 cc, 3000 psi tank, you should get about 40 shots at 70 FPE.... With a 4500 psi tank, regulated at the same 1700 psi, that would more than double.... 8)
How long is your .25 cal barrel?....
Bob
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Mike, the 250 and 300 bar CF bottles, and the 250 bar aluminum one I have from England, are all 18mm x 1.5mm thread, which is larger than the Ninja regs, not smaller, they are 5/8"-18 NF.... You can get an adapter from Travis for the Metric bottles, and as Rob says, you can get Metric thread regs from China and then put Ninja guts in them.... Fortunately, all the regs. are the same on the output side, 1/2"-14 NPS....
I don't know if you remember, but I recently tested a Cothran valve in my Disco Double, with a .25 cal barrel, starting at 1900 psi in this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.40 (http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.40) .... If you check out Reply #49, you will see a chart of velocities at various pressures with the 34 gr. JSB Heavies, and also the 50.6 gr. BBTs.... With the 34 gr., it only took 1700 psi to get 958 fps at 1.04 FPE/CI.... That was with a 25" barrel and bore-size porting to match the 1/4" exhaust port on the Cothran valve.... There is no reason the MRod Cothran won't perform the same, at the same pressure, so your only variables should be barrel length and port size.... Using the same efficiency, and a 500 cc, 3000 psi tank, you should get about 40 shots at 70 FPE.... With a 4500 psi tank, regulated at the same 1700 psi, that would more than double.... 8)
How long is your .25 cal barrel?....
Bob
Bob and Rob
I am aware the threads on the ninja regs are 5/8-18 NF but did not know the 250 and 300 bar bottles are the bigger metric thread of 18mmX 1.5mm so to use the 250 or 300 bottles I would have to swap the guts from the ninja regs into the metric regs for them to work. I can do that if the guts are the same since I have a metric 3000 psi bottle that I just ordered a Chinese reg for to be able use it. I have also seen the CF bottles from china and was curious if they are a safe quality bottles that both of you would recommend to use for a lighter weight replacement for an aluminum bottle. The prices are much more reasonable than ones you buy here and suspect the one here may be from china as well but not sure so want to be sure they are safe since they show to be certified for build quality.
Bob
I did follow your cothran disco build and is partly what I am basing my goal from the Brod on but was going to go back and read thru to refresh me on the reg pressure and other aspects that I will need to use to build the Brod. I am using a MM 20 inch hammer forged barrel in the build so its 5 inches shorter than your disco and was going to use a .1875 TP port out of the cothran valve all the way into the barrel. So I may have to raise the reg set pressure closer to 2000 psi to make up for the smaller Port. I will be happy with 40 shots per fill but doubling that would be even better. Lots of things to think about and test to get the best overall efficiency and power.
Mike
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Bob and Rob
I am aware the threads on the ninja regs are 5/8-18 NF but did not know the 250 and 300 bar bottles are the bigger metric thread of 18mmX 1.5mm so to use the 250 or 300 bottles I would have to swap the guts from the ninja regs into the metric regs for them to work. I can do that if the guts are the same since I have a metric 3000 psi bottle that I just ordered a Chinese reg for to be able use it. I have also seen the CF bottles from china and was curious if they are a safe quality bottles that both of you would recommend to use for a lighter weight replacement for an aluminum bottle. The prices are much more reasonable than ones you buy here and suspect the one here may be from china as well but not sure so want to be sure they are safe since they show to be certified for build quality.
Bob
I did follow your cothran disco build and is partly what I am basing my goal from the Brod on but was going to go back and read thru to refresh me on the reg pressure and other aspects that I will need to use to build the Brod. I am using a MM 20 inch hammer forged barrel in the build so its 5 inches shorter than your disco and was going to use a .1875 TP port out of the cothran valve all the way into the barrel. So I may have to raise the reg set pressure closer to 2000 psi to make up for the smaller Port. I will be happy with 40 shots per fill but doubling that would be even better. Lots of things to think about and test to get the best overall efficiency and power.
Mike
From all of my research (internet and hands-on) the 3K and 4500 reg differ only in the lettering on them. All of the internal parts seem to function exactly the same when interchanged. Did you also get a Ninja piston kit to use with the 3K bottle? If not just ask Travis about the differences. I think you find the $14 well spent.
About the CF bottles - just make sure which ever one you get it is DOT approved, otherwise no Hydro Testing facility will certify them......at least none I have talked to.
Rob
No I did not get a ninja piston kit with my bottle from Travis if that's the one you are referring to the kit from him was the AR style stock , tank block, short tube, tank bushing to connect tank to block and assorted hardware. There was no regulator in the kit and I was not aware the ninja regs would fit the bottle and block till Bob informed me that they will fit. I have also seen the piston kits on ebay for 12 bucks.
The CF bottles from china the I looked at did have the Dot cert on the label so no issue there and I have a fire extinguisher buddy that does my hydros so I don't think it will be an issue either way.
Mike
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^X2, good advice, Rob, particularly on making sure your CF bottle is DOT approved.... BTW, Travis sells 250 bar, 500 cc DOT Approved CF Bottles, as used on the FLEX....
I just set up Lloyd's spreadsheet using the numbers from my .25 cal DD with the Cothran valve, to see what your changes might do to the required setpoint pressure.... My setup gave 958 fps @ 1700 psi with a 135 cc plenum and a 25" barrel, with 34 gr. JSBs....
Changing from my 135 cc plenum down to 80 cc should drop the velocity at 1700 psi to 946 fps.... which would only require a 50 psi increase to compensate (1750 psi)....
Changing from a 25" barrel to 20" should drop the velocity at 1700 psi to 913 fps.... and would require an increase to 1900 psi to get back to 962 fps....
The two changes together should give you 951 fps @ 1900 psi.... assuming the MRod and Disco Cothran valve perform equally (they should)....
Lloyd's spreadsheet isn't designed to look after altering port sizes (that's coming).... but I have a rough correction that I apply.... When I do that, starting with the 80cc plenum and 20" barrel at 1700 psi.... changing from 1/4", bore-size porting down to 3/16" could drop the velocity to 871 fps @ 1900 psi.... and require an increase to 2300 psi to get back to 951 fps....
From those calculations, the plenum you can almost ignore, and you can compensate for the 20" barrel without too much problem.... but the "small" ports will really cost you in performance.... These are just predictions, but you might have a look at using larger ports to flow enough air for the 34 gr. pellets without having to use a setpoint over 2000 psi....
Bob
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^X2, good advice, Rob, particularly on making sure your CF bottle is DOT approved.... BTW, Travis sells 250 bar, 500 cc DOT Approved CF Bottles, as used on the FLEX....
I just set up Lloyd's spreadsheet using the numbers from my .25 cal DD with the Cothran valve, to see what your changes might do to the required setpoint pressure.... My setup gave 958 fps @ 1700 psi with a 135 cc plenum and a 25" barrel, with 34 gr. JSBs....
Changing from my 135 cc plenum down to 80 cc should drop the velocity at 1700 psi to 946 fps.... which would only require a 50 psi increase to compensate (1750 psi)....
Changing from a 25" barrel to 20" should drop the velocity at 1700 psi to 913 fps.... and would require an increase to 1900 psi to get back to 962 fps....
The two changes together should give you 951 fps @ 1900 psi.... assuming the MRod and Disco Cothran valve perform equally (they should)....
Lloyd's spreadsheet isn't designed to look after altering port sizes (that's coming).... but I have a rough correction that I apply.... When I do that, starting with the 80cc plenum and 20" barrel at 1700 psi.... changing from 1/4", bore-size porting down to 3/16" could drop the velocity to 871 fps @ 1900 psi.... and require an increase to 2300 psi to get back to 951 fps....
From those calculations, the plenum you can almost ignore, and you can compensate for the 20" barrel without too much problem.... but the "small" ports will really cost you in performance.... These are just predictions, but you might have a look at using larger ports to flow enough air for the 34 gr. pellets without having to use a setpoint over 2000 psi....
Bob
Bob
Thanks for the calculations and I was thinking the small ports may be the choke point so may have to think about opening them to the 1/4" you used in the disco to reach the goal I am after. The port from the valve and TP would be easy to use 1/4" ice maker tube or some of the peek I got from Motorhead and I assume to get the barrel to the same flow as the 1/4" ports it would need to have the hole elongated to prevent the pellets from snagging on the hole when loading.
I at least now know the parameters I need to use to get to the power level I am after.
Thanks very much Bob for figuring this out for me since without your math I would be going by trial and error till I got to where I want to be if I did at all.
Mike
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If you read through the DD Powerhouse valve thread, is gives the barrel port dimensions to equal 1/4" diameter exhaust and transfer ports.... IIRC, it was 3/16" wide by 5/16" long.... I used a 3/8" OD transfer port to match up with the Cothran valve, so you have to drill the tube and receiver to match that, and mill a 3/8" flat on the barrel (minimum depth).... I used a piece of 3/8" OD Teflon rod, drilled with a size "F" drill (0.257") for the TP, to match the Cothran exhaust port.... The transition from round to oblong was made within the barrel wall itself....
Bob
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I worked on the tubes today.... The tubes that Travis sent me are intended for Gen 2 MRod parts.... I have two Gen 2 receivers, but I wanted to be able to interchange the tubes from traditional wood stocked rifle to a tactical setup with pistol grip.... Since that needed a PRod trigger group, and it is the same bolt pattern as the Gen 1 trigger, I had to redrill the tubes to accept the Gen 1 and PRod triggers.... In addition, the transfer port hole in the top of the tube had to be drilled out to 3/8" to accept the larger transfer ports.... Here are the redrilled tubes, with the new holes circled....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Drilled%20Tubes_zpscginj7my.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Drilled%20Tubes_zpscginj7my.jpg.html)
The front two holes on the bottom are drilled and tapped with 8-32 threads, while the rear hole on the bottom is the clearance size for an 8-32 (11/64"), because the rear trigger screw threads into the rear tube plug.... A custom rear plug will be required because the bolt pattern is Gen 1 on the bottom and Gen 2 on the top, to accept the two rear 4-40 screws that hold down the receiver.... The only change on the top was drilling the original TP hole out to 3/8" in the same location....
I installed the male Foster and gauge in the tank blocks (drop downs), along with a 1/4"-NPT flush plug on the bottom.... I want to be able to tether the guns without having to waste all the air to fill the 500 cc bottles during development, so I made a blanking plug for the tank/regulator mount in the drop down from an old regulator bonnet....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tank%20Block%20and%20Plug_zpsoz964m1a.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tank%20Block%20and%20Plug_zpsoz964m1a.jpg.html)
I simply removed the pin valve and drilled and tapped the bonnet for a 1/8"-NPT flush plug to seal it.... I installed a couple of 5/8" long 10-32 SHCSs in the threaded holes in the bonnet and screwed them in until they touched each other in the middle.... This gives me something to grip better with my fingers to screw the blanking plug into the front of the tank block.... You can see the O-ring that seals the regulator bonnet to the tank block sitting on the bonnet.... It seals in the recess in the front of the tank block, instead of way down inside, so you don't use an O-ring in the normal location on the bonnet.... Travis is to complimented on this arrangement, it certainly is a lot easier to machine, and less prone to leaks, IMO.... I then installed the valves in the tubes, and threaded in the drop downs, stopping with them pointing downwards, lined up with the trigger group.... Once there is pressure inside, they won't have any tendency to rotate, and it isn't important for them to be screwed up tight against the end of the tube (and it you do, they won't line up with the trigger on the bottom of the tube.... You simply screw them in all the way and then back them out until they line up with the trigger.... I then installed my blanking plug and checked for leaks.... Here is the assembly, which I will leave overnight to make sure it holds pressure....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Assembled%20Tube_zpsjwln6ifp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Assembled%20Tube_zpsjwln6ifp.jpg.html)
For the eagle-eyed amongst you, you will notice that the gauge is showing over 3000 psi.... I filled the tube to 3000 psi exactly with a known gauge, but this one shows 3500.... In fact, it was 500 psi high all the way from the start of the fill.... Does anyone know if that is an MRod gauge?.... Anyway, it's nice to get a start on this project, other than just collecting parts for it....
Bob
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I wish i ad your skills!! I modified my QB78 deluxe myself and ad to REDUE the cut and drilling twice even with the carton templet that another member has posted long time ago.. I dont mind INVESTING MONEY in a rifle that i got the results i want.. Your build are awesome and i just feel LUCKY you shared this with us.. Thanks for your generosity..
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If you read through the DD Powerhouse valve thread, is gives the barrel port dimensions to equal 1/4" diameter exhaust and transfer ports.... IIRC, it was 3/16" wide by 5/16" long.... I used a 3/8" OD transfer port to match up with the Cothran valve, so you have to drill the tube and receiver to match that, and mill a 3/8" flat on the barrel (minimum depth).... I used a piece of 3/8" OD Teflon rod, drilled with a size "F" drill (0.257") for the TP, to match the Cothran exhaust port.... The transition from round to oblong was made within the barrel wall itself....
Bob
Bob
Got it and again thanks for the help in working it all out for me so all I have to do is the actual work to build the gun. The rest of my parts will be here tomorrow and Thursday so next week I hope to start on it.
Mike
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Bob
Yes that appears to be a Gen II gauge since its the same as the one from my Gen II 25 but apparently has been damaged so it reads 500 Psi high. I have three Mrods with two being GenI and one Gen II and all the gauges read within 100 psi of my big liquid filled gauge on my bottle and the shoebox fill station.
Mike
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rstern!! Can you tell me the advantages of bottling the gun or doing something like double tubing would be more stiff construction...
I know you have more than one rifle with bottle and i know the power mods you make to them called for more volume.. But what the advantages of bottling over double tubing or increasing tube size like the FT model??
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The bottle I am using is 500 cc, plus the 80 cc in the plenum gives a total air on board of 580 cc.... A stock MRod is 215 cc, so this is 2.7 times the air.... Even if you used a second tube of the same diameter as the original, you could only double the volume. leaving the bottle with 1/3 more air.... The reservoir portion of the MRod tube (just the part between the fill fitting and the gauge block), which is 15" long, weighs 1.5 lbs., and a second reservoir of the same volume, with the extra ~3" of length needed for end plugs, and the end plugs themselves, would weigh about 2 lbs.... for a total of 3.75lbs. for 430 cc.... The bottle I have (aluminum, not CF) weighs 1.75 lbs., to which you have to add the tank block and 4.75" of tubing for the reservoir (the weight of the rest of the tubing is the same as in an MRod), which is about 1 lb., for a total of 2.75 lbs.... so the bottle setup is 1 lb. lighter for 33% more air....
If you regulate, the gains in usable air volume are even greater.... You have to add the weight of the regulator to both guns (similar), but to get an 80 cc plenum like I have, and install the regulator (~ 20 cc) inside the upper tube, which you would do in a regulated MRod, you would lose about 100 cc, bringing the HPA reservoir down to just 115 cc, or 330 cc on a double tube setup.... Compare that to the 500 cc bottle (upstream of the regulator), and you have 1 lb. less weight and over 50% more air for the bottle gun, compared to a regulated double tube MRod with two identical tubes.... I don't think the stiffness of the reservoirs is an issue, because most would free float the barrel anyway....
Using a single, larger diameter tube instead of two smaller tubes, does NOT save any weight, if you stay with the same material.... The tube itself, in order to have the same MSWP and safety margin, must increase in thickness in proportion to its diameter, so the weight of metal to encompass a given volume actually stays the same.... If you continue that larger diameter back to encompass the action, then you have more weight for the single tube design.... Yes, you can use titanium tubing instead of steel for the tubes, but you can also use a Carbon Fibre bottle instead of aluminum.... Both will save a lot of weight, but of course are much more expensive....
Bob
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I started working on the receivers today.... On most of my projects I have to make them from scratch, but for this project I started with two .25 cal MRod receivers and bolts.... The first thing to be done was to drill out the transfer port hole to 3/8" OD, the same diameter as the Cothran valve, and the holes I drilled in the tubes to match.... I plan to use a piece of 3/8" OD Teflon rod, drilled as appropriate, for the transfer port.... So, I set one receiver up on my milling attachment on my lathe, using a stop at one end to minimize the setup on the other one, centered off the existing transfer port hole, and drilled it out to 3/8".... I then took it out of the vice on the milling attachment, put the other one in, checked the hole center, and drilled it as well....
I had decided to drill the front of both receivers to 5/8" for about 1-3/8" deep, staying in front of the two 4-40 screw holes, so that the full diameter part of the barrel will be held rigidly in the receiver.... It doesn't do a lot of good to have a 5/8" barrel and then turn it down to 1/2", all it will do is flap around (bend) where the receiver starts.... I planned on using my 4-jaw chuck, holding the back of the receiver, and drilling the front with a 5/8" drill in the tailstock, but I found that the receiver is VERY flexible where it is machined away for the magazine, so much so I was afraid that it would not run true, and if the drill grabbed, it might bend and destroy the receiver, so I needed another plan.... I chucked a piece of 1/2" cold-rolled steel in the chuck, which was a perfect slide fit in the front hole of the stock receiver.... I then mounted the receiver in my milling attachment vice so that the steel rod rotated and slid back and forth freely, so that insured that the chuck was lined up with the barrel hole in the receiver.... I then simply drilled the hole out with a 5/8" drill to a depth of 1.4" to the shoulder of the drill.... The LW barrel is actually 16mm, which is a few thou over 5/8", and it slid perfectly into the drilled hole.... I drilled the other receiver the same way, and it turns out that the CF tubing I have is also 16mm OD, so it also fits nicely into the new, larger hole in the front of the receivers.... Here is what they look like now....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Modded%20Receiver_zpsz7a18rkv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Modded%20Receiver_zpsz7a18rkv.jpg.html)
I then checked to make sure that the stamped end of the LW barrel was, indeed, the breech, by measuring the land diameter with my new small hole gauges.... I found out that the land diameter at the breech is 0.247" and at the muzzle it is 0.244", so the barrel has a 0.003" choke.... I machined the breech down to 1/2" OD for 1.5" of length, and checked how it fit into the receiver.... With an O-ring against the shoulder of the barrel, sitting against the drilled shoulder in the receiver, the back of the barrel was about 0.010" too far back for the magazine to slide into place, which I left for now.... I then used a chambering reamer I made several years ago for the LW barrel on my Hayabusa, and machined the chamber and leade to the required depth so that the front of the chamber is just ahead of where the front of the barrel port would be located.... I checked what a bullet and pellet looked like chambered to that depth, and was pleased with the results, so carried on with the next step, which was laying out the barrel port....
I carefully measured the location of the port from where the back of the barrel needed to be to fit against the locating hollow in the magazine, added a 0.010" (because I knew I had some extra length available), set the barrel up in my milling attachment, carefully centered it relative to the chuck, and drilled and milled the barrel port and the 3/8" diameter flat for the transfer port to seal against.... The port transitions from a 1/4" diameter at the TP spot face to 3/16" wide by 5/16" long at the bore line, so I actually can use up to a bore size transfer port should it be required.... After the milling, I touched up the port with a small ball in my Dremel, blending the 1/4" round port into the oblong barrel port, within the thickness of the barrel itself.... I then slid the barrel into the receiver, lined up the transfer port spot face with the hole in the receiver, and tried the magazine.... As expected, the barrel needed to be shortened 0.010" for the magazine to slide into place....
The last step on machining the back of the barrel was to machine the internal O-ring groove to seal the bolt.... If anyone else attempts this build, the location of that groove is CRITICAL.... The groove is 0.070" wide to fit the O-ring, and from the back of the TP spot face to the back of the barrel is only 0.125", so there is only 0.055" of material left TOTAL for BOTH sides of the groove.... The force on the O-ring from air pressure, is backwards, so I left more material there, 0.035", which only leaves 0.020" between the front of the O-ring groove and the back of the TP spot face.... and YES they would intersect if you put the groove too far forward in the barrel.... Anyway, knowing that was an issue, I was careful and all went well, the bolt slides nicely through the O-ring, and the barrel now looks like this....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20LW%20Barrel_zpsvzx97xja.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20LW%20Barrel_zpsvzx97xja.jpg.html)
I assembled all the parts so far, just so that I could have a look, and take a photo so that you can see the progress, and the proportions....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Sub%20Assembly_zps5srvmbcg.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Sub%20Assembly_zps5srvmbcg.jpg.html)
I'm very pleased with the progress to date, so I guess it's time to make the hammers and rear plug and SSG next....
Bob
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Dang that looks good!!
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That looks really nice, Bob!
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Very familiar work going on there .... measure 3 times & cut once.
Bob, your not wasting any time getting into this project !!! ... Looking great so far ;)
Curious to see what you do for Hammer & SSG type / design ???
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Im trying to talk him into a MDS hammer on The Guild, I think he needs your source as McMaster wont ship to canada
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Im trying to talk him into a MDS hammer on The Guild, I think he needs your source as McMaster wont ship to canada
Tell me it's not so ... Lol ;D
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The plan today was to get started on the hammers, but I decided instead to finish off the barrel and receiver.... I marked the locations for the spot faces for the setscrews on the top of the barrel and drilled those.... I installed the bolt and discovered I was missing parts yet again (that's what happens your first time playing with parts from a gun you have never worked on before).... I had to make the small plate that prevents the bolt from over-rotating yet allows the handle to be left or right.... no big deal, just time.... Fortunately I still had some small 2-56 screws left over from my R/C Yacht days to install it.... Once I installed the cocking pin in the bolt I could check the position of the shoulder on the bolt and the length of the probe, and the shoulder was too far forward and the probe too short.... I had heard that the bolt was hardened, so I heated the front cherry red and let it cool slowly, but it was still too hard to drill for a new probe.... I figured it might be just case-hardened, so I ground the tip off the bolt, and sure enough that allowed me to get a bite with a small drill....
Mounting the bolt straight in the lathe chuck was tricky because of the handle and the short mounting surface around that, which is the only place to grab it.... I came up with a neat trick to hold it straight while I tightened the chuck up.... I held the bolt probe in the tailstock Jacob's chuck to hold the end of the bolt centered, ran the handle end into the 3-jaw until the handle touched the chuck face, between two of the jaws, and then tightened the chuck good and tight.... When I undid the tailstock chuck and backed it away and mounted a tiny center drill, it was perfectly centered on the end of the probe where I had ground away the case hardened surface.... I drilled a small center hole, and the changed to a 3/32" drill and drilled in about 3/4".... I then removed the bolt from the chuck and ground the probe off, back to the tapered shoulder, and ground the tapered portion off to get through the case hardening there as well.... Of course since I had previously drilled a hole for the new probe, I had a center hole so that I could use a 60* center in the tailstock and line up the bolt again in the 3-jaw in the headstock.... I checked that it was running straight (it was), and then faced off the shouldered portion of the bolt square.... I checked it for length, and decided I would just put a very slight conical taper on the face from the OD to the probe hole.... This puts the edge of the shoulder flush with the back of the barrel port.... I then used a piece of 3/32" drill shank, glued it into the hole in the bolt, and then cut it to length for the new probe.... I made the probe long enough to seat JSB Kings with the skirt flush with the front of the barrel port.... That puts the King Heavies about 1/16" further forward, because they have a shallower hollow in the base, and a cast bullet would sit with the base 1/8" ahead of the front of the barrel port.... You can see what the probe looks like in the photo below....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/006%201024x336_zpsonxogrvz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/006%201024x336_zpsonxogrvz.jpg.html)
I calculated the remaining area for airflow around the probe, and it works out to the same as a 15/64" transfer port.... I will likely be using a 7/32" port, which is the same size as the exhaust port in my modded Mrod valve (0.219"), so unless I have to go to full area porting should offer no restriction to the flow.... If I do have to use full 1/4" ports, I may have to change to a flat nosed bolt that retracts into a J-slot to allow maximum flow.... but I don't anticipate it, as I'm not trying to build a 100 FPE quarterbore....
At the muzzle I wanted to mount a Hatsan Air Stripper, as I happened to have a spare .25 cal on hand.... This required turning the barrel and threading it 1/2"-20 NF for the stripper.... I found a position in my 3-jaw where the bore ran true, and then faced the muzzle off square to the bore, and then turned the barrel OD down to 0.50" for a length of 0.80" and threaded it.... The photo below shows the installation....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Completed%20Receiver%20and%20Bolt_zpsnesa28ei.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Completed%20Receiver%20and%20Bolt_zpsnesa28ei.jpg.html)
Anyway, I think the upper assembly for the .25 cal version is now complete, and I can get on with the hammer and spring arrangement....
Bob
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I got a chance this afternoon to make the hammers.... I turned them from 1144 Steel.... They are 1.20" long, drilled 0.50" to a depth of 1.00" to the drill shoulder, and weigh 104 grams each.... There is just enough room in the cocking slot to go from contacting the back of the modded valve I made (which was shortened 0.075") to just cocking the trigger, for a total hammer stroke of 0.88" with my valve.... and about 3/4" with the Cothran valve.... With the deeper recess for the spring I have 2.75" of length from the shoulder in the hole to the back of the tube.... This means I can use a 3" spring for my SSG without having to make the rear plug stick out more than 1" behind the tube or so.... I'm pleased with the way they came out....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/104%20gr%20Hammers_zpsrp3eapok.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/104%20gr%20Hammers_zpsrp3eapok.jpg.html)
You may wonder why I am always using heavy hammers with maximum stroke in my builds.... Most of the time I'm going for a lot of FPE with a heavy bullet, and that means I need a large valve throat and lots of dwell.... The hammer energy to crack the valve and create lift comes from the spring and travel, but the hammer momentum to create more dwell comes from hammer weight.... A heavier hammer allows me to use a lighter spring, with a lower cocking force, and still get the FPE I want....
Bob
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TONS OF info will be revealed in this build too... LOL Good to know the Relationship betwen the force needed to crack open the valve and the weight of the striker.... Thanks Bob
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Looking good Bob! Those are going to be a pair of awesome rifles. Can't wait to see how they shoot.
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Its winter for sure its the only time Bob gets his builds going. Keep up the good work and looking forward to finished products.
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Today I made the first SSG.... I left all the parts longer than necessary until I find out if it will work properly throughout the range of tuning I need, I can always shorten them up and make them prettier later.... The reason I didn't make the second one at the same time is that the housing will incorporate a mount for my AR style stock....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/SSG%20Parts_zpsvpm6bkuk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/SSG%20Parts_zpsvpm6bkuk.jpg.html)
The housing is a piece of 1.25" OD 6061-T6 aluminum turned down to fit in the back of the main tube, with the appropriate tapped holes to secure it.... On the top are two 4-40 screws through the receiver on 0.688" centers, and on the bottom a single 8-32 hole that mounts the trigger group.... The front just clears the back of the hammer when it is all the way back.... It is drilled through and tapped 9/16"-18 NF for the gap adjusting bolt.... I know that is huge, but it allows the spring assembly to be withdrawn out the back without any other disassembly.... That is a feature I always like to employ on my RVAs and SSGs, it makes changes a breeze.... The gap adjusting bolt has a spring seat turned on the front end, to hold the spring in alignment.... The stop rod part of the spring guide is a 4.5" long piece of 3/16" drill rod, threaded 10-32 both ends.... At the back it has quite a bit of thread for preload adjustment, which is provided by the two nuts locked against each other.... There is a # 008 O-ring on the shaft to act as a cushion when the guide comes to a halt.... The front part of the guide is turned from a piece of aluminum rod....It is 0.48" OD at the front (the same as the spring) and profiled to fit the bottom of the hole in the hammer.... Behind that is a 1" long section that is 0.355" OD to act as a spring guide.... There is enough space between the two parts of the guide to allow for more preload and cocking distance than I need.... The spring I am using at the moment is 3" long (instead of the 2.5" used in a stock MRod), with a rate of 13 lb/in.... I have 0.40" of preload at the moment, which is about 5 lbs.... If I need more, I just wind the nuts down on the shaft.... If I need less, I can shorten the gap adjusting bolt (moving the rear spring seat back), but a better solution would be a weaker hammer spring.... I just don't have anything lighter at the moment....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/SSG%20Assembly_zpsyozslxl9.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/SSG%20Assembly_zpsyozslxl9.jpg.html)
In the photo above, the SSG is adjusted for zero gap with the current 0.40" of preload with my valve.... With the Cothran valve, where the end of the stem sits further back, the gap adjusting bolt would be further back.... I can shorten the back of the SSG housing to allow more adjustment if I have to increase the preload much.... I'm thinking I'm getting pretty close to being able to tether the version with my valve in it.... That will answer a lot of questions about the hammer spring requirement at various pressures.... The Cothran valve will require less hammer strike than mine, at any given pressure, so I could use a lighter spring, or just increase the gap.... My valve at 3000 psi will be the test of the maximum hammer strike required for these guns....
Bob
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Excuse my short memory Bob... I see this setup and i dont remember if it was asked in the ssg tread... Would a 1/4 to 3/8 piece of rc polytube could replace the 2 o-ring in the back... The détails and finish of making each of your milling is breath taking...I really like the race of that drilled bolt you got on the back.. It provides extra adjusting and possible extra strenght spring... Great job!!
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Id flute those hammers as to not cause any air pocket in front of said hammers or vent air tube at rear of valve to allow air to get out. I find fluting works better and has added affect of less surface drag on hammer to tube.
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Way to go Travis..
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Alain, there is only a single O-ring as a bumper at the back of the SSG rod, between the nuts and the adjusting bolt.... It just keeps the SSG from crashing metal-to-metal....
Travis, any air pressure between the hammer face and the valve simply vents out the sear slot and through the trigger.... It is possible, I suppose, that there could be a slight vacuum behind the hammer that slows it, but the hole for my SSG guide rod is a bit oversize.... I guess the only way to tell for sure would be to drill a vent hole in the rear plug or tube to see if it made any difference in the hammer strike.... I'm not saying that fluting the hammer is a bad thing, however, and I may take your advice on that....
I made the Teflon transfer port today and assembled the gun and fired it for the first time.... Tethered at 1900 psi, at zero gap on the SSG, the velocity was a bit low, so I increased the preload in two 0.10" stages from 0.40" to 0.60", at which point I was able to hit the velocity plateau at zero gap.... I then installed the action in the wooden stock.... It weighs right on 7 lbs. without the bottle.... I haven't done anything with the comb of the stock yet....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/First%20Assembly_zpsgjsuxhzz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/First%20Assembly_zpsgjsuxhzz.jpg.html)
I then tested the velocity with 25.4 gr. JSB Kings and 34.2 gr. JSB Heavies, adjusting the Gap from zero out until the velocity dropped below 600 fps.... and then went the other way, adding preload (negative gap) until the plateau was confirmed.... ie I knew what the maximum possible velocity was with this valve, and 0.219" ports, at 1900 psi.... Here are those results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Tethered%201900_zps63qwn61m.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Tethered%201900_zps63qwn61m.jpg.html)
As expected, adding any preload against the valve stem instantly increased the report.... I like to adjust the preload on my SSGs until I can reach the velocity plateau just as the gap goes to zero.... Any more preload and you are just making the gun harder to cock, and it means that you have to increase the gap to drop the velocity back down to the knee of the curve.... I want just a bit more power, I would like to be on the knee of the curve at about 950 fps with the 34 gr. Heavies, so with this valve I would need to increase the regulator setpoint slightly, I think 2000 psi should be about perfect.... However, before I make that decision, I want to test the other tube with the Cothran valve at the same pressure, to compare the results....
All in all, I'm delighted with the initial results.... With the SSG adjusted so that there is a tiny gap, I am at 944 fps (68 FPE) with the 34.2 gr. JSB Heavies, at only 1900 psi.... Moving the seat forward in the MRod valve so that I was able to achieve the 7/32" exhaust port was worth the effort....
Bob
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Nice work on everything. I know you use what's on hand, but I think it would look good with a telescoping type stock. Surprised the SSG rod is so long. I'm gonna make one soon, and figured it should be pretty long.
Again, just nice work on everything.
Steve
I copied a lot of the info, explanations and charts for later. Thanks Bob.
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The SSG can be reduced in length at least 1/2".... by shortening the gap adjusting bolt, the housing, and the sliding rod.... Beyond that, you have to go carefully, or you may run out of room for preload and gap adjustment.... I left mine overlength on purpose, because the Cothran valve will require the entire SSG to be further aft about 1/8", as I had shortened my modded valve 0.075 and the poppet is in a different place, due to the valve seat being moved forward.... I probably should have linked to those mods earlier in this thread, I just assumed most would remember them.... http://www.gatewaytoairguns.org/GTA/index.php?topic=111416. (http://www.gatewaytoairguns.org/GTA/index.php?topic=111416.)
Bob
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Is this your first Mrod based build Bob? How are you liking the trigger? I wish all my rifles had that trigger!
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Its coming together very good Bob and you hit a nice power level on the first test fire. I am following closely since your build is almost the exactly how I want mine to turn out or close to the level you have now.
I have been out of town this weekend but have all the parts needed to start the build now in my possession. It turns out I likely will not need the plenum from the BT65 .30 cal since my plan is to use a ninja reg in the bottle versus one in the tube. It will be used in another build at a later date.
Mike
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This is my first MRod build, but I have used the trigger in many other builds before, and love it....
Mike, your 20" barrel will require a bit more pressure, as we discussed before.... and as you realize, my valve has 0.219" ports, not the 0.187" you were contemplating.... My next test will be with the Cothran valve with a 1/4" transfer port to match it.... My barrel port is large enough, the restriction should then be the bolt probe in the chamber, which should give me the equivalent of a 15/64" (0.234") passage....
Bob
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This is my first MRod build, but I have used the trigger in many other builds before, and love it....
Mike, your 20" barrel will require a bit more pressure, as we discussed before.... and as you realize, my valve has 0.219" ports, not the 0.187" you were contemplating.... My next test will be with the Cothran valve with a 1/4" transfer port to match it.... My barrel port is large enough, the restriction should then be the bolt probe in the chamber, which should give me the equivalent of a 15/64" (0.234") passage....
Bob
Bob
Yes I am aware of the port size you are using and just deciding if I am going to go that big on mine or not and have a reg set at 2200 Psi now for if I do go that big. I may try with the .187 port to see just what it gives first and go from there. I am not sure I am comfortable elongating the port in the MM barrel I have if by chance I mess up it could be ruined and I would be out cash and it took four months just to get the barrel made as well.
Mike
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You can get the FPE you want with a 3/16" port.... the question is at what pressure....
Bob
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You can get the FPE you want with a 3/16" port.... the question is at what pressure....
Bob
Exactly and I am going to find out. Then decide which route I want to go.
Mike
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The story of todays post is.... NEVER BE AFRAID TO LEARN SOMETHING NEW.... or at least open your eyes to existing problems.... ::)
I am always careful to make sure that the area between the front of the hammer and the back of the valve can't get pressurized, either from the hammer movement itself, or from an air leak through the valve stem during firing.... If that happens, you can get (in the worst case instance of a leaky valve stem) a machine-gun action where the pressure partially recocks the hammer and fires the gun again.... until the reservoir is empty (yes, I've had that happen).... Travis suggested that I flute my hammers to prevent this, but I double checked, and the sear slot in the bottom of the tube vents into the trigger, and out through the bottom.... However, I haven't been paying enough attention to the BACK of the hammer, where a vacuum can build up and slow the hammer strike.... The only gun I ever vented there, on a suggestion from Scott (Motorhead), was my B-51.... WHY I haven't been looking for this problem in other guns I don't know.... complacency, I guess.... Well, that just bit me.... in spades....
While I was triple checking the space in front of the hammer this morning, I looked at the area behind it.... Yes, there is a rather large cocking slot, with a matching one in the receiver.... but guess what.... There is nowhere for the receiver to vent, other than past the bolt at the ends, in an MRod receiver, with the rear bolt.... I had noticed some large ES values yesterday when I had the SSG backed off with a large gap, and the lightbulb finally went on.... With an SSG (or SSS or TSS), the spring quits pushing the hammer before it gets to the valve stem, and it coasts the last part.... What if there is a vacuum behind the hammer?.... Yup, that will start slowing the hammer down before it gets to the valve.... In addition, that vacuum is unlikely to be 100% consistent, shot to shot, which could increase the ES.... and the more gap you have between the spring and hammer, the worse both might be.... Time to find out....
I set the SSG for 1.5 turns of gap, and shot an 8-shot string.... The average velocity was 811 fps, but the ES was huge, with shots going from 790-834 fps.... definitely not good.... I stripped the back of the gun apart, and machined two slots in the bottom of the rear plug (SSG housing), at about 4:30 and 7:30, in the section that inserts into the tube.... The slots were 3/16" wide and 1/8" deep, and continued back 3/16" behind the rear of the tube.... That is the equivalent area of a 1/4" hole through the rear plug to prevent any vacuum forming behind the hammer on firing.... Here is what you see with the action out of the stock....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Vent%20Slots_zps9frg6jrt.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Vent%20Slots_zps9frg6jrt.jpg.html)
There happens to be a slot in my stock at the location of the vents.... If that isn't the case with a different stock, a different vent design may be necessary.... Anyway, I assembled the back of the gun again, adjusted the SSG gap to the same, 1.5 turns out, and fired a 34 gr. JSB through the Chrony.... Instead of 811 fps, it was 956 fps.... WOW !!!.... Obviously the vacuum behind the hammer was a reality, I had moved up onto the velocity plateau.... I went through the process of documenting the velocity vs gap with the vented rear cap.... On the graph below, the dotted red line is the new data, with the vent.... while the solid red line is yesterday's data, without the vent....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Modded%20Valve%20Tethered_zps2rgf1wzp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Modded%20Valve%20Tethered_zps2rgf1wzp.jpg.html)
There are two important things to notice.... First, it takes a LOT more gap to get to the knee of the curve with the vents.... which means that without them, the vacuum behind the hammer was slowing it dramatically.... Secondly, the slope of the downslope part of the curve is a lot shallower.... It takes more gap to lose the same amount of velocity.... To drop from 944 fps down to 760 fps now takes a 3 turn increase in gap instead of two.... That makes sense, because the bigger the gap, in the unvented setup, the more the vacuum would reduce the hammer velocity.... There is absolutely NO doubt this gun needs the area behind the hammer vented....
Since I had dramatically increased the hammer strike at the same settings, I could now do two things.... I could reduce the preload on the spring, making the gun easier to cock.... I reduced the preload to my original 0.40" (which was not enough yesterday, with the vacuum), and shot the data shown by the purple line.... As you can see, the "knee" of the curve still requires 3 turns more gap, even though the preload on the spring is reduced from nearly 8 lbs. to just over 5.... Since the larger gap means the spring is not compressed as far (and starts at less preload as well), the maximum cocking force, when the gun is set just below the plateau, at 944 fps, has dropped from 19 lbs. down to just 15 lbs.... In fact, I could further reduce the preload if I wish, and that would allow me to decrease the gap, and the cocking force, even more....
These vents did one more thing for me.... They increased the available hammer strike to the point that I could now test the gun at 2900 psi.... I checked it with the 34 gr. JSB Heavies, and the results are shown as the black line on the graph above.... This was shot with the preload on the spring still at 0.40", and to get to the plateau I had to set a turn of negative gap (actual preload on the valve stem).... I didn't try it, but I am confident that by going back to the 0.60" preload I could operate at 2900 psi and hit the plateau with a small gap.... In any case, these results proved that this valve is capable of cranking out 90 FPE at 2900 psi with the 34 gr. Heavies.... I didn't have the proper sized 51 gr. BBTs for this barrel, the ones I had were sized to 0.250" (so they were likely leaking a bit in the bore).... but by cranking in some preload I managed to find the plateau for them as well.... I was able to hit 963 fps (105 FPE) at 2900 psi with those bullets.... I have ordered an NOE Mould for the 51 gr. BBTs in 0.253/0.255", and the sizing bushings for them.... so at some point in the future I can experiment with them....
In conclusion, I am extremely glad I vented the area behind the hammer to prevent the vacuum from slowing the hammer.... I am frankly shocked at how much hammer strike was lost because of that vacuum, and the horrible ES that it caused.... You can bet I'm going to have a long, hard look at all my Disco based guns.... There may be more consistency, and easier cocking, lurking amongst any of them.... ::)
Bob
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Outstanding find! No wonder why Travis has a vent hole on the TSS!!
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Crazy what a vent can do... Bob I'm really not understanding why a vacuum affects the hammer strike that much, but would it affect a qb79 running a SSS?
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I have a question about the SSG. You used aluminum on the front of the 4 1/2 inch rod. Won't that get beat up after a while? I was thinking it had to be steel, and I even wondered if it needed to be hardened.
Surprising how much the hammer strike was affected by vaccume. I have a regulated Disco that has more ES than I expected. I wondered if galling of the tube, or just that steel on steel is creating excess friction that is also inconsistent. I made a plastic wear band for a piston I made for a 1377 years ago. No metal to metal contact, no galling, no need for lubrication.
Nice that you hit 100FPE ;D
Steve
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Outstanding good work my friend! Keep at it Bob your almost there now.
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After writing the previous thread, I changed all the parts over to the tube with the Cothran Powerhouse valve in it.... This is the best way to compare it to my modded MRod valve, by tethering it at the same two pressures, 1900 psi and 2900 psi, and using the same pellets.... Here are the results.... The horizontal axis on this graph is the same as the one above for my valve, and I used the same colours for the 34.2 gr. JSB Heavies at the two different pressures.... In both cases, the SSG had the same 0.40" preload, and "Zero" is the point where there is just barely a gap in the SSG setup.... The end of the valve stem in my valve is further forward than that of the Cothran valve, so my setup has 0.88" of maximum hammer stroke, whereas with the Cothran valve it is only 0.79".... but that suits the two valves, because mine needs more hammer energy to open.... This means that the SSG has to be adjusted to a different point (about 1.5 turns further out) with the Cothran valve to end up with zero gap.... but zero on both graphs has the same meaning, minimum gap on the SSG....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Valve%20Tethered_zpsqkgeaher.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Valve%20Tethered_zpsqkgeaher.jpg.html)
You can see at once the huge difference in the response of the Cothran valve to the gap setting.... Basically this valve is either "ON" or "NOT".... It exhibits the typical "cliff" which we have seen in other tests of the Cothran valve.... The most efficient point to operate the Powerhouse valve is just above the point where it no longer opens properly and consistently.... This may only be a matter of one flat (1/6 turn) on the SSG gap adjuster.... I didn't explore the exact location of that point yet, all I was after was the maximum velocity available at the two test pressures, and the range of SSG gap where the cliff started.... Relative to zero gap, at 2900 psi the cliff was at about 2 turns out, compared to requiring actual preload with my valve.... at 1900 psi, the cliff was at about 4 turns out, fairly similar to where the knee was with my valve.... As expected, with the larger ports, the Cothran valve was able to produce a bit more power than my valve was.... Here are the maximum velocity and energy achieved with the two valves at the two test pressures, with the pellet and bullet tested....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Valve%20Comparison_zps8ljr0fdf.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Valve%20Comparison_zps8ljr0fdf.jpg.html)
The port size on my valve is 0.219".... The Cothran valve has a 0.257" exhaust port, I used a 0.250" transfer port, and the barrel port is equivalent in area, but there is a 3/32" diameter probe in the chamber.... This reduces the effective area to that of a 0.234" port.... so it doesn't hurt my valve, but probably handicaps the performance of the Cothran valve slightly.... However, the only way around that would be to just a probeless bolt with a flat face, that retracts flush with the back of the barrel port in the firing position.... This would require milling a "J-slot" in the MRod receiver for the bolt lockup and cocking pin to retract into.... Since I don't plan on using anything heavier than my 51 gr. BBT, and I can already push that to nearly 1000 fps, I simply don't need to bother making that modification to the receiver.... However, if you wanted to use an even heavier bullet, as you might if you fitted a .257 cal barrel, you would be well advised to take the trouble to use a probeless bolt arrangement to achieve full barrel size porting with the Cothran valve....
Bob
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I don't think the aluminum nose on the SSG will get beat up, but I guess time will tell.... There is no impact on firing, only when the hammer is thrown back by the closing of the valve.... and I made the shapes to match, so the area is quite large.... Motorhead actually put an O-ring in the front of his, not a bad idea.... I tried a vent on my recently built Regulated Disco Double this afternoon, and if only made about a 20 fps difference.... so obviously there were nearly enough leaks to get rid of the vacuum.... For those of you that may ask if "Gun XXX" needs a vent, I suggest you simply take a look.... I'm not about to pull apart every PCP I have just to tell you.... If I do find any that have a problem, you can be sure I will post about it in the PCP Gate....
Bob
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May i asked??? Do you think with your recent discovery and analisis that, any gun highly mod would BENEFIT of fluting the hammer???
It`s not to criticized or find a winner because at the end, we are all winner finding new path in power using in those guns...
I think even a rolled out of factory discovery would benefit hammer fluting..
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Fluting the hammer will guarantee that it can't pressurize the air in front, or leave a vacuum behind.... regardless of whether the tube is vented or not.... As far as the friction is concerned, it should be a wash.... If the coefficient of friction (materials and/or lubrication, and smoothness) is the same, it doesn't matter whether you have a small area or large.... Back to Physics 101, guys.... more area equals less pressure per unit area.... less contact area increases the pressure per unit area.... and the friction force should stay the same either way.... Now if the hammer cocks on firing, and puts more pressure on the area between the flutes, the friction could go up or down.... I don't think there is any benefit.... but it looks KEWL, and will insure no "air lock".... so no reason why not.... One flute down each side should do no harm, IMO.... or just machine the sides off flat, like the PRod/Challenger hammers.... on the left in the photo.... Ignore the O-rings, they were part of a bstaley experiment....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/IMG_3489_zps2956a716.jpg) (http://s378.photobucket.com/user/rsterne/media/Discovery/IMG_3489_zps2956a716.jpg.html)
Bob
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Thanks for the precision.. I will not touch my QB`s for sure but want to give a try to my 2240... I`m working on PIPING the valve directly on the gaz block for no leaks or fear of pressurizing the tube like before... I will show chony number as soon as i perform the change over..
Many thanks.
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??? Yea that air we move around when stationary parts get thrown by springs etc ... is one many have not paid attention too.
It is after all part of physics that cause and effect are always in flux altering set perceptions by other effects present escaping ones attention.
Kudos Bob .... fine tuning further while traveling down that bottomless rabbit hole we're all in ???
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Not sure I agree with this statement Bob In this situation anyway. "If the coefficient of friction (materials and/or lubrication, and smoothness) is the same, it doesn't matter whether you have a small area or large.... Back to Physics 101, guys.... more area equals less pressure per unit area.... less contact area increases the pressure per unit area.... and the friction force should stay the same either way..." This is only true if all forces are equal on all sides but we have gravity and spring torque here also. I flute the top and sides where Gravity Isnt affecting the hammer like it does on the bottom so having less surface area in areas of lower drag does reduce drag overall I learned this many years ago building High pressure pump stators for The Polaris factory race team. Anyway its working well for you and thats Awesome sauce. Keep rocking !!!
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Actually, the "area don't matter" is straight from any Physics text for a flat block sliding on a flat surface with gravity being the force pushing them together.... The area is not part of the equation, only the weight and the friction coefficient.... It doesn't apply if the surfaces are not smooth, however.... like a rubber tire on pavement.... If the hammer is a tight fit in the tube, then area would certainly make a difference because of the interference fit.... but they need to slide under their own weight.... Offcenter forces could mess it all up, too....
For most hammers, the bottom, where the sear contacts, can't have a flute.... and if there is a cocking pin on the top, there could be a reason not to have a flute there.... I see no reason not to cut away the sides, though, with one exception.... If you have a side handle on the hammer to cock it directly, the offset weight will cause it to skew in the tube on firing (and worse, on cocking).... so flutes should not be in the plane of the handle, or opposite it, IMO.... I say leave the surfaces alone where you know there will be contact points, and the rest.... cut 'em away if you don't need the weight.... Same goes for milling off the sides (ala MRod hammer), or turning a waist (like a 22XX Disco), if the trigger sear doesn't need a flat bottom on the hammer....
However, as you say, whatever works for you....
Bob
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Looks like you've got a couple of powerhouse .25's there Bob. Hope your accuracy is as good. I'm sure they will be hammers. keep us updated on the progress.
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Thats a nice find Bob, gets me thinking about couple of my guns too.
Nice builds by the way, the one with ar stock and crosman group looks lot like my first gun did, and I still like it a lot.
Marko
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Oh, only one of them will be a .25 cal.... the other will be either .30 or .357.... although if I had an extra .257 barrel with a 14" twist about 28" long, I would give serious consideration to using that with a regulator set around 3000 psi on my 250 bar bottle with the Cothran valve.... my own version of the WAR Hammer, just to light a fire under Travis.... ;)
Bob
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Haha you old goat you'll have to do better than that to ruffle my feathers LOL. Seriously though let's do the 257 with Dons valve so you can finally convince me to build one. I'm on the fence just need a push.
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Just a little push LOL
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Just a quick note on the PHYSICS... I dig my 30+ years book and it also says that once an object is in mouvement, there is a cosine math to apply for the resistance of gravity.. Since the object is moving 90 degree OFF gravity pressure, it would translate to only 30 pourcent of the initial pressure required to move the same object.. Just me saying. And if you were to shoot down with the same line of forces as the gravity, you would substract the aid of the gravity to move the object for the force required to move it..
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~taking a hefty swing at the fencepost with an axe~
TIMBER !!!!
Bob
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LOL
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I pulled my modded valve out of the tube today and bored out the exhaust port to 0.234", and drilled out the transfer port to that diameter as well.... I inspected the MRod poppet, and it has a nice shiny seat, just indented a few thou.... It is not showing any sign of extruding into the port, as I have seen happen with a 0.281" throat.... The throat in my current valve is 0.266", which I have also used before without issue at 3000 psi.... However, I don't want to go any larger.... Unless you change the poppet material, going larger on the port, or using more than 3000 psi, is just asking for trouble.... The throat (when you subtract the 1/8" stem), the exhaust port, the transfer port, the barrel port and the bore (when you subtract the 3/32" bolt probe) are now all the same area.... I consider this the maximum practical for a modded MRod valve, unless you change the poppet, and no point in doing that unless you also go to a probeless bolt....
The larger ports increased the maximum velocity at 1900 psi by 24 fps, from 956 to 980 fps.... Here is the comparison, before and after enlarging the ports....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20New%20Ports_zpssbgjfoiw.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20New%20Ports_zpssbgjfoiw.jpg.html)
I want the ability to achieve 950 fps on the knee of the curve, and with the 0.219" ports I would have needed to increase the regulator setpoint to 2000 psi.... Now I can use 1900 psi and get there.... I adjusted the gap to 3.5 turns out, and shot the following 10-shot string using the 34.2 gr JSB King Heavies, tethered at 1900 psi....
960
959
956
959
959
957
957
960
955
957
ES = 5 fps = 0.5 %
958 fps average
69.7 FPE average
This achieves my goal with these pellets.... I don't have an efficiency yet, that will have to wait until I install the bottle.... I have not yet decided if I will use my valve, or the Cothran, for the regulated .25 cal, either will work perfectly.... The edge for the Cothran valve over mine is now just 10-20 fps at 1900 psi.... depending on how I adjust the SSG gap.... To adjust the velocity on the Cothran valve, you have to change the pressure, as for best efficiency you need to operate it just above the cliff.... It would make sense to use whichever proved to be the most efficient at the velocity I end up shooting.... That has yet to be determined....
Bob
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Splendid as usual! Would love a video of those dogs barking.
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is that mean that to get to close to zero gap, you could use a weaker spring?? Those number are COLOSSAL...
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Absolutely could use a weaker spring on the SSG.... At 3.5 turns out on the gap (actually about 0.20"), the cocking force is a comfortable 14 lbs.... I am currently using a 0.059" wire 0.48" OD Century spring that is 3" long that is 13 lb/in, and they make a 0.055" at 11 lb/in and a 0.051" wire at 8 lb/in.... either of which will work at 1900 psi.... With the lightest one, the cocking effort should be about 11 lbs. and the gap about 1 turn.... I could also use a much lighter hammer in the regulated one, of course.... and I may try that next, just for giggles.... I'm curious how much an MDS hammer might decrease the gap?....
Bob
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Interesting!!! Since you use your current setup and going with the bottle, i taught you were to regulated it anyway.. The advantage of the back screw is you can at will, change the spring in second.. The bugs are fading away and numbers are great efficiency Wise.. Thanks
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I will likely build one with a regulator and one without.... The .25 cal is looking like it will be the regulated version.... although when I try it with bullets in the 40-65 gr. range at higher pressures, that could change.... The other gun will be either .30 or .357 cal.... The nice thing is that will all the parts interchangeable, I have tons of options.... and of course I could always get another reg. should I decide to regulate both guns....
Bob
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I've been hearing all about these MDS Nylon lightweight hammers, and this gun, with the current hammer spring, needed a large gap on the SSG, so it seemed a good candidate to try one.... I made one of identical dimensions to the steel one I had, but used a 3/4" diam. steel core and the rest is MDS.... I simply knurled a piece of 3/4" steel, drilled it for the hammer spring, and then bored out a piece of MDS of the correct length to be a press fit, and pressed them together.... I then machined the MDS to the correct diameter, cut off the excess steel at the front and turned it to length, and drilled and tapped the 8-32 hole for the cocking pin through both, then machined the angle for the sear in the MDS.... The finished weight was 51 grams, almost exactly 50% of the original steel one, which was 104 gr.... I installed it in the tube with my valve in it, and tethered the gun at 1900 psi, to duplicate the test I did yesterday of the 0.234" ports.... I used the same 34.2 gr. JSB Heavy pellets, so the ONLY change was the hammer.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Light%20Hammer_zpsi9l2yiia.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Light%20Hammer_zpsi9l2yiia.jpg.html)
With zero gap, the velocity was already starting to fall below the maximum, at 963 fps.... This is virtually identical to the velocity I got with the heavy hammer at 3 turns of gap.... The velocity at 1 turn out with the light hammer was almost the same as at 4 turns out with the heavy hammer as well.... Therefore, reducing the hammer weight by 50% required a 3 turn decrease in gap to obtain the same velocity.... The hammer spring I am using has a rate of 13 lb/in, and 3 turns of the gap adjuster, which is 18 TPI, is 0.165".... That means that the light hammer requires just over 2 lbs. more force to cock the gun, and 0.165" more hammer travel, to obtain the same results....
Using Lloyd's hammer spreadsheet, I calculated the hammer velocity at the instant it left the SSG, and from that the hammer energy and momentum.... To do that, I had to include the weight of the SSG guide (22 grams) during acceleration, to get the velocity, and then subtract it to get the energy and momentum of the hammers.... Here are the results that produced identical (963 fps) velocity and FPE in the pellet, which is what matters, of course....
104 gr. Hammer
Velocity 11.54 fps
Energy 0.471 ft.lb.
Momentum 0.082 ft.lb/sec
Lock time 10.1 mSec
Cocking Force 14.4 lbs.
51 gr. Hammer
Velocity 17.83 fps
Energy 0.554 ft.lb.
Momentum 0.062 ft.lb/sec
Lock Time 7.1 mSec
Cocking Force 16.6 lbs.
These results are skewed somewhat by the admittedly heavy SSG assembly in this gun.... as it represents a much higher percentage of the weight of the light hammer than the heavy one.... However, in this particular application, that's what I got.... There is no question that this lightweight hammer will work in this gun, with either valve, at 1900 psi with the 34 gr. JSBs, it would just be a matter of tuning it for the velocity you want.... There is also no question that it requires about a 15% increase in cocking force to get the same performance.... I expected an increase, but it's nice to actually put some numbers to it.... Bear in mind, this is a pretty powerful .25 cal, delivering 70 FPE at only 1900 psi....
Although I did not try it at 2900 psi, the results I could expect were pretty obvious.... I was unable to max. the velocity out with the 34 gr. JSBs at that pressure with the heavy hammer and 0.40" of preload on the spring.... I think I could just get there with 0.60" of preload at zero gap, which would put the cocking force at about 19 lbs.... With the light hammer, I'm pretty sure I couldn't come close to maxing the velocity using an SSG, I would have to go to a preloaded spring.... Using heavier bullets at 2900 psi it would be even harder to flow enough air to max. them out, even with the heavy hammer.... Even the Cothran valve had to have the SSG dialed down to zero gap with the heavy hammer, to get to maximum velocity with my 51 gr. BBTs....
My conclusion is that the MDS hammers certainly have their place, and can do wonderful things at moderate power and pressures.... However, when you are trying to extract maximum FPE, particularly with heavy bullets and at high pressure.... a heavy hammer helps you get the hammer strike required without using a spring that make the gun too hard to cock.... The Cothran Powerhouse valve, with its ability to open with a much lighter hammer strike, can certainly make use of lighter hammers, however.... I have done no efficiency testing with either hammer or valve, so can draw no conclusions regarding that at this time....
Bob
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I realize that you haven't done efficiency testing yet, but would this lightweight hammer be the route to go if one was happy with the current velocity and FPE, and was now looking to maximize their shot count?
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Well done with your build Bob. I am enjoying every step your taking with it. I couldn't be any more happier seeing you ring this platform out.
I know you have always been the disco fan or "custom build" but being your first Mrod build with the vast history of what has been done is a great feeling seeing what your finally doing with it and providing super data to support it.
I actually can't wait to see what happens when you throw that 30 cal barrel on it.
Too be honest, I haven't seen any of your magic on it yet as a very few of us have done what you already have done BUT, I know you gonna push and twist the screw driver in soon and we are gonna be in amazement.....
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Stay tuned.... I frankly have NO idea.... and it very likely depends COMPLETELY on the type of tune you have.... Scott (Motorhead) has spectacular success with low-medium FPE tunes using a light hammer in regulated PCPs, so who am I to argue with success.... The results he is getting may or may not apply to my BRods, with either valve.... I hope to find out if they apply to a regulated PCP shooting at 70 FPE on 1900 psi....
Tim, there is only so much power to be had with a given barrel length and pressure, you know that.... If I was able to break new ground there, we would have to be looking at some new theories.... Still, not too many have reached over 70 FPE with a 34 gr. pellet on just 1900 psi in .25 cal.... I seem to recall a chart you posted just a short time ago that claimed 48 FPE at 1900 psi was about the maximum?.... http://www.gatewaytoairguns.org/GTA/index.php?topic=116706.20 (http://www.gatewaytoairguns.org/GTA/index.php?topic=116706.20) .... I realize that was with 0.187" ports, and I'm at 0.234".... but seems to me that is an improvement, no?.... Using your numbers, with a 0.234" port, you would have predicted about 60 FPE at 1900 psi, if I extrapolated your spreadsheet correctly?....
Bob
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Yup, pretty much true and proved the 60 fpe tune at 1900psi using 43 eujins with the stock barrel using .196" porting.
I definitely see an improvement with your system. That's what I am point out... I think you nailed the plenum size down and the power plant.
Great work and can't wait to see more.
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Bob ...
Can't but wonder in an M-rod that the MDS hammer cocks a LOT easier & smoother too !
By chance did you side flute the MDS hammer to vent it ?
Having an SSG plugging the rear of Vel adjuster that in stock form doubles as a suction vent for hammer bore.
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The calculations you and Lloyd make boggle the mind.
Lock time 10.1 mSec
Steve
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Scott, you might have missed in Reply #66, I vented the rear cap and was able to back the SSG wayyyyyyyyyyy out once I eliminated the vacuum, and the ES went way down as well.... in fact the ES on the last 10 shot string I shot was 5 fps (0.5%).... I don't notice any difference in the smoothness of cocking, but then I'm comparing it to my own cylindrical steel hammer, which I took great care in fitting and polishing....
Bob
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Scott, you might have missed in Reply #66, I vented the rear cap and was able to back the SSG wayyyyyyyyyyy out once I eliminated the vacuum, and the ES went way down as well.... in fact the ES on the last 10 shot string I shot was 5 fps (0.5%).... I don't notice any difference in the smoothness of cocking, but then I'm comparing it to my own cylindrical steel hammer, which I took great care in fitting and polishing....
Bob
Missed that ... my bad :-X
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WOW !! I have been away one day and what a developpement here.. The try was WORTH IT foe sure.. The MAD SCIENTIST is shaking the ole community with some INEXPECTED RESULTS... ;D
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Today I hooked the gun up to a regulated 500 cc tank so that I could take pressure readings on that tank as I shot some short strings to check the efficiency.... I started with the tube with my valve in it, with the MDS hammer.... I adjusted the SSG to zero gap, shot one 8-shot magazine using the 34.2 gr. JSB Heavies, and recorded the average velocity and the pressure drop.... I then turned the SSG gap adjuster out one turn, repeated, and then did the same thing at 2 turns of gap.... I then changed to the 25.4 gr. Kings, shot another magazine with those, and continued, using the lighter pellets, for 2 more turns.... I then replaced the MDS hammer with the steel one, and starting from 4 turns out (where the starting velocity was the same, 945 fps with the 34 gr.), kept going, repeating the above with the steel hammer.... Then I calculated the FPE/CI based on each pressure drop and the total FPE of each string.... and plotted all the data as below....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Efficiency_zpsfjxvpogp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Efficiency_zpsfjxvpogp.jpg.html)
The efficiency is very similar with the steel and MDS hammers.... The gauge I was using to monitor the 500 cc tank had 100 psi increments, so all pressure reading are only within about 10 psi at best, but I feel that the trends above are valid, even if the exact values are not perfect because of the 8 shot strings, which resulted in pressure drops from 120 to 240 psi over the 8 shots.... More accurate numbers would require longer strings..... I also averaged the FPE/CI values at the end of the 34 gr. string and the beginning of the 25 gr. string, because they were pretty close (the heavy pellets were a bit better).... The important numbers, of course, are what the efficiency is at the highest velocities tested (945 fps with the 34 gr. JSBs).... 8 shots used 240 psi with the MDS hammer and 230 psi with the steel hammer, so you can call it a wash (that's as close as I can read the gauge).... That works out to 1.08 - 1.12 FPE/CI at 68 FPE.... and that means I can get about 38 shots per tank from 3000 psi down to the 1850 psi setpoint I was using....
I then swapped tubes, fitting the one with the Cothran valve and the steel hammer.... I had to back the SSG wayyyyyyyyy out to find the cliff, because the last time I used that valve, I was getting a vacuum behind the hammer, which I have since cured.... With the steel hammer, the cliff occurred at just over 8 turns of gap on the SSG, and with the MDS hammer at just over 6 turns.... I followed the same procedure as above, but only using the 34 gr. pellets, with the following results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Efficiency%20Cothran_zpstpnwm13y.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Efficiency%20Cothran_zpstpnwm13y.jpg.html)
I did not record the pressure drop, or calculate the efficiency, after the velocity fell off the cliff, as there was no point, you would never operate the gun there.... I did find that the difference between the valve opening properly and intermittently (fast and slow shots mixed) was only one flat (1/6 turn) with the MDS hammer, and then 1 more flat put the velocity in the basement.... With the steel hammer, just 1 flat went from full power over the cliff.... You can see that as you approach the cliff from the high-velocity end, the efficiency rapidly increases, particularly over the last turn.... A couple of turns too much on the SG, and the efficiency is a dreadful 0.45 FPE/CI, with the gun using about 80 psi per shot.... The best efficiency occurs just above the cliff.... For 8 shots, the best I could do was 290 psi drop with the MDS hammer and 310 psi with the steel hammer.... Again, those are close enough that there may not be any real advantage to either hammer.... It works out to 0.88-0.94 FPE/CI, which is significantly less than I got with my modded valve.... That works out to 30-31 shots per tank, compared to 38 with my valve.... Note, however, part of that will very likely be the fact that the velocity with the Cothran valve was greater.... 970 fps (72 FPE) compared to 945 fps (68 FPE) for my valve.... If they were tuned to the same velocity, the difference in efficiency may well disappear.... However, that would require running the Cothran valve at a lower pressure than my valve.... likely around 1700 psi instead of 1850, to drop it down to 68 FPE.... That would increase the headroom (pressure difference between fill pressure and setpoint) from 1150 psi to 1300, which in itself would raise the shot count to 34-35 shots per fill.... If there was any increase in efficiency, it wouldn't take much to get back to the 38 shots from my valve.... In all fairness, I would have to say that the efficiency of the two valves is VERY similar.... so much so that a tiny tweak one way or the other could make either valve come out on top....
There is another variable that will likely effect the ultimate FPE/CI numbers.... For all versions except my valve with the MDS hammer, there was a lot of gap in the SSG.... A better solution would be to fit a weaker hammer spring to reduce the gap.... Small gaps generally make for narrower ES values.... I would use the MDS hammer with the Cothran valve, in addition to a lighter spring.... the valve takes that little to open it.... One other thing that could be tried with the Cothran valve would be to artificially limit the lift of the valve by using a bumper on the back of the valve, and an adjustable, recessed hammer face, like Lloyd was experimenting with.... It seems to me that the Cothran valve, as is, simply releases too much air to be efficient in .25 cal. with pellets.... To get the velocity low enough you have to drop the setpoint pressure down a long ways.... I have a gut feeling that using a higher pressure, say 2000 psi instead of 1700, and then limiting how far the valve can open with a stop, may increase the FPE/CI.... I hope Lloyd continues his experiments with that at some point.... Using my valve, I think bumping the pressure up a bit, back to 1900 psi, or maybe even 2000.... and then operating the valve further down on the knee.... will improve the efficiency of that as well.... and may well buy me a few shots below the setpoint, giving me a similar shot count to what I have now, at my 70 FPE goal....
Bob
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Wow, that is surprising to me. I expected the lightweight hammer to be more efficient under the circumstances. Thanks for taking the time to run the tests and post the data.
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The results don't surprise me, particularly at the 70 FPE level with 34 gr. pellets in .25 cal. in a 23.8" barrel.... Lloyd's spreadsheet tells me that the valve is open for about 10.5" of pellet travel with my valve (at 945 fps), and about 12.0" with the Cothran valve (at 970 fps).... The valve dwell is over 2 mSec. for both.... It has been my experience that in this power range (valve open for about half the barrel length), the long dwell governs the efficiency more than nearly any other factor.... You already have so much lift, that the flow is being "clipped" because the valve throat limits the area.... To get into the range where subtle changes make a big difference in efficiency, you have to get down to about half that much dwell, in the 1 mSec range, where the valve is closing before the pellet is only 20-25% of the way down the barrel, or less....
If I saw any trend at all, it would be that the MDS hammer seemed to have an edge in efficiency at the lower power levels, where the dwell is much less, and it has a chance to make a difference.... If anything, I think at the top end, with my valve, the steel hammer had an edge.... With the Cothran valve, there is no point in using a heavy hammer, you can max. out the velocity with a light hammer and light spring.... so why not use them....
Bob
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With the Cothran valve, there is no point in using a heavy hammer, you can max. out the velocity with a light hammer and light spring.... so why not use them....
Bob
Yup ... having lower cyclic vibration ( lower mass in motion ) and reduced Lock Time ( Trigger pull to pellet exiting ) Smoother cocking with less wear & tear along with MDS being self lubricating ( No oil to attract and hold debris ) whats NOT to like ;D
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Well Bob those numbers are very interesting especially with the Cothran valve and the MDS hammer and tell me my build may work out quite well with the 26 gram MDS hammer with an aluminum core from Motorhead and a TSS from Travis with the Cothran valve and the reg set at 2000 to 2200 psi with a 500cc bottle.
I am still looking at using a CF bottle to up the pressure in it to 4500 with a 3K burst disc to protect the gun from reg bleed out. I know if I don't go to the 1/4" port I may have to use the 2200 psi on the reg to get close to the 930/950 fps range and is the driving reason for the 4500 bottle to compensate for the higher reg set point. Even if I can only get to 900 fps with the 3/16" ports and 2200 psi I will be happy for that. I am after good power with a high shot count being slightly more important then power.
I mainly am after a accurate gun for 100 yard bench rest shooting at our FT clubs sight in range that has spinners and reactive targets from 10 to 100 yards every 5 yards. We have some friendly long range competitions after the matches and soon will be holding long range silhouette matches as well. That and I would like to be able to show one member that you don't need a 2500 dollar RAW HM1000X to be able to shoot accurately out to 100 yards.
Mike
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I'm testing Cothran valve with stop buffer and adjustable hammer and it looks like it is not possible to adjust the velocity by limiting the hammer throw. The valve simply is either on or off. Too little throw and you're off the cliff like with hammer spring adjustments and with too much throw you're wasting air. The optimum setting for effiency seems to be less than a quarter turn more on the hammer throw from the point being off the cliff.
For example on my bottlepup, regulated at 1700psi with .25 24gr JSB's the fps stay at 920-935 range no matter how much hammer throw. Unless too little throw and then it drops down to 435fps.
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Amazing stuff and my hats off to your sir. That was alot of work.
The only thing in my head keeps asking, why doesn't the Cothran valve close faster and how do you get it to close faster? In both cases heavy hammer vs light weight hammer, the efficiency was nearly the same.
Too me,
That indicates that the dwell will not be affected by an absorbing material like I messed around with (elastic collision/in-elastic collision) controlled lift. I bet, that your only gonna see (big swings) if the reg pressure is changed ( higher or lower) until the sweet spot is found for valve closing (dwell).
Really interesting about the balanced valve. I am also curious to know if the balanced valve can be adjusted (internally) to operate at different pressures to reduce dwell. There's gotta be a "mechanism" in the valve design to do this ( I would think?).
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Jari, the setup Lloyd was using did not adjust the hammer throw per se.... It used a recessed, adjustable striker, and the face of the hammer hit an energy absorbing bumper on the back of the valve.... The way he used it, the hammer ALWAYS hit the valve and stopped.... The valve stem protruded past the face of the bumper material.... The amount of recess for the striker governed how far the stem of the Cothran valve was pushed by the hammer before it stopped.... By increasing the recess in the hammer face, the valve opened less.... and vice versa.... If the striker was set flush with the hammer face, whatever the distance the stem was above the bumper, was the valve lift.... The hammer strike was always enough to operate the valve above the cliff.... The only thing that varied was how far the valve stem got pushed on firing.... It provided control over the power, allowing another way of tuning the Cothran valve without having to change the pressure to change the velocity....
Tim, I haven't been inside the Cothran valve.... Like Lloyd, I view it as a "black box".... a Proprietary design that works very well for what it was designed to do.... flow a LOT of air with a light hammer strike.... The only way to tune the velocity, other than what I describe above, is to vary the operating pressure.... More pressure, more velocity.... This results in a constantly decreasing shot string in an unregulated PCP, with the first shot (at the highest pressure) the fastest.... This meets its original intended goal of a high powered hunting valve extremely well.... with way over 200 FPE available in a Disco or MRod at 3000 psi, with a standard hammer and likely a lighter than stock spring.... The amount of power it can generate with light cocking force is quite amazing....
The Cothran valve has a "cycle time" which you can consider the dwell.... It is basically either ON or NOT.... That is why hammer weight, or spring preload, has almost no effect on the power, because it doesn't change the dwell much.... I have no idea if that time is relatively fixed, or if it changes with air pressure.... I know from previous testing that the valve cycling DOES vary with backpressure, it works differently with different pellet weights.... If you tune the gun just above the cliff, and change to a lighter bullet, it "falls off the cliff" and shoots a low velocity shot.... Likewise, if you shoot without a bullet in the barrel, the valve closes very quickly, with a much reduced report, ie it doesn't cycle as intended.... If you want to really understand the Powerhouse valve better, I suggest you study my thread on the tests I did in my Disco Double with one.... http://www.gatewaytoairguns.org/GTA/index.php?topic=117089. (http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.)
Don spent a lot of time getting the internals to work the way he wanted.... I have no idea what changing things around in there would do to the way it operates.... I'm betting you could custom taylor it to work differently.... Perhaps you should get one and tear into it to satisfy your curiousity....
Bob
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I just posted about casting the new 68 gr. BBTs using the RG series moulds in the Big Bore Gate.... http://www.gatewaytoairguns.org/GTA/index.php?topic=120719.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=120719.0)
I'm looking forward to testing these in my BRods once I get the .30 cal TJ's barrel installed....
Bob
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Today I moved back the port in the .30 cal barrel that I had to line up with the port in the MRod receiver.... I was able to get everything to line up without having to cut another O-ring groove, shorten the barrel and machine a new chamber, so that saved me a LOT of time.... The new barrel port is 0.22" wide by 0.28" long, so it is the same area as the 1/4" transfer port.... and the new spot face around the port is 3/8" to match the receiver, valve, and the OD of the transfer port.... The barrel was already machined for a Hatsan Air Stripper, so with just the change in port location it was ready to fit with a Carbon Fibre sleeve to stiffen it.... The barrel is a TJ's with a 1/2" OD and I had some high modulus CF tubing of that ID that was 16mm OD, the same as the .25 cal LW barrel I used, which I had already machined the receivers to fit.... By insetting the CF tube into the receiver, there is no weak area at the front of the receiver for the barrel to bend, and the high-modulus CF the tube is made of is 50% stiffer than normal CF, which puts it at least as stiff as a steel barrel of the same diameter.... Instead of being able to flex the barrel with your hands, once sleeved, it's like a rock....
I sanded the barrel OD and the ID of the tube with 220 grit to give a bit of "tooth" for the adhesive.... I used Loctite 638 (green) which is high-strength, high-viscosity, intended as a retaining compound for slip-fitted parts with a gap of 0.010" or less.... It has a shear strength of 4500 psi once cured, stronger than most epoxies, has a working time of 4 minutes (or less) and a curing time of 24 hours.... Once cured, I will be giving it a post cure in my wife's oven at 175*F for 3 hours to assure full strength.... You MUST assure that the parts slide together nice and easy, if they stick and you have to force them, you may run out of time, because the tighter the fit, the quicker 638 sets to the point you can't move it.... I used two nuts on the threaded muzzle portion, and an O-ring, as a stop for the sleeve, to insure proper placement.... but a few wraps of masking tape will also work just fine.... Make sure you have the CF tube exactly the length you want, and know where you want to position it, before you apply any glue.... Make sure you plug the ends of the barrel and any ports, with wadded up paper towel, etc., to keep the glue out.... Here is what it looks like with the CF tube glued in place....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20barrel_zpswyvqvkdk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20barrel_zpswyvqvkdk.jpg.html)
The portion of CF tube in the receiver is about the same length as the steel part where the port is.... I had to drill out the cone of the Hatsan Stripper to 11/32" to have ample clearance for the .30 cal bullets.... This one started out drilled for a .177 cal.... The other job I did today was to change the cocking and lockup pin in the bolt to 10-32 for safety with the extra loads from the .30 cal.... At the same pressure, the force pushing the bolt back is 44% greater than on a .25 cal, and going up from 8-32 to 10-32 increases the shear area by 45%.... In the .30 cal, at 3000 psi, there is 212 lbs. force on the bolt, and although the stock 8-32 should be able to handle that, if you ever fired the gun without having the bolt handle down, that force would accelerate the bolt backwards, with only that 8-32 bolt to stop it before it hits your face.... We have never heard of Crosman having a problem, but the MRod only goes to .25 cal from the factory.... Using a 10-32 gives me the same safety margin with my .30 cal.... Here is a photo of the receiver showing the new pin and the wider slots for it....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20Receiver_zpstcib1i3w.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20Receiver_zpstcib1i3w.jpg.html)
The MRod bolt is case hardened, so the first thing I had to do was heat it red hot around the threaded hole for the pin, and from there forward.... By letting it cool slowly, it anneals the steel, making it much easier to machine.... although there is still a bit of a tough skin.... I carefully lined up the 8-32 hole with my lathe chuck, using a long screw in the chuck, and clamped down the bolt.... I then removed the screw from the chuck, and drilled the hole out and tapped it 10-32.... One tap I had was a bit older, and I thought I might break it, as the metal was still hard to thread.... but my other tap, a nice new one, cut the threads no problem.... I then used a 1/2" long 10-32 SHCS, and loctited on a hex nut, tightened hard against the head of the screw.... I turned the nut, and the head of the screw down to 1/4" OD, and shortened the head about 0.025" so that it was just below flush in the receiver when installed.... I had to mill out the cocking slot in the receiver wider as well, along with the cross-slot on the left side (I will only be installing the handle on the right) so that the new, larger locking pin would fit....
The last thing I did today was to grind off the probe and the nose of the bolt, leaving a 1/4" stub about 3/4" long.... I will make a new .30 cal nose with probe that will be slid over the stub and loctited in place to complete the conversion of the receiver to .30 cal....
Bob
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Where do you get those sleeve??? I saw that you have used it in another build.. Would they work on the crosman barel??? Your rifle is comming along nicely and the end product will be one of a kind...
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There are a few companies that sell CF tubing online....
http://www.clearwatercomposites.com/Products/carbon-fiber-tubes/round (http://www.clearwatercomposites.com/Products/carbon-fiber-tubes/round)
https://dragonplate.com/ecart/categories.asp?cID=263 (https://dragonplate.com/ecart/categories.asp?cID=263)
https://www.rockwestcomposites.com/ (https://www.rockwestcomposites.com/)
Lots of listings on eBay, most out of China (not a problem, I have bought a few, but usually Metric), and a few "surplus" CF tubes from US suppliers.... lots of sources online.... You would need a 7/16" ID tube for many of the common Crosman barrels.... I haven't (yet) dealt with dragonplate, but I like the variety of wall thickness and material they have listed....
Bob
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And would you suggest the addition for a crosman barel... I always pay close attention to my 2240 while hunting with it but noticed how easy it is to move around.... The addition is it enouf to STABILIZE with a steel breach??
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And would you suggest the addition for a crosman barel... I always pay close attention to my 2240 while hunting with it but noticed how easy it is to move around.... The addition is it enouf to STABILIZE with a steel breach??
Not sure how much it will help without the CF shroud being inside the breech like Bob does his, The 2240 steel breech would not allow for the shroud to be fitted inside it since its only slightly bigger than the barrel itself. If you had a aftermarket breech that could have the hole drilled out to allow 2 inches or so of the shroud to fit tight inside the breech it would certainly help stiffen it up. Otherwise the barrel is still the only thing inside the breech to provide any real support for flexing at the breech. It would stiffen the barrel outside the breech but could allow the barrel to bend at the breech if hit hard enough on a branch or tree trunk.
Mike
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Alain, the barrel on a 2240 pistol is so short I don't know if I would bother.... Also, there is no room for a CF sleeve between the barrel and the main tube anyways, the clearance is about 1/32".... As Mike says, for best results the CF sleeve needs to be set into the receiver at least 2 diameters, and 3 would be better.... Mine is about 2-1/4 diameters, but picks up extra stability because the barrel goes that far again into the receiver.... Believe me when I say the barrel on this gun doesn't flex relative to the receiver.... 8)
I finished up the .30 cal Bolt conversion today by increasing the diameter of the forward section.... Now you can clearly see the larger cocking / locking lug....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20Bolt_zpsmdxtudva.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20Bolt_zpsmdxtudva.jpg.html)
I ground off the probe, leaving a straight 1/4" diameter shank 3/4" long.... and then made a sleeve to slide over the 1/4" diameter shank from a piece of 5/16" drill rod.... I turned the front part down to form a probe that is 7/64" in diameter, which just fits inside the base of the JSB 45 gr. and 50 gr. pellets.... The flow area remaining around the probe is the equivalent of a 0.280" port, and the ports in the barrel and Cothran valve are only 1/4", so it should not restrict the flow.... I turned down (filed and sanded, actually, in the lathe) the OD so that it would just slide into the chamber of my .30 cal barrel, checked the alignment, and glued it onto the stub of the bolt with Loctite 638 (green) and allowed it to set....
The shoulder on the bolt nose is located so that the outside edge of it is flush with the back of the barrel port.... and the probe will just push the skirt of the JSB pellets past the front of the barrel port.... When you are making a longer, thinner probe, you are limited in the overall length by how far it will withdraw to clear the back of the magazine.... With the hammer and cocking pin in place, I temporarily install the receiver, with the bolt in place, and pull it back as far as the hammer will allow it to go.... and then mark and cut the probe off flush with the back of the magazine notch.... That will still be a bit long, once you install the trigger, the hammer when cocked will sit slightly forward of that point, and you may have to shorten it a bit more.... The problem is, that if you do, it may not push pellets past the longer barrel port, so you may be stuck with having to hold the bolt back to remove the magazine.... On my .25 cal, I am just able to remove the mag. with the gun cocked, I won't know on this one until the final assembly.... Worst case, I don't mind holding the bolt back to remove the mag. if that is the only way to get the pellet past the barrel port.... Like with many conversions, there is often just enough (or not quite enough) room for things like this....
Bob
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Thanks for the precision about the barel and will consider trying if i change my breach for a magazine fed.. Your project is riding really smooth..
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Nice looking work Bob, don't you just love to turn those small probes on a lathe that doesn't spin fast enough.
I'm limited to around 1800rpm on my lathe and anything smaller than 3mm is files and sandpaper.
Is there any room to extend the cocking slot if the mag won't fit?
Marko
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Oh, I was able to turn the probe no problem, it was the OD of the .30 cal section that had so little to remove it wasn't worth trying to get it to run true in my 3-jaw.... easier to just file and sand it to fit the chamber.... The length of the cocking slot is not the problem, the position where the cocking lug on the hammer stops is already set, and the front edge of that governs how far back the bolt can withdraw.... I checked it today before assembly, and I only had to remove another 0.020" to make it operational.... I have to hold the bolt back to remove the magazine, but next time I pull it apart I will see where the pellets load relative to the barrel port, I only need to remove another 0.020" and I won't have to hold the bolt back against the hammer spring to swap the mag....
I assembled the .30 cal version today, using the tube with the Cothran valve and the MDS hammer, and did some test shots tethered at 1900 psi and also at 2900 psi.... After about 20 shots at 2900 I started to get some blowby, and within 3 shots, it was severe, with a 200 fps velocity drop.... I pulled the gun apart to find this....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Collapsed%20Transfer%20Port_zpsdpiy5f5h.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Collapsed%20Transfer%20Port_zpsdpiy5f5h.jpg.html)
Yep, that's whats left of the Teflon Transfer Port.... Looking at the damage, I think the bottom edge which was thinned out to clear the O-ring in the Cothran valve failed, which let HPA out between the valve and the OD of the port, which then collapsed the port.... Interesting failure, anyway, and the first time I have had a Teflon TP do anything strange.... If there was no O-ring in the Cothran valve, and the TP tube was full thickness to the bottom, I think it would have been fine, as I have used them at much higher FPE and pressure levels.... Anyway, I'll have to come up with a solution, maybe just use PEEK?....
I was quite pleased with the numbers I achieved.... I tested both the 45 gr. and 50 gr. JSB pellets at 1900 psi, and then tested some NOE 67 gr. BBTs and also some Accurate 71 gr. BBTs at both pressures.... Here are the results, with the SSG gap adjusted so that the valve is operating just above the cliff.... NOTE - I EDITED THE TABLE BELOW AFTER MAKING A BRASS TRANSFER PORT - I GUESS THE TEFLON ONE WAS FAILING, BECAUSE I GAINED 50 FPS ON THE 2900 PSI SHOTS....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran2_zpszgoxrpzu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran2_zpszgoxrpzu.jpg.html)
These represent some pretty impressive power at those pressures.... I now have to make the same tests on the other tube assembly, with the steel hammer and my modded valve.... I got my new NOE .253 cal 51 gr. BBT mould today, so once I get some cast up I will be able to see what these guns will do with those at 2900 psi.... I also need to try the 41 gr. BBTs as well.... so lots of testing ahead yet....
Bob
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I had same failure 3 times today with Cothran valve blowing out delrin so I made and alloy Tport and the awesomeness of his valve just shined like gold bullion. I used and over travel limiter and MDS hammer and all I can say is WOW!!!!!
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Lol .... Not really laughing, just acknowledgment of the why I have been painstakingly fitting PEEK transfer tubes for a few years now in those applications where BIG and THIN WALL have been used together.
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I see that you made a brass Transfer port to replace the Teflon one that imploded from the HPA blast but was just wondering if you could have just done away with the o ring in the Cothran valve and made the Teflon the same thickness for its full length instead of thinning it for the o ring at the valve end. I don't really see the need for the o ring with a Teflon TR or any other material that is used as a crush type of seal for the TP.
That failure really shows the power of HPA in a confined area and how it will find a path of least resistance to escape to the atmosphere.
Mike
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The Cothran valve has a 3/8" ID hole to hold the transfer port, but right at the bottom of that hole, it has a half-depth O-ring groove to retain a # 011 O-ring, that is nominally 5/16" ID x 7/16" OD.... This requires that the bottom 1/16" of the transfer port (it is intended that it be made from brass) is turned down to 5/16" OD.... I did that with my Teflon port, which for that bottom 1/16" left the wall thickness only 1/32", and it looks like that is what failed.... I thought about doing as you suggested, and leaving the Teflon 3/8" OD right to the bottom, but then the bottom 1/16" (maybe 0.070") would be unsupported because that area in the valve port recess has been removed to form the groove in the valve for the O-ring.... I was concerned that the TP would fail in that area, blowing outwards, or at the very least expand, locking the TP into the groove in the valve.... After examining the alternatives, I decided to use brass, and seal it at the top, against the barrel, with an 8mm x 10mm x 1mm Metric O-ring located in a shoulder in the top of the Transfer Port.... I made the brass transfer port with a 0.060" long shoulder (5/16" diam.) at the bottom, and a few thou long at the top, and then machined the length down until I could just push the receiver down against the main tube, by compressing the O-ring in the valve.... Being brass, the length is, of course, critical.... I then machined a shoulder 0.035" smaller in OD, and 0.035" deep, into the top end of the transfer port.... This puts the 1mm O-ring into significant compression.... I only tried a few shots, but it sealed perfectly, and I picked up 50 fps.... That makes me quite certain that the Teflon port started to fail almost as soon as I began testing at 2900 psi, which caused the velocity loss.... It is possible that it may have even affected the 1900 psi tests, that will be determined another day....
In the meantime, I am pretty stoked to break 150 FPE at 2900 psi.... :o 8) ;D
Bob
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Very nice power from your combination, Bob. The thin wall at the input end of the soft T-port can definitely cause problems once the air gets behind it. I am glad you got the brass port sorted out.
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I couldn't get what I would call a commercial seal on Dons Valve with that oring gland at the bottom so I bored it out and made a compression oring seal like on the Flex. I think it's the only part of the valve design that needs to be re done. I put his valve with a oring over travel buffer in and I'm having awesome results. I know have tons of adjustments with pressure and hammer striker and spring tension. Super Happy!!!!
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I ran all the tests again, with more bullet weights, and determined the position of the cliff.... As expected, it is a bit different with pellets than with bullets.... The lighter pellets need 1/2 turn less SSG Gap (ie slightly more hammer energy) to stay above the cliff.... Here are those results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg.html)
It only takes 1 flat (1/6 turn) on the SSG to go from operating properly to being intermittent, and another flat to see the velocity in the basement.... For the velocity tests with the different bullets I adjusted the SSG so that it was solidly on the plateau.... I added the 62 gr. NOE HollowPoints to the testing today, and also I had some .308 cal 80 gr. BBTs from Accurate that I sized down in 2 step) so that I could try them in this barrel.... All the bullets shot today were sized to 0.300".... Here is the expanded table of results at 1900 and 2900 psi with all bullet weights tested....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran%20Velocities_zpsn0d4v30b.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran%20Velocities_zpsn0d4v30b.jpg.html)
Note that the Cothran valve pushes bullets faster at 2900 psi than pellets at 1900.... I didn't do any efficiency testing yet, I'm going to test my modded valve first, putting it through the same tests as I did today with the Cothran....
Bob
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That is huge power!! May i ask why the heaviest bullet has a different curve or dramatic change in the turns you have with the SSG??
The fps is so constant troughout the settings that i Wonder if you maximized the efficiency right before the cliff..
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Alain, the black line on the graph above is at 2900 psi, the red and blue are at 1900 psi.... It is the extra pressure that requires a drastic reduction in the SSG gap to increase hammer energy.... The blue and black lines are the same bullet weight, just different pressures....
I started testing my valve today, and got some data at 1900 psi, but when I changed to 2900 the valve started to leak air out the barrel.... I took a bit more data, figuring it would probably be OK, but the leak got worse so I had to degas the gun and pull it apart.... I lapped the seat and poppet and reassembled, and it still leaked.... I put some soapy water in the exhaust port, and it looked like it was bubbling from the right side, where I had plugged the velocity adjuster hole with epoxy when I inserted the larger, longer seat into the valve when I modded it.... I stripped it apart again, cleaned it thoroughly, and put on some penetrating Loctite, the thin green kind that wicks into threads, hoping it would wick into the cracks and seal them.... I will try it out tomorrow, if it still leaks, I may need to make another valve....
I made an interesting discovery down at my bullet trap this afternoon.... It has several sacrificial layers of particle board, backed by a steel plate, and with all the shooting, it had carved a hole through the layers of wood, down to the steel.... I found these two flattened BBT's laying on the floor, just in front of the trap....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BBT%20at%20150%20FPE_zpsbkmjvqpz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BBT%20at%20150%20FPE_zpsbkmjvqpz.jpg.html)
Pretty KEWL, what 150 FPE can do.... *grin*....
Bob
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The picture reminds me of the fly joke. " what's the last thing to go through a flys mind as he hits a windshield ? ............... his @@@. " . Too bad about the valve leak Bob. I'm sure you'll have it sorted out soon enough .
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The Cothran valve has a 3/8" ID hole to hold the transfer port, but right at the bottom of that hole, it has a half-depth O-ring groove to retain a # 011 O-ring, that is nominally 5/16" ID x 7/16" OD.... This requires that the bottom 1/16" of the transfer port (it is intended that it be made from brass) is turned down to 5/16" OD.... I did that with my Teflon port, which for that bottom 1/16" left the wall thickness only 1/32", and it looks like that is what failed.... I thought about doing as you suggested, and leaving the Teflon 3/8" OD right to the bottom, but then the bottom 1/16" (maybe 0.070") would be unsupported because that area in the valve port recess has been removed to form the groove in the valve for the O-ring.... I was concerned that the TP would fail in that area, blowing outwards, or at the very least expand, locking the TP into the groove in the valve.... After examining the alternatives, I decided to use brass, and seal it at the top, against the barrel, with an 8mm x 10mm x 1mm Metric O-ring located in a shoulder in the top of the Transfer Port.... I made the brass transfer port with a 0.060" long shoulder (5/16" diam.) at the bottom, and a few thou long at the top, and then machined the length down until I could just push the receiver down against the main tube, by compressing the O-ring in the valve.... Being brass, the length is, of course, critical.... I then machined a shoulder 0.035" smaller in OD, and 0.035" deep, into the top end of the transfer port.... This puts the 1mm O-ring into significant compression.... I only tried a few shots, but it sealed perfectly, and I picked up 50 fps.... That makes me quite certain that the Teflon port started to fail almost as soon as I began testing at 2900 psi, which caused the velocity loss.... It is possible that it may have even affected the 1900 psi tests, that will be determined another day....
In the meantime, I am pretty stoked to break 150 FPE at 2900 psi.... :o 8) ;D
Bob
Bob
I wondered about the Teflon TP sealing without the o ring there and no relief cut into the Teflon TP as well. That as you said it may likely fail like the one you had did only in the opposite direction with the pressure expanding it into the o ring groove in the valve ports seat. I am glad you got the brass TP to seal and used captured o rings at each end that hopefully will hold up to the volume of air that the valve is capable of flowing thru it.
A gain of 50 fps is quite a bit and indeed shows the Teflon TP was leaking from the start and progressively got worse until it failed. It has me wondering if I need to use the steel TP that Don supplied me with the valve even though I am having issue getting the TP to seat properly in the valves port. It has the o ring that yours has for the reducing bushing and then the bushing has a groove cut in the bottom of it the same as the valve to capture a o ring between it and the lower end of the TP and is where I am having trouble keeping the o ring in place without it moving under the thin lip on the TP that should capture it.
The testing is going very good for sure and making 150 fpe is some real power in the 30 cal so just hope both guns group as well as they make power. I am very confident that they will group excellent also.
Mike
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The leak around the insert I made persisted.... so it was time to remake my valve.... I talked to Travis at W.A.R. and he suggested I bore the valve out 1/2" straight through and make a new insert and seal it with O-rings.... Here is what I came up with....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Valve%20insert_zpsdma6cx4q.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Valve%20insert_zpsdma6cx4q.jpg.html)
This is a pretty radical repair job, but it gave me the opportunity to do some neat things.... I made the insert a bit longer, to make room for the front O-ring ahead of the port, and enlarged the exhaust port to 1/4" at a 20* angle (same as the 7/32" port was before).... I drilled the throat out to 9/32" to handle the flow of the larger port, and made a PEEK poppet to handle the loads of the larger seat.... This makes the exhaust port basically the same size as the Cothran valve, and as the transfer and barrel ports....
The details of this mod are pretty much explained in the photo above.... The insert is 1/2" OD, sealed with two # 012, 90D O-rings.... There is another hole in the valve for a 10-32 setscrew, in the same plane as the three valve mounting screws, and a dimple in the top of the insert for that to tighten into.... That holds the insert securely in the valve while you machine the port and the three holes for the valve mounting screws.... They are blind holes in the insert, tapped 1/8" deep, using the threads in the valve as a guide, which requires slightly longer valve screws, as the same screws hold the valve and insert in place against the 3000 psi reservoir pressure.... The poppet is made from PEEK, with the stem from 1/8" drill rod, threaded 5-40 into the PEEK.... The stem is 0.070" longer than stock (for my shortened valve).... in a stock length valve it would be even longer....
I assembled the valve and installed it into the tube and it held pressure beautifully.... I then set about testing the .30 cal setup with this new valve.... I had hoped that the PEEK would make up for the larger throat, and not require more hammer strike, but alas that was not the case.... I had to use significant preload at 2900 psi, and a bit of preload at 1900 with bullets.... At 1900 psi with pellets, I had to use preload to max. out the velocity, but the knee of the curve is right about at zero gap on the SSG.... Here is how the gun responds the hammer preload, using the same pressures and pellets as I did for the Cothran valve above.... 6.8 turns out from max. is "zero" gap for the SSG, so at 7 turns and out the SSG is operating, at less than 7 turns there is preload on the valve stem....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20PEEK%20Tethered_zpscxuwkahb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20PEEK%20Tethered_zpscxuwkahb.jpg.html)
When the hammer strike was on the plateau, here are the velocities I achieved with the various pellets and bullets at 1900 and 2900 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20PEEK%20Velocities_zpslvdxpccr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20PEEK%20Velocities_zpslvdxpccr.jpg.html)
Comparing these maximum numbers to the Cothran valve, at 1900 psi there is virtually no difference in fps or FPE.... At 2900 psi, with pellets my valve is almost there with the Cothran, but with bullets I am losing just a bit with the 62-71 gr. bullets and about 10% less FPE with the 80 gr.... I think I may be running out of hammer strike with the heavier bullets, and the difference between the two valves is now insignificant (as you would expect, with equal ports) except for one thing.... My valve is a LOT harder to open, compared to the Cothran.... I'm using a steel hammer that weighs 104 grams, and a lot of preload on the spring, compared to the Cothran, where I'm using an MDS hammer that weighs 51 grams, and lots of gap in the SSG, in fact I could reduce the preload, or fit a lighter spring.... Don's Powerhouse valve sure is EASY to open.... On the other hand, I can tune my valve down onto the knee of the curve, which should make it more efficient.... I think it's time to start trying to work on improving the efficiency of the Cothran valve by making an adjustable lift arrangement so that I can lower the velocity when using the Cothran valve without lowering the pressure....
Bob
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Well look at you go!!! That looks fantastic and now you can change valve seats and ports at will!!!! Pretty nice work there my friend! I did my seat a little bigger but same idea as I wanted more threads in the insert. Now just pop it out anytime you need to adjust throats or T port area. This guy had a 450 Throat and 300 T-port ! Kaboom!!!
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Yeah, with a 1/2" OD insert you have to use longer screws, the stock ones are too short to give it enough support.... Of course with a larger OD insert, the loads are higher, so the longer screws are probably still a good idea anyway.... You can certainly hog everything out this way.... and you have the added benefit of being able to guarantee that the seat is at 90* to the valve stem hole, 'cause you're not working down inside the valve.... I see you didn't bother with a rear O-ring, no problem with air escaping into the hammer space during a shot?.... That's why I put one there, plenty of room aft of the screws, even in my shortened valve, tons of room in a stocker....
Certainly eliminates the problem of a stock MRod valve not having enough room for a big exhaust port.... Thanks again for the idea, Travis.... much appreciated.... 8)
Bob
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I like your rear oring idea Bob and the other thing we can do is use epoxy to build a smooth ramp up to tport now that it's easy to get to.
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Another trick ( design you can use now ) is that of keeping the poppet head diameter smaller for easier opening by going to a tapered seat like an automotive head valve.
All my personal PCP's with Peek poppet heads have been done this way for a few years now.
Seat / Head on an @ 15* angle having the sealing margin very near the O.D. edge of poppet.
Here is what I use in my M-rods based on a .250 throat valve. Poppet O.D. is @ .300" having sealing margins of .020" just .005" from the O.D. diameter.
* Being the seal between the two is across a flat the peek has not shown but minor extrusion into the throat at @ 2K working pressures ( regulated actions )
(http://i1320.photobucket.com/albums/u532/scott_schneider1/DSCF9900_zps0wyqtzkr.jpg)
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Or go exotic and use two stage poppet with big throat!
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I went back to the tube with the Cothran valve today, looking to experiment with varying the lift at 1900 psi.... First I had to make a hammer with an adjustable striker position.... This is the second MDS Nylon hammer I have made, and this time I decided to make it even lighter, with an aluminum core.... They are pretty simple to make, actually.... I started with a piece of 3/4" aluminum, faced it off and drilled it through with a #3 drill (the tap size for 1/4"-28 threads) and then used a 1/2" end mill to create the spring cavity 3/4" deep.... I then knurled the outside longer than the hammer, but leaving a smooth area I could hold in the lathe chuck.... I bored a piece of MDS to a few thou over 3/4", but about 0.010" smaller than the OD of the knurling, faced both ends square to a length of 1.25", and pressed them together to form this....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/MDS%20Hammer_zpsirubccns.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/MDS%20Hammer_zpsirubccns.jpg.html)
I then turned the OD to finished diameter to slide smoothly in the tube, and holding the stub of aluminum in a collet I drilled and tapped two 8-32 holes, one for the cocking pin and one for a "brake" to prevent the adjusting screw from adjusting itself.... I then faced off the length at the nose, added the taper for the sear, and tapped the nose through to 1/4"-28, ground the cup point off a 1/2" long setscrew, and installed it with the allen key hole on the inside.... I then dropped a 1/8" long piece of 1/8" diam. Delrin in the front hole, against the side of the adjuster, and topped that off with a 1/4" long 8-32 setscrew, tightened against the Delrin, pressing it into the threads of the adjuster.... Now I can adjust the striker from flush 3 turns in either direction, which is greater than the length of the valve stem on the Cothran valve, so I can go from full lift to no lift in (just under) 6 turns.... Here is the finished hammer, which weighs 28.4 grams (exactly 1 oz.)....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Adjustable%20Hammer_zpsgbuurzdm.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Adjustable%20Hammer_zpsgbuurzdm.jpg.html)
I had a small scrap of energy absorbing polymer sheet about 3/32" thick from Lloyd, which he used in his Cothran valve experimenting, and cut a washer from it with a 3/8" hole (for the striker to clear) and the OD a snug fit in the tube, and installed it hard up against the back of the Powerhouse valve as a bumper to stop the hammer and absorb it's energy.... I removed the spring guide from my SSG, so that I could access the lift adjuster from the back with a long 1/8" allen key, and using the same hammer spring as before, reassembled the gun.... I set the preload on the spring to zero (with the striker just touching the valve stem) with the striker set flush with the face of the hammer.... Assuming the hammer hits the bumper, the valve stem will be driven open about 0.108", and at 0.036" travel per turn of the adjuster, that means that 3 turns out (proud of the hammer face), the striker will push the valve fully open, and backed out about 2.5 turns below flush, it won't open the valve at all.... That was the theory, anyways....
I reassembled everything, tethered the gun at 1900 psi, loaded up a mag. with 45 gr. JSBs, and took a shot.... I had no idea if the valve would cycle properly at these settings or not, and smiled as the shot went through the Chrony at 978 fps, exactly the same as the plateau velocity I had before.... I checked the velocity with more spring preload and it stayed the same, as expected, then reduced the preload, no change at 1 turn of gap, a few fps less at 2 turns, but at 3 turns of gap it dropped to 284 fps.... OK, so there is the normal "Cliff" for the Cothran valve.... I set the preload at 1 turn negative (ie 1 turn of gap), and started adjusting the lift by moving the striker in and out.... When I increased the lift (striker extended), the velocity stayed the same, as expected.... Then I started backing it out, below flush, to reduce the lift on the valve, while leaving the valve cycling properly by virtue of having lots of hammer strike.... I was hoping to be able to have much finer control over the velocity, to give me the ability to control the velocity on the Powerhouse valve without having to change the pressure.... Unfortunately, I was disappointed....
As I recessed the striker into the valve, at 1 turn below flush the velocity held steady at 978 fps.... I figured, "OK, this valve doesn't need much lift".... At 2 turns below flush, I got 321 fps.... much like I did when changing the preload a turn, the valve either cycled or it didn't.... At 2.5 turns out, or further, the valve didn't open, exactly as I had hoped, no shot at all occurred.... I tried various combinations with more preload on the spring, to make sure that I had LOTS of hammer strike, and could not get away from that annoying cliff.... If I was just 1/6 turn (one flat on the allen key) more recessed than where the velocity was steady at 978 fps, the velocity was unstable, it could be anything from under 600 to over 800 fps.... As I recessed it more, the velocity range dropped, but it was still not stable, fluctuating 100 fps or more, shot to shot.... If anything, I think the velocity was more stable with the valve lift greater, and reducing the preload.... I'm pretty frustrated at this point.... Travis suggested I try a heavier valve spring, but I don't have anything suitable, unfortunately.... At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....
Bob
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Take the spring out and stretch it and shim it. Theres plenty of room and once you have more spring rate the valve adjustments can be made but not in small amounts but you will be able to get some adjustment and not just have and on off switch. But like you said its all about matching the pressure to the valve not about dwell and lift.
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I "may" have a spring available locally next week.... the diameter will be OK, but the guy didn't know the wire size.... it wasn't listed in the catalogue.... *LOL*....
I may have to wind my own, if I have any suitable wire kicking around.... What is the wire diameter in the one you are using, Travis?.... Sounds like a stiffer spring just makes the slope of the cliff a bit shallower?.... not a rounded curve with a knee, but a steep hill instead of a cliff?.... How stable is the velocity if you tune 50-100 fps below the plateau, like you normally would on a conventional valve to tune on the knee?.... Is the ES low, or does it jump around?.... In other words are we really just spinning our wheels here?....
Bob
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Or go exotic and use two stage poppet with big throat!
Been a while since I've seen that one.... ;)
http://www.network54.com/Forum/519893/thread/1164752966/big+bore+co2+valve (http://www.network54.com/Forum/519893/thread/1164752966/big+bore+co2+valve)
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I "may" have a spring available locally next week.... the diameter will be OK, but the guy didn't know the wire size.... it wasn't listed in the catalogue.... *LOL*....
I may have to wind my own, if I have any suitable wire kicking around.... What is the wire diameter in the one you are using, Travis?.... Sounds like a stiffer spring just makes the slope of the cliff a bit shallower?.... not a rounded curve with a knee, but a steep hill instead of a cliff?.... How stable is the velocity if you tune 50-100 fps below the plateau, like you normally would on a conventional valve to tune on the knee?.... Is the ES low, or does it jump around?.... In other words are we really just spinning our wheels here?....
Bob
It will lower the ES and give you a steep wall to climb but every bit helps. Its still a balancing act with pressure.
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Or go exotic and use two stage poppet with big throat!
Been a while since I've seen that one.... ;)
http://www.network54.com/Forum/519893/thread/1164752966/big+bore+co2+valve (http://www.network54.com/Forum/519893/thread/1164752966/big+bore+co2+valve)
Thats a cool design did he ever build one? First time Ive ever seen it but I never go over there(Yellow)
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Don't think he did. Started a slightly different take on it and then ....nothing.
http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve (http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve)
Doesn't matter...I doubt it was the first time the idea rolled around, and doubt it'll be the last. We keep re-inventing the same wheel.
Al
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Don't think he did. Started a slightly different take on it and then ....nothing.
http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve (http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve)
Doesn't matter...I doubt it was the first time the idea rolled around, and doubt it'll be the last. We keep re-inventing the same wheel.
Al
Aint that a fact!!
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Travis, did that exotic valve in your pictures work? Did it close at all?
Looks interesting, but seems to me the benefit of the larger valve goes to flow obstructions around it?
Marko
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Don't think he did. Started a slightly different take on it and then ....nothing.
http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve (http://www.network54.com/Forum/519893/message/1165642350/revised+big+bore+valve)
Doesn't matter...I doubt it was the first time the idea rolled around, and doubt it'll be the last. We keep re-inventing the same wheel.
Al
I`m just throwing a 2 cent here and not going main Stream.. Would a Airforce valve reversed could be make with the port upward???
The normal usage of a popet valve is so that more surface of OBSTRUCTION is more difficult to move around .. The AIRFORCE valve due to it`s cylindrical empy core shape could manage that INSTANT airflow.. RIGHT??
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There is no point making a valve like that, it's not the stem that is so much of an obstruction, it's the 90 degree turn that cuts back flow.
Marko
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Alain, the stock Air Force valve is not "straight through", it has lots of corners for the air to flow around after the poppet.... Doug's aftermarket AF valve, not so much.... but they should all be called "axial-flow" valves, not straight through, as the air still has to flow around the head of the poppet....
Bob
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I took a break from tuning today to work on the Tactical version.... I measured up the length, selected a hole in the adjustment range of the AR style stock that would give me about 14.5" LOP, and then made the new end plug / stock adapter....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/AR%20Stock%20Adapter_zpscvrnbf3x.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/AR%20Stock%20Adapter_zpscvrnbf3x.jpg.html)
As always, I am astounded how long it takes to make a simple part from scratch, designing on the fly.... about 5 hours for this, believe it or not.... ::)
Bob
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I believe it. ;)
Al
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;) ;D Well what else can you do with 5 ft icicles hanging from the eaves and 3 feet of snow with arctic weather conditions except hole up in the shop and build stuff to play with when the weather warms up again ;D ;D
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Sounds like every other day of my life.
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I installed a taller sear from Lloyd in the PRod trigger group today and installed it on one of the tubes.... Since the PRod tube is thinner wall and smaller diameter, the sear would otherwise not project far enough through the Mrod sized tube to catch the hammer.... Once that was done, then I made a foregrip out of a piece of 1-1/4" ABS black plastic pipe.... It is just the right thickness to fit between the tube and the barrel, and I notched it around the receiver.... It fills the entire space between the trigger group and the drop block....
Here is what the Tactical version looks like with the PRod trigger group, the AR style stock, and the tubing foregrip.... I'm quite pleased with how it turned out....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tactical%20Version_zpsiuwntmwj.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tactical%20Version_zpsiuwntmwj.jpg.html)
As shown, with the 500 cc bottle (no regulator) it weighs 7 lbs. 3 oz.... I have never shot a Tactical style gun before, and beauty isn't exactly a strong point, IMO.... but the ergonomics are interesting.... I mounted a scope in Medium height rings, and the cheek weld is really solid and the perfect height for me, with the stock mount lined up with the center of the MRod tube.... That's nice, because that is how I made the mount, and it's a lot easier than making an offset one.... I find the high toe of the stock strange, compared to what I am used to, but the toe of the butt sits nicely in the pocket of my shoulder, so it is actually quite comfortable.... I can see the practicality of a Tactical stock, and how you could quickly grow to like it....
Bob
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Nice looking $100 adapter. I made lots of $50 bolts, $10 washers. The $500 paperweights are what gets me down. I have a bunch of music wire if you need some. Up to .055"
Steve
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That's nice Bob, good proportions the ergonomics should be good. Where's the balance point at?
Marko
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Might have to dig up a carbon bottle for my buddy. That would really cut the weight down.
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Balances within the foregrip....
Travis, you tease you.... *eyeroll*....
Bob
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Being one that likes the tactical look and feel, I must say Wow!! Very nice! Love the simplistic, straightforward look of it.
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Find it looks very similar to my bottle disco build in .25 cal pictured below ,the one in my avatar is in .22 .I used a pice of aluminium channel for a chassis ,it protects the regulator and gauge assembly. Because I'm using a QB drop down there are already holes in the block for the barrel band that helped with securing the chassis. The CAF infantry C7 rifle was the first rifle I ever shot so the feel is quite familiar to me ,and it shoulders easy. Not to mention the weight savings from not having a traditional stock.
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Today I made the cheekpiece for the wooden stock....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg.html)
It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....
Bob
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Today I made the cheekpiece for the wooden stock....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg.html)
It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....
Bob
Now that is Sexy looking
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Although I don't feel worthy to post on your posts AR stocks are outstanding for fire control, especially when it's time to rock and roll. It's funny when the first m16s where issued they where thought as a BB gun. But marksmanship increased.
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Today I made the cheekpiece for the wooden stock....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg.html)
It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....
Bob
Do you feel this one to be more balanced in the hand?? Nice piece of art...
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I haven't assembled the wooden one with a bottle yet, so can't comment on the balance....
After assembling the wood version with the .25 cal barrel and the Cothran valve, I decided to try some of the 41 gr. BBTs that I cast a week ago.... I tried some as cast, and they were a bit tough to load, they were better at 0.254", and at 0.253" you could feel them seat in the chamber, but you didn't have to push very hard.... I will test different diameters for accuracy at a later date, but for now I am using them sized to 0.253" for my Chrony work.... The hammer is the 28 gr. MDS hammer I made with the aluminum core and an adjustable striker.... I tethered the gun at 1900 psi, set the striker flush with the end of the hammer, and set the hammer spring preload to zero, and started testing.... I am still using the same spring, but without the SSG, so that I can adjust the striker through the middle of the spring and rear adjuster bolt....
I checked the velocity first with the 34 gr. JSB King Heavies, and it was 978 fps (73 FPE) as expected at this pressure... The first shots with the BBTs were 918 fps for the 41.7 gr. FN (78 FPE) and 938 fps for the 39.5 gr. HP (77 FPE).... Leaving the striker flush, I backed out the preload a turn with no change, and then 2 turns, and the velocity tanked.... I then turned the preload back in a turn, it was back to normal, and then I backed out the striker 1 turn below flush (recessed into the hammer).... The velocity was normal, so I backed it out another turn, and the gun did not fire.... The hammer is hitting the bumper on the back of the valve, and at this combination of preload and recessed striker, the valve is not opening at all.... I left the striker recessed, and started adding preload to the spring, and by adding a couple of turns I was able to get it to fire weakly.... After some experimenting with different settings, I decided to set the preload 1 turn out from zero (ie a slight gap between the hammer and spring), and to set the striker 1 turn below flush on the face of the hammer.... At this striker setting, the hammer is hitting the bumper when the valve is open about 0.070", and it really won't matter how much preload I add, it won't open further, at least in theory.... I am hoping that when I connect it back up to a bottle so that I can check the efficiency, I will have found an improvement, both from the heavier bullets, and from limiting the valve lift.... which may reduce the dwell slightly....
The experimenting I have done so far with an adjustable striker mirrors what happens with changing the preload.... Basically the valve is either cycling properly, or it isn't and falls off the cliff.... At 1900 psi the velocity with the 34 gr. JSBs is a bit higher than desired at 978 fps.... while these BBTs are a fraction lower than I want.... I would like to see the FN solids at just under 950 fps, and the HPs at just over, for a solid 80 FPE.... I think bumping the pressure to 2000 psi would do the job.... However, to get results I can compare to my previous ones, I will leave the 500 cc bottle regulated at 1800 psi for now.... and connect it back up for some efficiency testing....
Bob
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I did some measurements of the efficiency of the .25 cal version with the Cothran valve today.... I tethered the gun to the 500 cc bottle, with it regulated at 1800 psi, the same as I did previously.... I was using the 28 gram MDS hammer with the aluminum core and adjustable striker, and the same spring but without the SSG in place (so that I can adjust the striker), and the energy absorbing polymer (IsoDamp) bumper on the back of the valve.... With this setup the hammer stops when it hits the valve (bumper), and the amount the valve opens is dictated by the position of the striker, relative to the face of the hammer.... If the striker is flush, the valve can open about 0.108".... if the striker protrudes, it can open further (up to the 0.200" limit of the valve stem protrusion).... and if recessed the valve opens less (recessed 3 turns the valve can't open at all, no matter how much hammer spring you use).... With relatively light preloads, the valve quits opening if the striker is recessed about 2 turns into the hammer face.... ie the gun will not fire at all with the striker recessed more than 2 turns....
As I experiment with the adjustable striker, I am coming to some interesting conclusions about the Cothran Powerhouse valve (whether they are correct or not, I don't know).... I think the valve, once opened a small amount, and with enough backpressure in the exhaust port, "blows open".... From actual lift measurements I made on the Disco version, when cycling properly it opens about 0.060"-0.120".... while when it has fallen "off the cliff" it is opening about 0.020" or less.... Normally, a valve opens pretty much in a linear relationship to the hammer strike, the Cothan does not.... The interesting part is, that with the adjustable striker in this gun, I can get the valve to cycle reliably (providing I have enough hammer strike) with the striker recessed into the hammer face 1.5 turns, which in theory means it can only open the valve about 0.050".... Now perhaps the bumper is compressing, and the valve stem is getting pushed a few thou further, but I don't think there is any way it is getting to 0.060".... and yet the measurements I made with the Disco valve (which is identical inside) say that the valve is opening that far or more.... This has led me to the conclusion (unproven) that once the valve opens about 0.030", it blows open to provide twice that much actual lift.... Right or wrong, that is what I THINK is happening....
Like most valves, if you hit them way too hard, they waste air.... In my first tests with the Cothran valve, whacking it hard didn't produce any more power, but I could make the gun use up to 80 psi per shot, with an efficiency of less than 0.50 FPE/CI.... This is usually an indication that the valve is still open after the pellet has left the muzzle.... As you approached the cliff (from the plateau), the efficiency came up to around 0.65 FPE/CI, and then just before you got to the cliff it increased to just under 1.0 FPE/CI, using about 35-40 psi per shot with the 34 gr. JSB King Heavies.... I was curious what would happen to the efficiency using the adjustable striker to restrict how hard you could hit the valve, regardless of the hammer spring preload.... I wasn't disappointed....
If I set the striker so that it protruded 3 turns from the hammer face (the same thickness as the bumper on the back of the valve), then the bumper never came into play, and the valve acted just like it did before.... Whack it too hard, and the efficiency went into the tank.... When I set the striker flush with the hammer face, however, things changed.... In theory, the valve could only be driven open about half way, and that is exactly the way it acted.... That is far enough to deliver maximum velocity, but not enough to drive the valve so far open that it becomes an air hog.... No matter how much preload I used on the hammer spring, I couldn't get the gun to use more than 40 psi per shot.... Compare this to the 80 psi per shot it would use if you really whacked it before, and you realize that what the bumper does is stop the hammer before it opens the valve further than required, even if you use way too much hammer strike.... It's like having a "limiter" on the amount of air the valve can use.... This is obviously a very good thing, as it makes it extremely easy to not use way too much air.... However, 40 psi per shot is still not great for efficiency, it is only about 0.85 FPE/CI with the 34 gr. JSBs.... It was now time to explore what happened when you tuned closer to the "cliff"....
I now had the ability to approach the cliff in two ways.... I could do it by reducing the preload, or by reducing the initial valve opening, or both.... Believe me, I burned through a lot of pellets and bullets, and a tank of air, trying to figure out what was going on, and which worked better.... I tested with the 34.2 gr. JSB King Heavies, the 39.5 gr. NOE HPs, and the 41.7 gr. NOE FN.... Both the BBTs were sized to 0.253".... I determined that I could recess the striker as much as 1.5 turns into the hammer face and still have the valve cycle properly.... I tried various preloads with it set there, and with it set flush (and in between), and determined that all that happened was it took a slightly different amount of preload to reach the cliff, and the psi of air used for an 8-shot magazine didn't really change.... It was how far from the cliff you were that determined how much air you used.... However, I reasoned that the less lift I allowed with the striker (while still having enough to cycle the valve), the less sensitive the preload might be, and the less difference it would make in air usage if you used too much.... In reality, I don't think it mattered much, but I got some pretty decent efficiency numbers while operating in the 71-75 FPE power range....
Something else I discovered is that the BBTs used less air than the pellets.... I don't know if that is because they were tighter in the bore, heavier, and therefore building more backpressure, causing the valve to close faster, or some other effect.... but instead of 320 psi for 8 shots, they only used 280 psi.... and this was when operating up on the plateau, well above the cliff.... Since I was also getting 2-3 more FPE with the BBTs, this put their efficiency at over 1.0 FPE/CI, instead of under with the pellets.... As I backed off on the preload and approached the cliff, the pressure drop for 8 shots dropped to 270 psi for the pellets and 240 psi for the BBTs, while the velocity only fell off 2-3 fps.... There was about a 1/2 turn range of preload over which the change in velocity and air use was slight, making it much easier to tune just above the cliff, but with consistent velocity.... Here are the final results at 1800 psi....
JSB 34.2 gr.... 969 fps.... 71.3 FPE.... 1.00 FPE/CI
BBT 39.5 gr. HP.... 918 fps.... 73.9 FPE.... 1.17 FPE/CI
BBT 41.6 gr. FN.... 898 fps.... 74.7 FPE.... 1.18 FPE/CI
With the BBTs, I was getting a pressure drop on the 500 cc bottle of 240 psi for 8 shots.... With the regulator set at 1800 psi, that should work out to about 5 magazines (40 shots) at 75 FPE per fill (a total of 3000 FPE).... or about 35 shots with the JSBs at 71 FPE.... I am beginning to think that the Cothran valve is better suited to bullets than pellets.... and quite likely the heavier the better.... If I were tuning for the 34 gr. JSBs, I would probably reduce the setpoint to 1700 psi for 70 FPE.... while for the BBTs I would increase it to 2000 psi, where it should be a good, solid 80 FPE gun.... with a low ES and a decent shot count....
One thing for sure, anyone using a Cothran valve in an MRod might like to consider putting a couple of # 118 O-rings inside the tube, right up against the back of the valve (assuming a stock hammer with flanged, adjustable striker).... If you are using a hammer with a flush face, like the new WAR MDS hammer, a single one should prevent you from opening the valve so far that it will waste a ton of air.... If the valve is capable of opening 0.090" or so, it never needs to open more than that, from what I have seen.... The stem protrudes just under 0.200", so with an O-ring being 0.103" thick, and a flat faced hammer, you should never have to worry about opening the valve too far and dumping air after Elvis has left the building.... Playing with the preload to get close to the cliff and optimize the efficiency is all that would be left to do, once you get the pressure set to give the velocity you want with the pellet you are using....
Bob
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WOW!! Nicely done Bob... Back pressure is the added ingrediant that need to be add to the mix.. Gotcha!!
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This is exactly what Ive seen also Bob as the bullet weight goes up the efficiency gos up and this can be contributed to the poppet return orifice in the stem. Inside the poppet stem is a sliding metering rod that acts like a valve. Once high pressure air is introduced into said orifice it blows by metering rod and slams it closed thus preventing the back pressure from getting out then the trapped air forces the poppet closed. Now Don never intended the valve to be used in the manner in which we are trying to use it so POWER is what he was after and using a lot of air to get there. So the more back pressure (heavier bullet) you can produce the faster the valve shuts. So what Im doing literally right now is opening up that tiny .015 hole to .030 to introduce more back pressure and with a heavier return spring also I expect(hope) we will see a much more efficient valve for small bores. Don has been working with me every day and and having him on the team is awesome and having Bob answer my silly questions has saved me so much R&D time. We will get there Im sure of it.
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The backpressure acts in a strange way.... Without it, the valve won't cycle properly.... If you shoot a PCP with a Cothran valve in it, without a pellet, the valve doesn't open properly.... It needs that pressure in the exhaust port to open fully.... and then also uses it, flowing through that tiny vent hole, past the metering rod in the stem, to close again.... At least I think that's how it works.... *LOL*.... You can prove this to yourself by adjusting it to open properly, but near the cliff, with a bullet.... and then try a lighter pellet, and the valve barely opens....
I have a slightly different take on the efficiency.... I think the valve, at a given pressure, wants to release a certain amount of air, or saying it another way, stay open for a set amount of time.... If the dwell is a constant, the heavier bullet has moved less down the bore in the time the valve is open, releasing a smaller quantity of air (the lower psi drop I saw with a heavy bullet).... Now that air has more distance to expand in, creating slightly more FPE.... Less CI of air, creating more FPE, means a higher FPE/CI.... ie higher efficiency....
Bob
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Ok just got done with first string after drilling stem hole and this should be proof enough. I drilled it to .030. Thats and avg FPE/cuin per shot of 1.63 BY FAR the best I have had from the warp at this power level BUT some draw backs, it now closes fast and chops the power and needs higher reg pressure to get to previous power levels. Higher reg pressure leaves less head room but the report from gun is acceptable again!!! More testing to do.
Description: Warp 30
Notes 1: 3k 2200psi
Notes 2: Mod DC valve
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 50.00
Temp: N/A °F
BP: N/A inHg
Altitude: 0.00
# FPS FT-LBS PF
20 692 53.17 34.60
19 694 53.48 34.70
18 688 52.56 34.40
17 701 54.57 35.05
16 700 54.41 35.00
15 693 53.33 34.65
14 706 55.35 35.30
13 684 51.95 34.20
12 702 54.72 35.10
11 702 54.72 35.10
10 703 54.88 35.15
9 702 54.72 35.10
8 703 54.88 35.15
7 709 55.82 35.45
6 710 55.98 35.50
5 714 56.61 35.70
4 709 55.82 35.45
3 717 57.09 35.85
2 723 58.04 36.15
1 713 56.45 35.65
Average: 703.2 FPS
SD: 9.9 FPS
Min: 684 FPS
Max: 723 FPS
Spread: 39 FPS
Shot/sec: 0.0
True MV: 703 FPS
Group Size (in): 0.00
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Sounds like you have drastically reduced the dwell by drilling out the vent hole.... Problem is, it's a one-way street, go too far, and you need a new poppet.... I wonder if sanding down the metering rod would give you more control, and if you go too far, you just make a new one from a piece of 1/8" drill rod.... I guess it will depend on which is the restriction, the vent hole or the annular space around the metering rod....
Having to increase the pressure to get back to the same FPE sounds indeed like you have shortened the lift and/or dwell.... With the valve closing earlier in the shot cycle, you are releasing less air during the open cycle, and that air has more distance in the barrel to expand, helping get back some of the lost FPE, and increasing the efficiency.... It makes perfect sense, now all we need is to find a way to make that venting, and therefore the dwell, ADJUSTABLE.... ::)
I know you are using a stiffer valve spring, did you try the original spring with the drilled out vent hole?.... could be you could drop the pressure again?....
Bob
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Sounds like you have drastically reduced the dwell by drilling out the vent hole.... Problem is, it's a one-way street, go too far, and you need a new poppet.... I wonder if sanding down the metering rod would give you more control, and if you go too far, you just make a new one from a piece of 1/8" drill rod.... I guess it will depend on which is the restriction, the vent hole or the annular space around the metering rod....
Having to increase the pressure to get back to the same FPE sounds indeed like you have shortened the lift and/or dwell.... With the valve closing earlier in the shot cycle, you are releasing less air during the open cycle, and that air has more distance in the barrel to expand, helping get back some of the lost FPE, and increasing the efficiency.... It makes perfect sense, now all we need is to find a way to make that venting, and therefore the dwell, ADJUSTABLE.... ::)
I know you are using a stiffer valve spring, did you try the original spring with the drilled out vent hole?.... could be you could drop the pressure again?....
Bob
First thing tomorrow ill be putting back Dons stock return spring as like you said and I thought it may gain back the FPS and leave more head room and still allow for better efficiency. What Don and I are trying to do is make the valve more flexible across the spectrum. So hes willing to make changes to the valve as needed. Tomorrow Ill have more testing to do but i see the light at the end of thr tunnel. And on changing the metering rod well i did that and it caused all kinds of problems but ill call you tomorrow and explain.
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Bob,
I have experienced exactly the same results when adjusting the hammer strike and hammer spring preload that you are describing in reply#166.
My setup uses the same IsoDamp that I gave you, a stock spring, and an adjustable striker. The cross over point for opening the valve is a delicate balance, but after reaching that cliff, the valve seems to open fully all by itself. I was using a hammer of about 50 grams. I finally arrived at a spring preload of only .18" and a valve stem strike distance of only .027". In other words, the striker drove the valve stem only .027" before the hammer was stopped by the IsoDamp. The striker might have traveled a few thou more, but still, the amount that the stem needs to be "pushed" is minuscule. My gun uses a 20" barrel, and I found that even doubling the hammer preload and/or doubling the striker travel made almost no difference in power, but it did seem to use more air.
It was very interesting that when the preload and striker were adjusted to just barely fully open the valve, that shortening the striker distance by only .009", or decreasing the spring preload by only .015" would reduce the velocity by 400 fps, almost cutting the velocity in half.
Lloyd
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Nice to see your comments, Lloyd, I miss your input when you are busy with other things.... I agree that when you are on the cliff (falling over it), the velocity changes very rapidly with miniscule changes in preload or striker distance.... However, if it was just a matter of it being sensitive, I could live with that, and just figure out how to make tiny adjustments.... The problem is, that with the valve being so sensitive between 400-900 fps (ie while dropping off the cliff), I find the velocity to be totally inconsistent.... You can shoot 5 shots, and have two "normal" shots of over 900 fps, and the other three anywhere between 400-700 fps.... I have literally seen an ES of 500 fps within 5 shots.... This, of course, is totally unacceptable.... so I see little choice but to run the valve solidly on the plateau, but as close to the edge of the cliff as possible without falling over it....
Bob
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Nice to see your comments, Lloyd, I miss your input when you are busy with other things.... I agree that when you are on the cliff (falling over it), the velocity changes very rapidly with miniscule changes in preload or striker distance.... However, if it was just a matter of it being sensitive, I could live with that, and just figure out how to make tiny adjustments.... The problem is, that with the valve being so sensitive between 400-900 fps (ie while dropping off the cliff), I find the velocity to be totally inconsistent.... You can shoot 5 shots, and have two "normal" shots of over 900 fps, and the other three anywhere between 400-700 fps.... I have literally seen an ES of 500 fps within 5 shots.... This, of course, is totally unacceptable.... so I see little choice but to run the valve solidly on the plateau, but as close to the edge of the cliff as possible without falling over it....
Bob
I agree with this and making any FPE/FPS changes requires adjustment of pressure valve sees and just leave valve on the knee. The regulator is now your hammer spring adjustment per say as well as T-port changes to add or subtract back pressure to close valve. I find it much easier to find the knee using a limiter for valve over travel just like you and Bob have both done and using reg pressure to then get me to desired FPE.
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OK, I think I am FINALLY beginning to understand how the Cothran valve reacts to different setups and calibers.... I replaced the .25 cal upper with the .30 cal upper today, with NO other changes.... It was still tethered to the 500 cc tank with a regulated output of 1800 psi, and the striker is still set at 1.5 turns below flush on the hammer.... This means it drives the valve open about 0.050", although it may blow open further than that if it wants to.... I initially used the same 2 turns of gap between the spring and the hammer that I started with yesterday, loaded a magazine up with 7 of the JSB 50.2 gr. pellets, and fired a shot across the Chrony.... about 400 fps.... OK, I half expected it would need a harder hammer hit with the larger bore, so I added a turn of preload.... 930 fps.... GREAT, so now I know that there is hardly any difference in how hard you need to hit the valve with a .30 cal compared to a .25 cal.... That is quite different than a conventional valve, which usually requires a significantly harder hammer strike as you increase the caliber, to fill the larger barrel volume....
I topped up the 500 cc tank, leaving my Great White tethered to it with the valve closed, so that I could use the big gauge to read the pressure drop in the 500 cc (same as I have been doing with all these tests), shot a couple of shots to stabilize everything, recorded the pressure, cranked in 8 turns of preload, and shot a 7 shot mag. across the Chrony and recorded the new pressure.... It dropped 380 psi.... Bear in mind that similar tests without the striker recessed showed as much as 80 psi pressure drop per shot, so the recessed striker certainly saves a lot of air if you have wayyyyyyyyy too much hammer strike.... I backed the preload off to 4 turns, the velocity dropped only 3 fps, and the pressure drop for 7 shots was 300 psi.... I then set the preload to zero, still the same velocity and pressure drop, so the gun was acting exactly the same as it did yesterday with the .25 cal barrel on it, at the same settings.... even the same pressure drop, although this was for 7 shots (at 97 FPE) instead of 8 shots (at 71 FPE).... I then backed the preload out another turn (1 turn of gap, now), lost another 2 fps, but the pressure drop was now only 280 psi.... One more turn out (which worked fine with the .25 cal), and I was back down to ~400 fps, so I added 1/2 turn, and the valve was back to cycling solidly and reliably, at 926 fps (96 FPE), with only a 240 psi pressure drop for 7 shots.... This works out to 1.33 FPE/CI, a very respectable efficiency for a .30 cal gun at this power level.... I only needed 1/2 turn more preload in .30 cal than I did in .25 cal....
So to summarize, when set about 1/2 turn of preload above the cliff, so that the valve cycles solidly, reliably, and with low ES (well under 1%), and shooting pellets.... I am getting 8 shots in .25 cal at 71 FPE on 280 psi of air (1.00 FPE/CI).... and 7 shots in .30 cal at 96 FPE on 240 psi of air (1.33 FPE/CI).... In my Disco Double, at the same pressure, in .357 cal, I was getting 128 FPE at 1.53 FPE/CI (78 gr. pellets @ 862 fps).... I think it is pretty clear what is happening here.... The Cothran valve, when cycling properly but operating just above the cliff.... has a relative constant dwell, so providing the barrel is long enough that the valve is closing well before the pellet reaches the muzzle, it is dumping a relatively constant amount of air into the barrel.... Yes, it dumps a bit more into a larger bore, but relative to the bore volume, it is less, which means the valve is closing sooner in the larger caliber, leading to higher efficiency.... This behaviour also explains why we were getting such high FPE/CI numbers in .357 cal but pretty miserable numbers in .25 cal. and the .30 cal is right in between....
This leads me to a pretty obvious conclusion.... The Cothran valve is a way better choice for larger calibers and heavier bullets.... ie for high FPE applications.... However, as we gain a better understanding of it, we can tame it down for use in regulated PCPs as low as .25 cal....
Bob
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Bob,
I have observed the same phenomenon and definitely tend to agree with your conclusion.
I have also observed some super sensitivity in the distance that the striker drives the valve stem. For instance, (as in reply #173 above) when the spring and striker were set to barely, but fully, open the valve, turning the striker in 1/4 additional turn (.009) required that the spring ALSO be turned in by a larger amount, approx .025", to keep the valve opening fully. I don't really understand why it seemed to take disproportionate amount of additional spring preload to compensate for the increase in striker travel. A mystery.
Lloyd
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The AREA of a hole .015" and that of .030" is HUGELY different !!!
Frankly would have taken .005" or LESS incremental size enlargement steps to get a more definitive cause & effect graphed out.
JMO ....
Scotty
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I suggested the same thing to Travis, Scott.... I would start at stock (0.020") and go 0.002" at a time and graph out the results.... keep going until you either hit a straight line plateau, or the velocity was so low as to be useless....
Bob
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That would have been nice to do if I had steeped Carbide bits that small that could bore threw a rockwell 44 hardened valve stem. I used what I had and I can use pressure to verify the effects so no real need to chase 10 steps when I can just figure it out in 2-3 steps.
heres latest string with modded valve stem on warp with 12" barrel
Latest regulated run from 3k to 2100 Reg was set at 2200. I did get a flyer towards the end on shot 14 but like i say I dont sort or size I just pull from the tin and go.
Created: 02/02/17 08:19 PM
Description: Warp 30
Notes 1: mod TC valve 3k 2100
Notes 2:
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 50.00
Temp: N/A °F
BP: N/A inHg
Altitude: 0.00
# FPS FT-LBS PF
17 726 58.53 36.30
16 728 58.85 36.40
15 731 59.34 36.55
14 757 63.63 37.85
13 735 59.99 36.75
12 736 60.15 36.80
11 741 60.97 37.05
10 740 60.81 37.00
9 746 61.80 37.30
8 735 59.99 36.75
7 743 61.30 37.15
6 739 60.64 36.95
5 740 60.81 37.00
4 738 60.48 36.90
3 739 60.64 36.95
2 738 60.48 36.90
1 734 59.82 36.70
Average: 738.0 FPS
SD: 7.1 FPS
Min: 726 FPS
Max: 757 FPS
Spread: 31 FPS
Shot/sec: 0.0
True MV: 738 FPS
Group Size (in): 0.00
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Who Loves you Buddy ;D .... We're hopeless enablers seeking your efforts for our benefit ::)
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LOL. I still cannot get a good string with a 25 cal no matter what I try it just seems I cant get the dwell down low enough FRUSTRATING!!! AAARRRGGGHHH but I might try putting a sail on the stem or something Im running out of ideas fast. I have a lot of tricks up the sleeve but the sleeve is getting shorter and shorter.
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LOL. I still cannot get a good string with a 25 cal no matter what I try it just seems I cant get the dwell down low enough FRUSTRATING!!! AAARRRGGGHHH but I might try putting a sail on the stem or something Im running out of ideas fast. I have a lot of tricks up the sleeve but the sleeve is getting shorter and shorter.
All i can offer is Sarcasm ... absolutely clueless on balanced valve tech :-*
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Yeah, that's what I'm finding.... running out of tricks in the box of tricks.... need a bigger, deeper box.... ::)
Bob
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Don never intended the valve to be used on small bores or low power so were really trying to make his POWER valve tame and its proving hard to do really. I have just a few more tricks then Im done trying and will use a self regulating valve for the small bores and Dons for the big bores. I wouldnt actually call Dons valve a balanced valve its actually a hidden poppet valve as there is no equal force that balances out the opening if that makes since.
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Oh, it's balanced, all right.... The "force reduction piston" fastened on the front end of the valve subtracts it's area from the area of the poppet seat.... Only the difference in the two areas is holding the valve closed.... That is why it's so much easier to open....
Bob
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Oh, it's balanced, all right.... The "force reduction piston" fastened on the front end of the valve subtracts it's area from the area of the poppet seat.... Only the difference in the two areas is holding the valve closed.... That is why it's so much easier to open....
Bob
Thats what I'm saying it's hiding the poppet and reducing the poppets picture to the pressure but isn't balanced it's force reduction not using balanced pressure but that's how I see it as opposed to having equal or near equal pressure pushing back or in balance. A true balanced valve doesn't get harder to open with more pressure it stays constant as pressure is opposing. Either way it works well.
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OK, so your opinion is that a "balanced valve" must be 100% balanced, and only held closed by the spring?.... I guess that is one interpretation.... Using that definition, then the balanced valves that Lloyd and Tom use, and any of the other designs I have seen (including the Cothran) are "semi-balanced".... I would respectfully submit that a 100% balanced design (like a symmetrical spool valve, with equal pistons both ends) has zero chance of ever being self-regulating.... so I would prefer a "semi-balanced" design where the opening force is still proportional to the air pressure (just much reduced).... so that we have a chance of it being self-regulating....
Bob
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That is not what I said at all your misinterpreting what I posted but it doesnt really matter anyway lets get on to business. Im going to pull Dons valve again and try a few different things today and see If I can get the dwell short enough for a light bullet. Fingers crossed as this may be my last attempt unless I dream up something else soon.
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.. I would respectfully submit that a 100% balanced design (like a symmetrical spool valve, with equal pistons both ends) has zero chance of ever being self-regulating.... so I would prefer a "semi-balanced" design where the opening force is still proportional to the air pressure (just much reduced).... so that we have a chance of it being self-regulating....
Bob
Not to interfere in your developper brainstorm, but i`m really interested in what you just say there Bob.. SO!! BY DEFENITION=A balanced valve would have a spool valve with equal piston at both end.. Can someone elaborate in this mather???? I`m really interested of KNOWING what is happening with this type of valve.. Thanks guys..
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To visualize a spool valve, think of a spool of thread in a tube with two open ends.... One end of the tube is the barrel, and there is a side port in the tube supplying HPA, that when the valve is closed is in between the two ends of the spool.... Since there is equal pressure on both ends of the spool, it has no end force and happily sits there, and no air moves from the side port into the barrel....
Through the hole in the middle of the spool is a piece of string, hanging out the other end of the tube.... To fire the valve, you give a tug on the string.... As soon as the other end of the spool clears a small part of the side port, there is now air pressure on the barrel end of the spool, which forces it fully open, emptying the HPA reservoir out the barrel....
Without some other mechanism to close, or reset the valve, it dumps ALL the air in the reservoir in one shot.... That is how a basic spool valve works....
If the two ends of the spool are different diameters, then when you pressurize the middle of the spool, you create a force on the spool towards the larger diameter.... This can be used to hold the valve closed against a seat.... Instead of having the HPA between the ends of the spool, you could also have the pressure on the ends, and the exit (exhaust port) in the middle.... kind of an "inverted" spool valve.... but the concept is the same.... To fire such a valve, you need to overcome the force holding the spool against the seat....
In a conventional poppet valve, the force against the seat is the area of the seat, times the air pressure (plus any valve spring)..... In a spool valve, the force against the seat is the DIFFERENCE in area between the seat and the balancing part of the spool, times the air pressure.... You are using air pressure against one end of the spool to reduce the force against the seat at the other end.... and therefore reducing the hammer strike required to open the valve.... When I talk about a "balanced valve", I would almost always be referring to one that is "semi-balanced" where the spool reduces, but does not completely eliminate the force holding the valve closed.... because if the balancing force is equal (or greater), the valve will usually become a "dump valve" and will lose any capability to self-regulate as the pressure changes....
If you want to see an example of a dump valve, triggered by a smaller pilot valve.... look at Reply #61 here.... http://www.gatewaytoairguns.org/GTA/index.php?topic=119234.60 (http://www.gatewaytoairguns.org/GTA/index.php?topic=119234.60) .... In the case of the Lane Cartridge, the spool valve is larger at the balancing end, and once the small HPA chamber on the back side of it is dumped, the spool moves back under the influence of the internal pressure, dumping all the air in the cartridge....
HTHs....
Bob
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Thanks for the precision.. I will wrap my head around it more... That bring a new perspective in my knowledge and understanding of some principal behind the heart of the pcp..
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Today, after much prompting by Travis, I started modifying my Cothran valve, to try and improve it's efficiency in my .25 cal regulated BRod.... It is important to realize that these changes may not work (in fact are unlikely to work) in an installation that is prone to hammer bounce.... In my gun, I have an energy absorbing bumper made from "Iso-Damp" on the back of the valve, an extremely light MDS hammer of only 28 grams, a recessed striker that only pushes the valve stem about 0.050", and an SSG.... This allowed me to consider removing the small metering rod (counter-piston) which lives inside the valve stem.... There is a debate as to the purpose of that device, but I believe it to be to prevent the valve from re-opening on a second, or subsequent hammer strike, by acting as a "leaky check valve", slowing the HPA that fills the poppet head during the cycling of the valve from dumping back too quickly into the exhaust port.... I have been told that removing it will cause everything from uncontrollable hammer bounce, to various burps or flutters, to extreme air use, to even destruction of the valve itself.... However, since Travis agreed to supply me with any parts I destroyed I decided to remove it.... I tethered the gun at 1900 psi and started testing.... What happened?.... Exactly NOTHING.... Zip.... NADA....
The valve functioned exactly as before, the same velocity, sound, air use, everything.... I was shocked, but it does reinforce my belief that its primary purpose is anti-bounce.... which I have already addressed by a combination of four different methods.... I did notice one thing that changed, if I leaned on the hammer strike by adding preload (instead of gap) to the SSG.... thereby vastly overdriving the hammer.... the velocity DROPPED slightly, accompanied by a high-frequency "flutter".... I don't know how else to describe it.... It sounded like hammer bounce, but much faster.... The strange thing was, it didn't use more air.... As I said, removing the metering rod may not work in many installations, if they have any possibility of hammer bounce.... but in my gun, set up the way it is, it made no difference, when the SSG was adjusted normally, with a bit of gap.... The velocity was stable until you got to the cliff, and then dropped like a stone, same as always....
OK, so the other thing Travis (and others) have tried is drilling out the tiny vent hole in the valve stem.... This hole lives in the exhaust port, and allows the hollow head of the poppet (which is the diameter of the "force reduction" piston attached to the front of the valve) to be at atmospheric pressure between shots.... This "blanks off" the equivalent area of the poppet, drastically reducing the opening force required to crack the valve.... When you fire the gun, the pressure in the exhaust port rises, HPA flows through that hole, through the valve stem (past the metering rod) and pressurizes the inside of the poppet, providing a greatly increased closing force for the valve.... Without this vent, the valve would stay open, and likely vent the entire reservoir.... With it, the valve cycles in a timely manner, allowing lots of air to escape and produce copious amounts of power.... The way Don builds the valve, I would estimate the dwell time at roughly 2 mSec.... and if you have way too much hammer strike, it can be even more.... Limiting the valve lift keeps that more constant, preventing the valve from being a real air-hog, which is why I like that modification....
In stock form, that vent hole is tiny, only about 0.020".... Logic dictates that enlarging it will make the valve close faster, reducing the dwell.... and that should lead to increased efficiency.... The stem is HARD, and Travis warned me not to try drilling it, and I didn't have small enough drills anyways.... so I did like he did, and used a thin pointed diamond burr in my Dremel and "countersunk" the hole, gradually opening it up at the same time.... The smallest diameter, doing it this way, is just at the very inside of the vent hole, and I found I was causing tiny burrs inside the stem, which I had to keep cleaning out with a #31 twist drill (0.120"), turning it by hand.... I did this in case I had to drop the metering rod (0.118" diam.) back in the hole, I didn't want it to get stuck.... Anyway, I used a couple of sewing needles with the points ground off as go-nogo gauges, and when one that was 0.028" would fit through the hole (but one measuring 0.030" wouldn't) I quit grinding.... I chose 0.028" because it has TWICE the area of the original hole.... I have no idea it that is optimum, but I wanted to start smaller than what others had used, which was 1/32" (0.031") or larger.... I left the metering rod out, reassembled the gun, and repeated my testing.... All I can say is WOW !....
First of all, it took a bit more hammer strike to open the valve.... not a lot, but a couple of turns less gap on the SSG.... Secondly, instead of a completely flat plateau, with only a few fps drop just before you got to the cliff, and then nothing.... I actually saw a "knee" on the curve.... It wasn't long, the sensitivity to SSG gap was still there, but compared to stock it was day and night.... Here are my results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Valve%20Modded_zpstkjwkdua.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Valve%20Modded_zpstkjwkdua.jpg.html)
Note that the blue (stock) and black (no metering rod) lines virtually lie on top of each other.... At 3 turns of gap on the SSG, the velocity is at maximum, at 4 turns, it has only dropped a few fps, and shortly after that the velocity became unstable (400-500 fps ES) and at 5 turns out it was in the basement.... With the larger vent hole, compared to the velocity at zero gap, there was about a 10 fps loss at 1 turn out, and then about another 15 fps in the next turn.... At 2 turns of gap, the velocity was 25 fps below the peak, and the ES was still less than 1%.... At 2.5 turns of gap, the average velocity dropped another 40 fps, to what in a conventional valve would be the middle of the knee, but the ES had increased to about 2%.... At 3 turns of gap, the velocity was down 200 fps, but the shots were all over the place, with an ES of over 5%.... The valve was becoming unstable, although nowhere near as bad as a stock one.... At 4 turns out, the valve was no longer cycling properly, it was in the basement....
I then tethered the gun to my 500 cc bottle, regulated at 1800 psi, for some efficiency testing.... I left the bottle connected to the gauge on my Great White (valve closed) so I could record the pressure drop for a 8-shot mag. and tested each half turn out, starting at zero gap.... At that setting, the velocity was maximum for this pressure, at 968 fps, and the drop 280 psi, for 0.97 FPE/CI.... This was basically the same as I had before, with the 34 gr. JSB Heavies.... At 1 turn out, the velocity was 962 fps (220 psi) and 1.22 FPE/CI.... At 1.5 turns, 951 fps (210 psi) and 1.24 FPE/CI.... and at 2 turns of gag, 943 fps (200 psi) and 1.28 FPE/CI.... This is far better efficiency than I have ever had before with the Cothran valve in my .25 cal BRod.... At 2.5 turns out, the velocity (809 avg.) was becoming unstable, and it was much worse at 3 turns out (701 fps), so I didn't record the efficiency, figuring it was meaningless....
So, what are my conclusions?.... Well, for one thing, if you have cured all chance of hammer bounce, I think you can try removing the metering rod, I don't think it is necessary.... Secondly, doubling the area of the vent hole, by increasing the diameter to 0.028", decreases the dwell at a given hammer strike, and creates the beginning of a knee to the velocity vs preload/gap curve.... It gives you significantly more control of the velocity just above the cliff, and softens the cliff into a usable, although sensitive knee.... While the operating pressure is still by far the dominant factor in the velocity, you can now detune the velocity just a bit, saving air in the process.... I haven't got all the answers, but I think we're on the right track....
Bob
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Excellent work as usual and I'm confident that if you make the hole slightly larger .035-.040 and put the pin back in but upside down with a spring below it you will get to 1.50 efficiency. The rod is in there to fill the area above the poppet without it the lock time(dwell) increases due to HP air feeding threw a small hole at high speed then spews into a big void slowing and filling the area now with the pin in it fills up all that void and having the spring in there also fills in the area and also the rod doesn't have to move and this adds to lock time. So put pin in upside down with very small spring below holding pin up and your dwell will again be cut in half and your ES and effecincy will both be much better and it will add another 50 FPS of adjustment below the knee.
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Even at 1.28 FPE/CI is a respectable number.. If ever Travis is right, at 1,50 FPE/CI would that be one of the most efficient valve out there??
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I am pretty happy to get 1.28 FPE/CI at 68 FPE, or 1.22 FPE/CI at 70+ FPE.... particularly from a 23.8" barrel at only 1800 psi.... Remember that the higher the FPE output, relative to the barrel length and pressure, the tougher it is to get great efficiency numbers.... If I reduce the dwell more, then I will also, automatically, be reducing the velocity, and have to increase the pressure to make up for that to get back to 70 FPE.... The increase in efficiency will have to come from a higher setpoint, which means less overhead (pressure range between fill pressure and setpoint).... which will eat into shot count.... The choice then becomes simply a matter of how much air you have to put into the tank to top it up, not how many shots you can get.... I should currently be on track for about 48 shots at 68 FPE, or about 44 shots at 70 FPE, per fill.... :o .... If I raise the setpoint to 2000 psi, I will need to increase the efficiency to 1.46 - 1.54 FPE/CI to break even.... If I have to increase it to 2200 psi to make up for the reduced dwell, I would need 1.83-1.92 FPE/CI to get the same shot count.... I have my doubts, but I've been wrong before.... ::)
Bob
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Yes youll lose a little headroom but you wont have to move your reg pressure that high I believe. I dont mind loosing a few shots to get better efficiency as it lowers the guns report and thats a big concern for me, I know your running with no shroud or moderator so for you the lower set point and higher shot count is probably a better set up. Also the higher reg pressure will also reduce dwell as well so for me its a win win but for you maybe not so much. You should try just for posterity reasons.
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Bob, thanks for performing that test. It's always nice to get some confirmation. It does seem that a larger vent will help close the valve faster... improving the self-regulation.
Your .028" vent sounds good for HPA. The vent I'm using for co2 is .031" - makes sense that the vent for HPA should be smaller.
I'm glad I found this thread - had no idea from the title. Well done!
Wyo
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I would like to try and come up with a combination for the Cothran valve that will work in both .25 and .30 cal, regulated at 2000 psi or less.... and shooting heavy pellets in the mid 900s.... with the option of shooting slightly heavier bullets without having to get rid of the regulator.... I know, dream on !!
Bob
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Today I pulled out the Iso-Damp bumper I had, and substituted a #210 90D O-ring.... I did this because ANYONE can find one of those.... I set the striker FLUSH with the end of the hammer, because then you don't need an adjustable hammer, Travis' new MDS hammer with the flat face would work fine.... The hammer I was using was still very light, at only 28 grams, and I was still running the SSG.... I measured the distance the hammer can push the valve stem with the #210 O-ring in place, and even pushing on the hammer very hard, it only pushes the valve stem 0.075".... I think this is right in the sweet spot, the valve opens plenty far enough, but you can't drive it so far that it becomes an air hog.... I haven't tried this at 2900 psi, but at 1900 psi, it is SIMPLE and works GREAT !.... There was NO change in the settings required with the 0.028" vent hole and no metering rod, the performance was identical to with the Iso-Damp....
This afternoon I put the metering rod back, with a small spring under it, as Travis suggested.... I had it small end down, and the spring was from a Crosman 13XX Safety..... It went coil-bind just before the valve stem went flush with the valve, but that is about 0.100" past where the hammer stops.... Basically there was almost no difference compared to running the valve with no rod at all, running tethered at 1900 psi.... The vent hole was still 0.028", and the peak velocity was a about 10 fps lower at zero gap on the SSG, and also at 2 turns of gap.... At 2.5 turns out, the velocity was about the same as with no rod, but the ES was a bit worse.... At 3 turns out, the velocity was actually 13 fps higher than with no rod, and the ES had increased to over 150 fps over 4 shots.... Not only did I not see an increase in the adjustability of the valve between maximum and the cliff, I was seeing greater instability in velocity than without the rod at all.... I was not at all happy with the way it was performing with the metering rod in place, so I took it back out....
For the next tests, I increased the diameter of the vent hole to 0.0345" (ie between 0.034-0.035"), which TRIPLES the area of the original 0.020 hole in the stem.... I did not use the metering rod.... With the gun once again tethered at 1900 psi, I immediately noticed both a drop in velocity, and a decrease in the report.... I tested hammer spring settings from 8 turns of preload, through zero gap on the SSG, to 4 turns of gap, where it fell off the cliff.... Here is the results, plotted on the same graph I posted yesterday....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Modded_zpsbh1t0nsv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Modded_zpsbh1t0nsv.jpg.html)
There are a couple of things to note.... Although I didn't bother to plot it, once I added preload to the hammer spring I noticed the same high-frequency "fluttering" sound I heard yesterday, and with the larger vent hole, it was accompanied by a significant DROP in velocity.... The more preload I cranked in, the lower the velocity got, until at 8 turns of preload it was just over 900 fps.... While not a huge loss, there was no way I could get to the nearly 990 fps velocities I was getting with the same ports, at the same pressure, before I started enlarging the vent hole.... I think this is proof positive that enlarging the hole reduces the valve dwell.... I did NOT try removing the O-ring so that I could drive the valve to greater lift, I don't know if that would move the plateau up again.... but I am pretty sure that doing that would burn a lot more air.... Note that the velocity with the 0.035" vent hole actually peaked at 1/2 turn of gap on the SSG, and fell off both sides of that.... This is completely different than the way the Cothran valve was designed to work.... At 2 turns of gap, the ES had increased to over 50 fps, and at 3 turns of gap it was over 100 fps.... At 4 turns the valve had fallen off the cliff, as expected....
I then tethered the gun to my 500 cc bottle, with an 1800 psi regulated output, to check the efficiency.... I only shot two 8-shot strings, one at the maximum velocity setting of 1/2 turn of gap, and the other with 1.5 turns of gap, where the velocity was still stable.... All I was interested in was comparing the efficiency to what I had with the 0.028" vent hole.... At the higher setting, I got an average velocity of 921 fps (64.4 FPE) and an ES of 1.29 FPE/CI.... With 1 turn more gap, that dropped to 908 fps (24 fps ES at 62.6 FPE) at 1.25 FPE/CI.... Basically, I was getting the same efficiency as with the smaller vent hole, but at 5 FPE less power.... not exactly a great trade-off, IMO.... Yes, I could increase the pressure to get the power back, but I really doubt I would see enough of an increase in efficiency to make up for the decreased pressure headroom.... In this gun, in .25 cal, and at these pressures, IMO I have increased the vent hole too much....
Ohhhhhhhhhhhhh Travis.... I need a new poppet.... *LOL*....
Bob
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New poppet on the way. can you run one more string with large vent hole and rod in upside down at same settings this will either confirm or make me look at another angle after long barrel testing tomorrow.
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Will do.... send pellets with poppet, please.... J/K.... ::)
Bob
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As Travis requested, I ran another test today, with the 0.035" vent hole and the metering rod in place, upside down, with the small spring under it.... The rest was unchanged from the previous tests, I was using a single #210 90D O-ring as a bumper, with a flush front on the 28 gr. hammer, and the SSG.... The gun was the .25 cal. version, shooting 34.2 gr. JSB King Heavies, tethered at 1900 psi.... I started at zero gap, and checked the velocity over 4 shots, at each 1/2 turn of adjustment out from there until the valve fell off the cliff....
The results were pretty much as I expected.... The rod restricted the filling of the cavity in the poppet head somewhat, and the gun acted more like it had the 0.028" vent hole without any rod in place.... The velocity was slightly less at zero preload, peaking at 1 turn of gap at 975 fps, and then declining slowly to 2 turns, after which the velocity dropped quite quickly.... It did fall in a more linear fashion over the next turn of adjustment before hitting the basement at 3.5 turns of gap.... I was not at all happy with the ES, however.... It was great while the velocity was on the plateau at 970 fps, but as soon as the velocity started to drop, the ES increased.... At an average velocity of 958 fps, at 2 turns of gap, the ES over just 4 shots was 17 fps (2%).... At 2.5 turns of gap, the average velocity was 872 fps, but over 4 shots varied between 751 - 933 fps (20%)....
I tethered the gun to my 500 cc tank, regulated as before at 1800 psi, and ran one 8-shot string to check the efficiency.... It used 210 psi, producing an average velocity of 953 fps (69 FPE) with a 17 fps ES (1.8%) over the 8 shots.... This is an efficiency of 1.25 FPE/CI, basically unchanged from previous results at that velocity....
The greatest range of adjustability I achieved during these tests was with the 0.028" vent hole and no metering rod in place.... I had a solid 20-25 fps range over which the efficiency was over 1.2 FPE/CI, coupled with a low ES.... It was the closest thing to a conventional "knee" I have been able to achieve with the Cothran valve.... The only way to really adjust the velocity remains changing the pressure.... but that setup allowed me to decrease the velocity below the normally flat plateau the Powerhouse valve displays by up to 25 fps, accompanied by a decrease in the amount of air used.... Trying to tune further below the plateau, with any of these "improvements", resulted in unstable operation and a high to unusable ES....
I am going to try the 0.035" vent version (without rod) at 2900 psi with a heavier hammer.... and also plan to do some testing with it with the .30 cal top end.... once I top up my Great White....
Bob
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I don't recall reading about anyone reducing the size of the force reduction piston. I guess you would have to sleeve the piston bore and make a new piston. I don't know how difficult this would be, or if it could be done at all.
Dons valve opens with a light hit, so some of the force reduction could be sacrificed to make the valve behave more like a conventional valve, and still not need a crazy striker spring. No?
Maybe reduce the area of the force reduction piston 30% or even 40% and see what happens.
Steve
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I'm sure what you are suggesting COULD be done.... the problem is in keeping everything concentric, because the poppet is mounted in one end of the valve and the force reduction piston in the other.... I can't imagine it's too easy to make them with the degree of accuracy required in a home shop.... You would have to sleeve the inside of the poppet, or make a new one, as it is the "cylinder".... Lloyd ad I have have talked about this, and it could well be the way to get some degree of self-regulation....
I just made a new "metering rod" from a piece of 3/32" brass rod 0.80" long.... The idea is to simply take up as much of the volume inside the stem as possible, without causing any restriction to the airflow between the vent hole and the chamber inside the poppet.... It is a loose fit inside the stem (0.094" rod in a 0.120" hole, so it "meters" nothing) but it's 0.10" longer than the original metering rod, so it barely fits with the poppet fully open.... I figure it can't really hurt, so I may as well try it....
Bob
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This evening I got a chance to do a little bit more testing.... I used the .25 cal version with the Cothran valve, with the 0.035" vent hole, but this time I put a 0.8" long piece of 3/32" brass rod inside the valve stem instead of the metering rod.... This is a loose fit, so it won't restrict the HPA entering the head of the poppet, but it will take up a lot of the volume inside the stem.... It is longer than the metering rod by 0.10", and the lenght just clears when the poppet is full open.... I also put the 51 gr. MDS hammer (with steel core) back in, so I did 2 things at once, not the best situation, but I'm running out of the 34 gr. pellets.... I tethered the gun at 1900 psi, determined where zero gap was on the SSG, and shot a couple of shots at each gap setting, increasing the gap until the velocity went over the cliff.... The velocity was pretty much stable, although the ES was poor, until I got to 4.5 turns of gap, when it started to decline, slowly at first, and then rapidly, falling over the cliff at over 6 turns of gap.... The velocity curve was quite similar to what I got with the metering rod in place with the spring, except it moved out 3 turns on gap, which would be due to the heavier hammer.... I tried one string tethered to my 500 cc bottle at 4.5 turns out, and 8 shots averaging 938 fps (67 FPE) used 220 psi of air, which is 1.16 FPE/CI, not quite as good as before....
I then tethered the gun at 2900 psi, and repeated the testing of velocity vs SSG gap.... At this higher pressure, I just nicely had enough hammer strike with the 51 gr. hammer.... I was able to max. out the velocity at 1/2 turn of gap on the SSG, just about perfect.... and the velocity was only 10 fps less than what I got in the very first tests with the valve in stock form.... With the 0.035" vent, however, there was some adjustment to the velocity before the velocity plummeted.... I didn't do enough shooting to determine what the ES was like, just a shot or two at each setting.... but it looks like the larger vent does pretty much the same thing to the curve at 2900 psi as it does at 1900 psi.... It would require a lot more testing to determine the optimum vent hole size at this higher pressure.... and the fact that I was down slightly on velocity tells me that the 0.035" hole is a bit too large.... I'm guessing that if I remove the 3/32" spacer rod, the dwell (and the velocity) will drop a bit more.... I may try that tomorrow....
Bob
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OK, today I used the Cothran valve with the 0.035 vent hole and no rod inside the stem.... I still like not having the rod in place, providing you have some method of completely preventing hammer bounce.... The unobstructed flow through the vent hole into the cavity in the poppet seems to provide the smoothest knee, and the tightest ES, IMO.... However, don't expect much usable range of velocity adjustment, you still need to do 95% of that with the pressure.... All the larger vent hole does is provide you the ability to approach the cliff more slowly and under more control.... The combination of a larger vent hole, and no hammer bounce, produces better efficiency.... The larger the vent hole, the shorter the valve dwell, and if you go too big, you will have to increase the pressure to get back the velocity you lose.... With the .035" vent hole, I am losing about 20 fps in the .25 cal. and about 30 fps in the .30 cal. at 1900 psi.... but gaining in efficiency....
I used my 51 gram MDS hammer with the steel core.... This additional hammer mass gave me back most of the velocity I lost when I went from the 0.028" vent hole to the 0.035" one.... This combination is the only one I have found where I can tune for both 1900 psi and 2900 psi, in both .25 and .30 cal, with just the SSG gap, and still have some gap at the higher pressure and yet get to the plateau.... I shot a few shots at each SSG gap setting with the 34.2 gr. pellets in the .25 cal at both 1900 psi and 2900, and did the same with the 50.2 gr. pellets in the .30 cal at both pressures.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20035%20Vent_zpsndvpcmm5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20035%20Vent_zpsndvpcmm5.jpg.html)
The .25 cal is in red, and the .30 cal is in blue.... The solid lines are at 1900 psi, and the dotted lines are at 2900 psi.... As you can see, the .30 cal requires about 1 turn less gap than the .25 cal.... At 2900 psi, you need 3 turns less gap than at 1900.... At the higher pressure I tried a couple of turns of preload (negative gap), and the gun got VERY loud (as expected) and the velocity fell off slightly.... I think that may be due to the O-ring bumper compressing with the heavy hammer strike, and kicking the hammer back slightly faster, reducing the dwell.... I also had something interesting happen with the .30 cal with 2 turns of preload.... The valve went into full auto mode, and completely dumped the 80 cc plenum, firing like a machine gun.... I would suspect that was due to removal of the metering rod, combined with too hard a hammer strike bouncing off the O-ring.... It certainly shows what can happen when you start modding a well-developed product, trying to make it do things it was never designed to do.... YOU REMOVE THE METERING ROD AT YOUR OWN RISK !!! .... Don't even think about doing that unless you have a hammer stop, and a lightweight hammer and springing system that won't bounce.... My guess is that had I still had the Iso-Damp bumper in place, its energy absorbing qualities would not have allowed this to happen....
I also tethered to my 500 cc bottle, with its output regulated to 1800 psi.... I only tested one SSG gap setting in .25 cal, and one in .30 cal, picking a velocity that was just on the low side of the plateau, at the very beginning of the knee.... The reason for that choice, was that as you approach the knee, the ES starts to increase.... This is a consistent effect with the larger vent hole, I think is what is happening is that the valve is becoming unstable when you ask it to operate where it was never designed to.... It can't make up it's mind whether to cycle properly, or to fall over the cliff.... Try as I might, I have not been able to find any combination of vent size and metering rod that produces stable velocities when you tune on the knee.... The only choice I have found, to keep a tight ES, is to tune to the point where the velocity is just starting to fall, at the bottom of the plateau.... This is in reality the same as tuning a stock valve near the top of the cliff.... the difference is that with the larger vent hole, you have less dwell, and greater efficiency, and the SSG gap adjustment is a lot less fussy.... ie it is easier to find the right spot.... Here are the results of the efficiency testing at 1800 psi....
.25 cal. 34.2 gr. JSB @ 4.5 turns of gap.... 946 fps (68 FPE) on 210 psi of air for 8 shots, which is 1.23 FPE/CI.... (should be 46 shots per fill = 3128 FPE total)....
.30 cal. 50.2 gr. JSB @ 3 turns of gap.... 909 fps (92 FPE) on 215 psi of air for 7 shots, which is 1.43 FPE/CI.... (should be 40 shots per fill = 3680 FPE total)....
Note that the shot count is projected from the pressure drop for 1 magazine, and is therefore only approximate.... It is based on a 3000 psi fill, and the 1800 psi setpoint (1200 psi of headroom).... The exact setpoint pressure and velocity and pellet used will affect the shot count, of course.... I tried the 44.8 gr. JSB .30 cal pellets, and they shot about 35 fps faster, with slightly lower efficiency.... I didn't do any testing with BBTs today.... I am pretty sure that I am going to set both BRods up regulated, with Cothran valves, in their final configurations.... Providing they prove to be accurate, it is my intention to increase the pressure slightly for the .30 cal to move the 50 gr. JSBs up closer to 950 fps.... A 2000 psi setpoint should do that nicely, trading off some efficiency and shot count to get closer to the 100 FPE mark....
Bob
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I also had one flutter hard and I pulled the valve today and seen the valve seat was almost destroyed this also was running with no pin. I'm looking at the parts and I believe this isn't hammer bounce as I was running a light hammer but unregulated. I think and don't quote me on this but I think the hammer slams down fast and bounces off valve seat. Anyway Don warned me about this and he was correct so please DoNot remove pin. I also went back to a smaller bleed port at .030 and it's working very good. Or another possibility is with the large volume of air in the stem with no pin the air doesn't evacuate fast enough causing a strange imbalance inside stem. Not sure but it's not safe
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Travis sent me a replacement poppet for my Cothran valve, as I think I went too far with the 0.035" vent hole.... because I lost some of the peak velocity.... I tried this one with the stock 0.020" vent hole, but with no metering rod, and it acted normally.... The velocity on the plateau (.30 cal. 50 gr.) was the same as stock, ie removing the metering rod didn't change it.... I had no strange effects like hammer bounce, but remember, I am running a #210 90D O-ring on the back of the valve to limit how far the hammer can drive the stem to about 0.075".... and the O-ring then stops the hammer, absorbing any excess energy.... However, with the small 0.020" vent, the valve was back to being "on or off", with a flat plateau and then a sudden cliff, losing the small amount of adjustment you can get with a bigger vent....
I had previously tried a 0.028" vent hole, which worked fine, and then increased it to 0.035", which IMO is too big, because I lost velocity on the plateau.... I think this means that I cannot get enough dwell to max. out the power.... Both the previous sizes were achieved by a pointed burr in a Dremel, which is difficult to get to the correct size, requiring that you keep checking the hole with a piece of wire of the diameter you want.... A couple of days ago, in a local Home Hardware, I saw some Cobalt twist drill that were 1/32" (0.031"), which is in between what I had tried, so that is what I used to enlarge the hole in the new poppet.... Travis had told me that the shaft of the poppet was very hard, and to grind it with a Dremel.... but I picked up a pair of these drills (they were $6.49 for 2) in the hopes that the cobalt steel would be hard enough to do the job.... I used the smallest collet in my Dremel, and ran it at the lowest speed (still probably 5000 PRM), and it drilled the hole out perfectly.... You have to be careful not to break such a small drill, but it was a lot easier to do than using the pointed burr, and the hole will be the same size, every time....
I was very pleased with the results.... I haven't lost any of the peak velocity on the plateau with the 1/32" vent hole.... This compares with a 35 fps loss with the 0.035" hole.... I haven't yet had the opportunity to see how much of an adjustment range I can get with this size.... ie what the knee looks like.... but I'm sure it will be similar to the 0.028" hole, which gave me some degree of adjustability before the steep dropoff.... Plotting that curve, and checking the efficiency on it, will have to wait for another day....
Travis, I'm not getting any flutter or anything else strange happening without the pin, running the #210 - 90D O-ring and a flush hammer face, which gives me about 0.075" of valve lift.... providing I have any gap at all in the SSG....
Bob
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The first trials with the new stem with the 0.031" (1/32") vent hole were a bust.... I removed the metering rod, and over a matter of a few shots at 2900 psi the velocity started to drop.... I had to keep increasing the hammer strike, and even that wouldn't put me back to where I started.... I pulled the valve apart, and found that the seat had a deep groove in it.... I can only assume that by removing the metering rod the valve was closing with such force it destroyed the rather soft seat on the poppet.... Either that, or there was a leak in the force reduction piston O-ring, which put a lot more force on the poppet.... I don't know why I never experienced this with the original poppet, it was still in good shape.... The solution was to disassemble both poppets and build one good one from the two sets of parts....
The poppet is made in three pieces, the hollow stem, the seat, which looks like a nylon washer, and the tubular front part, which is the sleeve of the force reduction system....The two metal parts are threaded together using 10-32 threads and glued, which make the poppet difficult to take apart without scarring the surfaces.... By using the two chucks on my lathe, and turning the headstock backwards by hand, I was able to take the poppets apart.... I used the new stem, with the 1/32" vent hole, and the old seal, turned over to use the flip side, which was perfect, and one of the front sections.... I reassembled it with a drop of blue Loctite and let it cure overnight before assembling and pressurizing it.... It sealed up perfectly first try.... I had installed the stock metering rod, and set about testing it....
As I found previously at 1900 psi, the velocity was right back up to where it was with a stock vent hole.... In .25 cal, there was very little adjustability, basically a plateau and a cliff.... In .30 cal, there was a slight rounding of the edge of the cliff, but the valve was still rock stable just above the dropoff.... With 70 gr. bullets, I did lose a few fps, so there is some indication that this is the largest vent hole you can use in .30 cal at this pressure without losing performance.... I would not go larger, because with the 0.035" vent I lost about 20 fps.... I did some short strings (1 magazine) tethered to my 500 cc tank with the output regulated at 1900 psi, and the efficiency was slightly better than with either the stock vent hole, or with the 0.035" vent, so I think I hit the sweet spot for the vent size, at least when regulated at 1900 psi.... Here are the results....
.25 cal. 34.2 gr. JSB.... 987 fps (74.0 FPE) @ 1.00 FPE/CI, with an ES of 13 fps....
.25 cal 46.4 gr. Cast RN.... 878 fps (79.5 FPE) @ 1.04 FPE/CI, with an ES of 7 fps....
.30 cal 44.8 gr. JSB.... 971 fps (93.7 FPE) @ 1.11 FPE/CI, with an ES of 12 fps....
.30 cal 49.3 gr. Daystate.... 949 fps (98.6 FPE) @ 1.17 FPE/CI, with an ES of 12 fps....
.30 cal 70.0 gr. BBT.... 824 fps (105.7 FPE) @ 1.35 FPE/CI, with an ES of 11 fps....
The .25 gr. pellets required 6 turns of gap on the SSG, the .30 gr. bullets required 5 turns, and the other three all were shot at 5.5 turns of gap.... I can probably get a bit smaller ES by using a lighter hammer, a weaker hammer spring, or a bit less preload on the SSG, to reduce the gap.... I was running the 51 g. MDS hammer with the steel core....
I then took the gun all apart, stripped down the valve, and replaced the metering rod with one I had sanded down 0.003" smaller.... I had heard this was something worth trying, and it produced some interesting results.... First of all, it created a curve where the plateau used to be.... With no gap in the SSG, the velocity dropped about 15 fps with the .25 cal 34 gr. JSBs, and about 40 fps with the .30 cal 50 gr. JSBs.... It then increased until there was 3 turns of gap, and then curved downwards to about 6-6.5 turns and was in the basement when 7 turns out.... I think the lower velocity at heavy hammer strike may be because of the hammer bouncing off the rubber O-ring, although why it should show up only with the undersized metering rod, I have no idea.... The total adjustment range between peak velocity (at 3 turns) and when it rolled over to head into the basement was about 100 fps, so I was quite excited that I would finally be able to get some adjustment in velocity with the Cothran valve without having to play with the pressure.... Unfortunately, for nearly all of that 100 fps range, the velocity was unstable, with the ES increasing as you approached the cliff.... In other words, with the undersized metering rod, I got a slight knee, but not a usable one, as the ES quickly became unusable.... Just before the velocity took a dive, the ES could be as much as 130 fps from one shot to the next.... I fiddled with it, trying various adjustments, but could never get the ES as low as with the stock metering rod, so I took the gun apart and put the stock rod back inside the valve stem....
I tried a few more tests with the stock metering rod and the 1/32" vent hole, and I am very pleased with this combination at 1900 psi.... As long as you stay just above the cliff, in the area where the velocity is 10-20 fps below the maximum at that pressure, you are rewarded with a narrow ES, lots of power without maximum report, and decent efficiency.... I don't think there is anything I can do to get a better tuning range than I have for the Cothran valve, in .25 or .30 cal, when regulated at 1900 psi....
Bob
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Sounds about right to me. Have you tried running at a lower FPE to see if the Efficiency goes up? Or do you see a pretty similar efficiency across the spectrum?
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The only way to really do that is to reduce the pressure, so no, I haven't done that.... If I reduce the velocity the ES goes up....
Bob
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I took a few shots today tethered at 2900 psi, with the following results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%202900%20psi_zpsm0blqx5z.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%202900%20psi_zpsm0blqx5z.jpg.html)
As you can see, the pellets that were in the mid 900s at 1900 psi are Supersonic at 2900.... I tried some heavier bullets, sized down to fit, and the biggest surprise was the 66 gr. in 25 cal breaking 120 FPE.... I have a feeling that the enlarged vent hole in the stem is hurting the performance of the 109 gr. in .300 cal, as I would have expected more FPE from it instead of less.... After all, the porting is the same as my DAQ, which shot over 180 FPE with the same bullet at the same pressures.... If you correct for my shorter barrel lengths, my .25 cal is about on a par with Lloyd's original experiments with the MRod with the Cothran valve, as is the 80 gr. bullet in the .30 cal, but the 109 gr. is lagging.... It could also be the O-ring bumper on the back of the valve that I have used to limit the hammer travel, I have, after all, done several things to throttle back the valve to work better regulated at 1900 psi.... I guess it's not to surprising that some or all of those changes have combined to knock the top end off the power at the top end.... in fact it would have been surprising NOT to see that.... ::)
Bob
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Are you guys using any lubing on the cothran valve internals, on the o-ring inside the poppet/valve stem end especially? My valve was acting little sticky and I took it apart to clean it. Now I'm wondering to lube or not. I don't know if the o-ring was installed dry in the first place, but it sure looked like it was dry. And can anyone tell the o-ring sizes and type for the Mrod valve, I'd like to get some spares.
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The force reduction O-ring would be a #006 (1/4" OD x 0.070").... I don't know the material, but mine was translucent/white, so likely Urethane, but I don't know the Durometer (90 is the most common).... I always use a small amount of Dow 55 on all O-rings on installation.... and this should be even more important in a sliding application, IMO....
Bob
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Yes it looked like urethane o-ring. I quess Ultimox will work on it.
I think the sticky feeling on the valve stem was due to valve stem biting in to the brass center. It's like something is trying to push the valve stem sideways alittle bit. Are you seeing any of this on your valve?
By the way Bob, could....... you........ fix....... your....... keyboard..... as..... as..... informative....... your.......... posts............ are............., they.............. are.......... f*****g............ annoying............. to................... read................ for.................................. some......................................reason.....
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Jari..................................................... I don't see anything wrong with my keyboard............................................................................ sorry.... :P
The front piston should be free to move sideways slightly on the valve.... that makes it self aligning....
Bob
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Just have to read between the ........................ easy peasy......
Mike
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Ok ok it makes power lets see how they shoot. ;D
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I know it has been a while since I posted in this thread, but summer is an impossible time for me to work on airguns because the Motel is too busy.... During the winter, I worked with Travis and Jim designing an adjustalbe regulator to go inside their drop down tank block.... I just received one in the mail today, and it is gorgeous....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg.html)
I got both tank adapters, one for 5/8"-18 UN threads, and one for 18 mm x 1.5 mm threads, so I can use any tank.... The burst disc is on the output side, and is a 3K, as I won't be using more than about 2200 psi.... However, I understand the output can be adjusted higher than that, depending on the Bellevilles installed....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg.html)
It has room for two gauges, the upper one reads output pressure, and the lower one tank pressure.... The adjusting screw is an allen set-screw on the bottom of the block.... It moves the HP seat towards the piston (CW) to reduce the output pressure and away from the piston (CCW) to increase it.... I can't wait to try it out on the tube I have the Cothran valve installed in.... It will be the perfect arrangement for that, because you must adjust the pressure to adjust the velocity....
Bob
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Those look awesome! Very excited to see the results!
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;) Looking good Bob Can't wait to see some results . How can it be busy I thought you only had three guests a year in the busy season way up there in the middle of nowhere ::) ;D
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;D
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That would be three rooms full, almost every day, right now.... all my wife and I can do to keep up....
Bob
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I know it has been a while since I posted in this thread, but summer is an impossible time for me to work on airguns because the Motel is too busy.... During the winter, I worked with Travis and Jim designing an adjustalbe regulator to go inside their drop down tank block.... I just received one in the mail today, and it is gorgeous....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg.html)
I got both tank adapters, one for 5/8"-18 UN threads, and one for 18 mm x 1.5 mm threads, so I can use any tank.... The burst disc is on the output side, and is a 3K, as I won't be using more than about 2200 psi.... However, I understand the output can be adjusted higher than that, depending on the Bellevilles installed....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg.html)
It has room for two gauges, the upper one reads output pressure, and the lower one tank pressure.... The adjusting screw is an allen set-screw on the bottom of the block.... It moves the HP seat towards the piston (CW) to reduce the output pressure and away from the piston (CCW) to increase it.... I can't wait to try it out on the tube I have the Cothran valve installed in.... It will be the perfect arrangement for that, because you must adjust the pressure to adjust the velocity....
Bob
This will have many love from people out there.. I`m one of them.. ;D
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This project has been on the shelf over the summer, both for lack of shop time and because I have been waiting to received one of the new ART/SS valves to try.... The hope is that it will match the Cothran, both in performance and ease of opening.... with the added benefit of being able to adjust the velocity with hammer strike, something you can't do with the Powerhouse valve.... you have to change the pressure to change the velocity.... Anyways, the wait is over and my valve arrived today, many thanks, Travis.... 8)
The valve is a stock JSA "SS Balanced Valve" as they supply for the MRods.... It comes with a 3/16" exhaust port and the stock recess for the transfer port, which would not work in my BRods, as they are set up for a 3/8" OD transfer port with a 1/4" exhaust port.... Travis assured me that there was plenty of meat to enlarge the ports, and there certainly was.... I usually angle my exhaust ports about 20 deg. but with that big a port and no experience with this valve, I choose 15 deg. instead, and I'm glad I did.... At 20 deg. with a 1/4" port, I think I would have broken into the back of the valve and ruined the seat.... The valve throat is 0.281", which works out to the same area, once you subtract the 1/8" stem, as the 1/4" exhaust ports.... This is the same size throat as what I had on my modded MRod valve with the PEEK poppet, but the area is smaller than the Cothran valve.... I didn't want to drill out the throat at this time, but I did blend the new 1/4" exhaust port into the throat with a spherical Dremel burr.... There is certainly lots of port area for lots of flow....
I got the valve installed in the tube for one of my BRods and it seems to be holding pressure.... I will leave it overnight and plan on doing extensive testing tomorrow, tethering the gun at 1900 and 2900 psi in both .25 and .30 cal to get the baseline preload curves and assess what the opening forces are like compared to the Cothran valve and my modded MRod valve.... This should be FUN !!!
Bob
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Super interested in the results.....
Most importantly the hammer weight,spring rate or force, and efficiency. Definitely would like to know how much you shoot below reg pressure before the valve/hammer bounce) runs away "if it does" and pulls a pressure dump.
Almost forgot to ask what port/jet size is being used in the valve.
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Here is the first set of results for my BRod .30 cal with the ART/SS valve installed.... I tethered it at 3000 psi (a more accurate, digital gauge says my regulator was not set for 2900 as I previously thought), and tried the 50 gr. JSB/Daystates and also the 67 gr. NOE BBTs.... I tried all the SSG settings from maximum preload (way too much), through zero gap, to 10 turns of gap (over 1/2").... I then repeated the procedure with the 45 gr. JSBs and 50 gr. JSB/Daystates tethered at 1900 psi.... Lastly, I connected up my 500 cc bottle which has a regulated 1900 psi output and shot one 7-shot magazine of the 50 gr. pellets at several gap settings to find the pressure drop and calculate the efficiency.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20Gap_zps5icyu4tb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20Gap_zps5icyu4tb.jpg.html)
First some comments about this valve.... IT OPENS EASILY.... nowhere near the hammer strike required of my modded MRod valve.... I will be doing the same testing procedure with my Cothran valve to get an idea of the relative hammer strike required, but don't have that data yet.... It is much more responsive to changes in hammer strike than the Cothran, although still exhibits a VERY sharp velocity drop if you try and tune it for tiny sips of air (ie low velocity).... This sudden drop could well be due to the jet size installed in the inlet of the valve, I only got one with the valve, presumably a "stock" one, whatever that is.... and I can tell you it's pretty tiny.... With that tiny jet, and the huge drilled out exhaust port, I may be operating the valve outside its normal parameters.... in fact you can almost bet on it.... I hope Travis has some ideas to try and will send me some other jets to play with.... not that it really matters, I never tune my guns on the downslope anyways.... If I wanted a lower velocity, I would reduce the regulator setpoint and move back up onto the knee of the curve....
I am using an MDS hammer with a 3/4" steel core that weighs 51 grams.... The hammer spring is 0.48" OD x 3.00" long, and is made of only 0.051" wire, so has a spring rate of just 8 lb/in.... It is currently set up on the SSG with 0.60" of preload (4.8 lbs.).... and when set to zero gap, with the hammer stroke I have of 0.79" takes a maximum force of only 11 lbs. to cock the gun.... If you notice from the data in the graph, I can run the SSG gap at about 6 turns out (0.33") at 1900 psi (cocking force 8.5 lbs) and about 3 turns out (0.165") at 3000 psi (cocking force under 10 lbs) with hardly any velocity loss.... Those settings are basically at the top of the "knee".... With the 50 gr. pellet at 1900 psi, at 6 turns out, the velocity is 922 fps (94 FPE) and the efficiency is 1.04 FPE/CI.... The knee is quite long and gentle, making velocity adjustment quite insensitive, until you approach the "cliff".... Just before you get there, the velocity seems to get unstable, and the ES increases.... and then suddenly you are teetering on the edge of the cliff, where just a quarter turn more gap and the velocity tanks to under 400 fps....
The maximum performance (plateau velocity) with this valve is a few fps better than my modded MRod valve or the Cothran valve at 1900 psi.... and virtually the same with the 67 gr. BBT at 3000 psi.... but with the 50 gr. pellet at 3000 psi it was about 30 fps faster (1100 fps).... However, it also had virtually no velocity drop as you increased the SSG gap until it suddenly fell off the cliff.... almost acting like a Cothran valve.... However, this is so far out a normal condition (50 gr. pellet at 1100 fps) it doesn't really matter.... it's more an anecdote.... One other thing of note.... If I reduced the SSG gap to negative (ie introduced preload) the air consumption, report, and recoil all went "stupid".... I can only assume that the closing forces on the balanced poppet are so small that they are overwhelmed by the 5 lbs. preload on the SSG, and it increases dwell to the point the valve is still wide open when the pellet leaves the muzzle.... and YES, it's THAT dramatic.... When I was testing the pressure drop with 2 turns of preload, I actually got 640 psi of drop in my 500 cc bottle in just 3 shots.... compared to 370 psi drop in 7 shots with zero SSG gap.... Pretty much BOOM when you pull the trigger, complete with 6" or more of muzzle jump.... :o :o
The 8 lb/in. spring is OK for use at 3000 psi, but realistically I need to either reduce the preload on the SSG, or fit an even weaker spring for use at 1900 psi.... The SSG gap is too large at that pressure, and I might find a velocity difference shooting up or downhill from gravity slowing the hammer.... This change would make the gun even easier to cock, which seems silly, as it's sooooooooo easy now.... I can tell you, I'm SURE impressed at the reduction in cocking force with the ART/SS valve.... Travis and Lloyd sure came up with a winner here.... I can see that I will end up converting all my Big Bores and bullet shooters over, to get rid of the massive, long stroke, hard to cock hammers.... Incidently, I resized a 109 gr. Lee HP in .308 cal down to 0.300", and although it was still hard to chamber, I got 811 fps with 2 turns of preload (159 FPE) at 3000 psi.... accompanied by a huge roar and muzzle jump.... Yes, this valve can move a LOT of air....
Bob
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Here is the data for the .25 cal BRod using the ART/SS valve.... The methodology was the same as for the .30 cal.... except the pellets used were the 25.4 gr. Kings and 34.1 gr. King Heavies at 1900 psi and a 52.7 gr. RN .25 ACP bullet at 3000 psi.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20ART-SS%20Gap_zpsriqobzml.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20ART-SS%20Gap_zpsriqobzml.jpg.html)
The SSG gap where the gun fell off the cliff was virtually the same at the same pressure, about 7 turns at 3000 psi and 9 turns at 1900 psi.... I was using the same hammer and spring, all that changed was the upper (receiver and barrel).... This gun drives the Kings way too fast, nearly Supersonic at 1900 psi, but the King Heavies look to be a great choice at this pressure.... At 7 turns of gap (just over 3/8") the velocity is 966 fps (70.7 FPE) but the efficiency is a bit low, at only 1.01 FPE/CI.... Still, this is pretty impressive performance at only 1900 psi, and should yield about 32 shots at 70 FPE from the 500 cc bottle.... nothing to sneeze at....
As a bullet shooter at 3000 psi, the gun is solidly over 100 FPE, peaking at 115 FPE.... This is the highest FPE (by a whisker) I have seen with the .25 cal BRod at this bullet weight, and with a 60 gr. bullet would be even higher I am sure.... I didn't do any efficiency testing at that pressure, as I am short of cast bullets at the moment, and don't want to stop testing to make more.... Once again, if you crank in actual preload on the SSG, the gun roars and kicks as it blows air out the muzzle after the bullet is long gone.... It appears obvious that this valve (at least with the big ports) needs either an SSG or SSS to have any chance of behaving in a civilized manner.... It does offer some range of velocity adjustment, and the efficiency, like the Cothran valve, is best when operating just above the cliff.... However, with the ART/SS valve, that range is a lot broader and easier to tune to....
With the ART/SS valve using a 1/4" exhaust port, my BRods will be great with pellets when regulated at 1900 psi.... and are capable of shooting with bullets in both calibers at 3000 psi.... I'm pretty pleased with the results for initial testing.... I do need to try less preload on the spring to try and reduce the gap on the SSG, particularly when regulated.... I hope to get to that soon....
Bob
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That's some great power Bob. I know you'll wring out even more out of it.
I know you're using a longer barrels but assuming you were running this on 20" barrel with just a hair over 7/32 barrel port and valve at .250 TP, .300 throat and .047 jet on a stock Synrod tube with no depinger; how close to a 100fpe would one come after having the chance to play with the new ART valve? Curious as to what I'm seeing happening in my quest to relearning this valves behavior. Thanks.
Peter
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Same question here.
Great info.
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At 1.40 efficiency and the FPE you are at, this is now one of the best hunter I have seen... Those cast bullet are a major candidate for long shot and the energy they are at right at the top of the food chain.... BRAVO for the update and results..
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I reassembled a BRod with the Cothran valve this afternoon just to assess the comparison between the required hammer strike with it and the ART/SS valve.... To my surprise, the new ART/SS valve was easier to open than the Cothran.... :o .... Even with the preload reduced to only 0.40" (3 lbs.), the Cothran valve fell over the cliff at a 3 turn smaller gap than the ART/SS valve, with the same pellet at the same pressure.... Now BOTH these valves are a LOT easier to open than a conventional PCP valve of the same dimensions.... That is the big advantage to balanced valves, you can use huge ports, throat and poppet, and not have to end up with a gun that is impossible to cock....
I rechecked the Cothran valve, and it remains stubbornly "ON" or "OFF".... You really have no control over the velocity with the hammer strike, you need to change the setpoint pressure to do that.... Yes, the Cothran valve uses less air when tuned just above the cliff, but it cant be turned down a bit before it ceases to cycle properly and the velocity drops to near nothing.... It is when operating just above the cliff that the ART/SS valve can be tuned for good efficiency while remaining stable (unless you get too close to the cliff, as mentioned earlier).... That region with the Cothran valve is very narrow, and when you get close to the cliff the velocity becomes unstable, although if you get it just right, it also exhibits improved efficiency.... It is just way fussier to adjust than the ART/SS valve....
To make large adjustments to the velocity with the ART/SS valve (at least in my large ported version) you still need to alter the setpoint pressure.... However, having a 100-200 fps range of adjustment without changing the pressure sure makes it easier to find a suitable tune.... It seems that the heavier the bullet, the wider the velocity adjustment range.... I suspect that with a stock ported ART/SS valve the adjustment range might be even wider.... It looks like I may have to find a weaker spring to reduce the SSG gap down to the desired level when running regulated at 1900 psi.... but before I make that change, I think I will completely remove the front jet and see what happens....
Bob
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Peter, I don't know how the jets affect this valve, nor do I have any to play with.... You gun will be limited by the 7/32" barrel port (I am using an oblong port).... I'm surprised that you can run that big a port on a .25 cal without loading problems.... Also, you will be needing to run a bolt probe of 3/32" just to keep the chamber open enough to match that barrel port.... My .25 cal barrel is a LW 23.8" Polygonal, and I got 115 FPE with a 53 gr. bullet at 3000 psi.... You should be tickling 100 FPE with a stock 20" barrel at the same pressure.... but we're not talking a bell-curve starting at 3000 psi and ending at 2500.... but a single maximum power shot at 3000, and then descending velocity as the pressure drops....
Yes, Alain, nothing much wrong with 890 fps with the 34.1 gr. Heavy (60 FPE) at 1.42 FPE/CI on only 1900 psi.... That should be 50-55 shots on 500 cc from 3000 down to 1900.... 8)
Bob
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Peter, I don't know how the jets affect this valve, nor do I have any to play with.... You gun will be limited by the 7/32" barrel port (I am using an oblong port).... I'm surprised that you can run that big a port on a .25 cal without loading problems.... Also, you will be needing to run a bolt probe of 3/32" just to keep the chamber open enough to match that barrel port.... My .25 cal barrel is a LW 23.8" Polygonal, and I got 115 FPE with a 53 gr. bullet at 3000 psi.... You should be tickling 100 FPE with a stock 20" barrel at the same pressure.... but we're not talking a bell-curve starting at 3000 psi and ending at 2500.... but a single maximum power shot at 3000, and then descending velocity as the pressure drops....
Yes, Alain, nothing much wrong with 890 fps with the 34 gr. Heavy (60 FPE) at 1.42 FPE/CI on only 1900 psi.... That should be 50-55 shots on 500 cc from 3000 down to 1900.... 8)
Bob
Ok. The 7/32 barrel port doesn't interfere with loading my 55gr slugs but I can't speak for pellets as I don't shoot them in this particular setup. Also, I'm running a Gen 1 modded bolt for flow so it shouldn't be too restrictive I don't think. I ordered a few jets to play with as the one I received just was not cutting it at all. Currently I'm running a 0.0417 size jet and I can barely hit 89fpe without dumping 200psi per shot. Alternating between a stock spring and a ten pound spring with different weight MDS hammers and fill pressure. My previous ART valve was able to get me 97fpe Max but with a heavy spring(17lb). I do understand barrel length plays a part but I seem to be going backwards. Hopefully, you can get a few more jets to play with to compare all the variables.
Peter
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The 55 gr. slugs are probably long enough to easily bridge the barrel port, so they can't fall in while sliding past....
My jet is a # 87.5.... It is a loose fit on a 1/32" (0.03125") drill.... so I will take a guess that the numbers are 1/100ths of a mm.... because 0.875 mm = 0.0344".... I just pulled it out, leaving about a 1/8" hole, and will test that in the morning....
From my limited experience, running any preload against the hammer when uncocked may lead to excessive air use.... It certainly does with my SSG, even with only 3 lbs. of preload, once I run negative gap (ie preload) the gun gets LOUD and kicks like a mule.... I have seen it use over 200 psi per shot from a 500 cc bottle once there is preload.... It has blown the diffusers right off my Chrony, I mean I'm talking BIG TIME DWELL....
Bob
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Yes. No problem loading them at all. Smooth as butter.
That's the size ports mine came with. 87.5=0.0370inches. I'm currently running the 100=0.0417inches. I worked my way up to that size and was just having issues with the dwell/stability with zero pressure on the valve stem. I was thinking my issue was jet sizes being parallel to hammer weight and strike but it was just all over the place and unstable on various strings with same psi refill and same settings. However, after reading this(reply#19), https://www.gatewaytoairguns.org/GTA/index.php?topic=137844.msg1382081#msg1382081 (https://www.gatewaytoairguns.org/GTA/index.php?topic=137844.msg1382081#msg1382081)
It summed everything up.
Peter
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Today I tested the ART/SS valve without any jet on the inlet side.... just about a 1/8" hole there.... I still had the preload on the 8 lbs. hammer spring on the SSG set to 0.40" (about 3.2 lbs).... I tested the .30 cal version with the 50 gr. pellets at 1900 psi (only), and realistically there was no significant difference with the jet removed.... The valve still took very little hammer strike to open it.... So, I then swapped out the MDS hammer with the steel core (51 grams) for one with an aluminum core that only weighed 27 grams.... For some unexplained reason I lost about 10 fps from the maximum velocity (which I would not tune for, it would be too inefficient).... but as expected I now needed less SSG gap to get to the cliff.... Here are the results, compared to where I started with this valve (black line)....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20%20No%20Jet%20Gap_zpsbm6ecxjy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20%20No%20Jet%20Gap_zpsbm6ecxjy.jpg.html)
Changing to the 0.40" preload from 0.60" is what moved the top of the cliff from 9 turns of gap to 8 turns.... I didn't plot that curve because it essentially tracked the black line except for the earlier cliff.... You can see that with no jet installed (purple line) there was less of a "knee" to the curve.... still some, but there was less velocity adjustment before you got to the cliff.... The same setup but with the 27 gram hammer (the orange line) shifts the cliff to only 5 turns of gap, but I can still reach the plateau with 1 turn of gap.... This gives me an adjustment range of 4 turns, and makes the amount of gap where I would adjust the gun just about where I like to see it.... around 1/8"-3/16".... The only way to reduce it further would be a lighter hammer spring, or reducing the hammer stroke.... I can actually DO that with the aluminum cored hammer, as it has a steel setscrew insert for the striker (currently set flush).... One other thing I noted with the very light hammer.... The range of velocity adjustment between plateau and cliff increases significantly.... leading me to believe that light hammers and this valve would be a great combination....
I did one "efficiency run" by shooting one 7-shot magazine with the velocity set to just over 900 fps with both setups.... Small changes in the exact velocity make big changes in the efficiency at around that velocity with these big ports.... but essentially I believe there is little difference in the efficiency if the velocity is the same with the jet removed.... HOWEVER, it does give you less velocity adjustment just above the cliff, and if you are tuning for efficiency I think you would struggle to get the best combination of power and air usage without the jet.... If all you are interested in is pure power with a light hammer strike, however.... this valve is a BEAST.... It requires MUCH less hammer strike than even the Cothran Powerhouse valve in the testing I have done so far.... I'm impressed.... 8) 8) 8)
Bob
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Super interested in the results and the data collection.
Say, I would really like to put your SSG settings and valve jet size into minitab for a 2 level factorial design to see if it can predict what would be the best setting (jet size and ssg setting) for a desired power level and efficiency.
I think you have enough data collected for me to run predictions. I would be looking for a fixed caliber with a High/low SSG setting and High/Low jet size. Looks like you have the jet size High/low and the SSG setting High/low.
If you can or would, is there a chance you can hook me up with a table so I can run the numbers. If so, and if the program works, I may be able to map the valve at any SSG setting,jet size, for any power level and or efficiency.
If not, that's ok too. Thanks in advance
Like this:
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If you had the time to change the transfer port too, that would really change the mapping for everyone (I think).
3 factorial design
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Great Idea Tim. I was working on something similar with Excel but unfortunately I made and error that is all my fault and its been corrected I made the valve to easy to open and it became unstable with preload so Im sending everyone new internals that will allow for as much preload as you want without using tons of air when pre-loaded . So for now until the new internals are out this will be not really good to chart in mini tab or Excel as all the data will be changed. Sorry guys. Still the data Bob collected is awesome and will be similar except for spring the jet sizes will be different for the new internals. Your really getting some BIG power Bob from a low pressure thats for sure.
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I am here if you need it Travis. As you can tell, I am itching to by a valve.
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I don't fully understand what you need, Tim.... Looking at any settings with preload on the spring (negative gap) are useless, because the efficiency is about 0.2 FPE/CI, accompanied by horrendous report, recoil, and muzzle jump.... The only useful data would be where the plateau starts, down to where the cliff is, IMO.... In addition, I have been testing two calibers, and several weights.... I have a reasonable amount of velocity vs preload data, much less efficiency data, because my stock of pellets is running low....
According to Travis, any jet size over about 0.050-0.060" won't make any difference, it will react the same as removing the jet completely.... so again, pretty hard to map something when those datapoints are out of the useful range....
Bob
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Travis, this valve is so easy to open I don't care that I can't run preload.... as I would run either an SSS or SSG with this valve, period.... Since I already have an SSG built for the BRods, they will never see preload, and in fact even small gaps are useless unless I run a 27 gram hammer and only 3 lbs. of preload on my 8 lb/in. spring.... From what I understand the "correct" internals will require a bit more hammer strike than the one you sent me.... which is no big deal.... so both should work.... Of course they WILL give different data in terms of required hammer strike....
Looks like I'm going to have to order more pellets, though.... ::)
Bob
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That's Ok Bob. Sometimes I don't make sense right off the bat (or ever).
The numbers in the table were just made up from me from limited data (none of it makes real sense). It's better to run a DOE with numbers that are around the area you want to use so it can be optimized. Most importantly 2 tests, 1 wide open then one with the numbers closer.
Anyway,
I was looking for what makes the most interaction between the three factors. The program can simulate that like this. The numbers are just made up but gives the idea of what it can do.
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That's Ok Bob. Sometimes I don't make sense right off the bat (or ever).
The numbers in the table were just made up from me from limited data (none of it makes real sense). It's better to run a DOE with numbers that are around the area you want to use so it can be optimized. Most importantly 2 tests, 1 wide open then one with the numbers closer.
Anyway,
I was looking for what makes the most interaction between the three factors. The program can simulate that like this. The numbers are just made up but gives the idea of what it can do.
I really like that Tim and could be very useful in the near future.
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Well the data is non-linear once you hit the plateau velocity.... and that velocity is dependant on barrel length, pressure, SD, and port size.... For all my current data points, the barrel length is fixed, and so is the port size (within each caliber).... I have data for two pressures, and a few different weights (SD).... Here are some relative data points....
.25 cal - 23.8" barrel - 0.234" minimum port diameter (chamber minus probe) - barrel volume 19.15 cc....
.30 cal - 25" barrel - 0.257" port diameter (exhaust & transfer ports) - barrel volume 28.97 cc....
Pressures used 1900 psi and 3000 psi, constant pressure (tethered to regulator)....
.25 cal tested at 1900 psi with 25.4 gr. and 34.1 gr.... and at 3000 psi with 52.7 gr....
.30 cal tested at 1900 psi with 44.9 gr. and 49.7 gr.... and at 3000 psi with 49.7 gr. and 67.2 gr....
Initial setup 8 lb/in spring at 0.60" (4.8 lbs.) preload on the SSG guide.... later changed to 0.40" preload (3.2 lbs.).... SSG is 18 TPI (0.0556"/turn).... Initial ART/SS jet size # 87.5 (which I understand is 0.0344").... later removed, leaving a hole of about 1/8" (anything over ~ 0.060" irrelevant).... The last .30 cal trial used a 27 gram hammer instead of the 51 gram.... SSG guide assembly (spring and guide) weigh 22 grams.... Hammer stroke = 0.79" (at zero gap)....
Initial .25 cal. tests.... (0.60" preload, 0.0344" jet, 51 gram hammer)....
.25 cal. 25.4 gr. @ 1900 psi... plateau velocity = 1096 fps @ 2 turns gap or less
4 turns gap = 1085 fps
6 turns gap = 1068 fps
7 turns gap = 1058 fps
8 turns gap = 1042 fps
9 turns gap = 1020 fps
10 turns gap = 380 fps
.25 cal. 34.1 gr. @ 1900 psi.... plateau velocity = 999 fps @ 2 turns gap or less
4 turns gap = 982 fps @ 0.71 FPE/CI
6 turns gap = 965 fps @ 0.92 FPE/CI
7 turns gap = 954 fps @ 1.01 FPE/CI
8 turns gap = 940 fps @ 1.11 FPE/CI
9 turns gap = 887 fps @ 1.42 FPE/CI
10 turns gap = 335 fps
.25 cal. 52.7 gr. @ 3000 psi.... plateau velocity = 992 fps @ zero gap
2 turns gap = 979 fps
4 turns gap = 959 fps
5 turns gap = 942 fps
6 turns gap = 920 fps
7 turns gap = 826 fps
8 turns gap = 420 fps
Additional .25 cal. test with 0.40" preload @ 1900 psi using 34.1 gr.... plateau velocity = 989 fps @ 2 turns or less gap....
4 turns gap = 980 fps
6 turns gap = 963 fps
7 turns gap = 949 fps
8 turns gap = 900 fps
9 turns gap = 470 fps
Initial .30 cal. tests.... (0.60" preload, 0.0344" jet, 51 gram hammer)....
.30 cal. 44.9 gr. @ 1900 psi.... plateau velocity = 980 fps @ 2 turns gap or less....
4 turns gap = 971 fps
6 turns gap = 958 fps
7 turns gap = 945 fps
8 turns gap = 910 fps
9 turns gap = 860 fps
10 turns gap = 300 fps
.30 cal. 49.7 gr @ 1900 psi.... plateau velocity = 960 fps @ zero gap....
2 turns gap = 948 fps @ 0.92 FPE/CI
4 turns gap = 940 fps @ 0.95 FPE/CI
6 turns gap = 922 fps @ 1.04 FPE/CI
7 turns gap = 902 fps @ 1.11 FPE/CI
8 turns gap = 870 fps @ 1.29 FPE/CI
9 turns gap = 803 fps @ 1.39 FPE/CI
10 turns gap = 270 fps
.30 cal. 49.7 gr. @ 3000 psi.... plateau velocity = 1093 fps @ zero gap
2 turns gap = 1080 fps
4 turns gap = 1062 fps
6 turns gap = 1045 fps
7 turns gap = 1012 fps
8 turns gap = 390 fps
.30 cal. 67.2 gr. @ 3000 psi.... plateau velocity = 980 fps @ zero gap
2 turns gap = 970 fps
3 turns gap = 958 fps
4 turns gap = 933 fps
5 turns gap = 895 fps
6 turns gap = 850 fps
7 turns gap = 770 fps
8 turns gap = 480 fps
Additional .30 cal. data point.... 109 gr. @ 3000 psi.... 811 fps (159 FPE) with 1 turn preload (-1T gap)....
Jet removed for remainder of .30 cal testing.... Preload 0.40" (3.2 lbs).... 34.1 gr. @ 1900 psi....
With original 51 gram hammer.... plateau velocity = 960 fps @ 2 turns gap or less....
4 turns gap = 957 fps
6 turns gap = 940 fps
7 turns gap = 925 fps
8 turns gap = 896 fps
9 turns gap = 330 fps
With above, and lighter 27 gram hammer.... plateau velocity = 950 fps @ 1 turn gap or less....
2 turns gap = 945 fps
3 turns gap = 935 fps
4 turns gap = 917 fps
5 turns gap = 870 fps
6 turns gap = 670 fps (unstable, ES >100 fps)
7 turns gap = 225 fps
Efficiency testing was done by shooting 1 mag. (8 shots in .25 cal or 7 shots in .30 cal) tethered to a 500 cc bottle with 1900 psi regulated output and measuring the pressure drop in the bottle for that 1 mag. with a good gauge.... That is essentially all the testing I have done to date.... Have fun !!!
Bob
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Man you were a busy Bee today!!! Glad its winter its the only time we get to see you posting Data. Bob do you have a .025 jet or just use a 4mm bolt and drill it. I think youll be surprised at what youll see. Or maybe not you have you look like you have a firm grip on it.
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Nope, only the one #87.5 jet (which I think is 0.034" ? ).... The only drills I have smaller than a #60 (0.040") are 1/32" (0.031") and 1/64" (0.016").... Nice to know that the threads a M4 though, thanks for that tidbit....
I guess the 6-32 SHCS jets I made for my homemade SS valve for the 6mm / .257 project are a bit too large.... They start at 3/64" (0.047") and go to 3/32" (0.094").... ::)
Bob
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Nice looking test data you have gathered there Bob, you guys are having fun while I'm up to my neck in physics study and material technology.
At least later is interesting.
Does the valve act similar to Cothrans, where if you tap the valve just enough to open it it blows wide open?
Keep up the good work, it is interesting to follow.
Marko
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...Does the valve act similar to Cothrans, where if you tap the valve just enough to open it it blows wide open?
Keep up the good work, it is interesting to follow.
Marko
Two takes on the same idea- a balanced valve. Yes, light strike= big power. Although, the SS valve allows an even lighter strike and more adjustability, or tunability rather. The Cothran valve is adjusted via pressure. The SS valve allows for more tunability via pressure and hammer strike. Or that's my grasp of the situation. Please correct me if I'm wrong guys.
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Thanks for taking the time to post all the data (seriously - wow). I may get a few things incorrect but I am trying. It is so much information and I am putting things together that are apples to apples testing ( I think ).
For the 25 I can only do SSG setting vs valve to have an output for FPS/FPE. If we had the efficiency numbers for both runs of the 34 grains at .4"/.6" preload at 1900psi I could have added that data in to see what the most efficient SSG set up would be for a given fps/fpe.
A little bit about the graphs first. A line that is close to or near horizontal typically means that adjustment does not influence major changes in the output. Although lines that are more vertical have a major impact in the output.
The interactions plots are used to do just that, and are fixed. They just show what things are doing. Although, the optimization plot is dynamic. Adjustments can be made to the factors (with in the range of the design) to predict the output (or in other words - optimize it).
So I wanted to put the SSG information into tables first to get an understanding of gap,preload, and cocking effort. In the DOE, I used just SSG setting but, it can be changed to cocking effort,gap, or preload for a better understand of energy needed to crack the valve.
Here's the SSG table
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Main effects and interactions plot was kind of interesting. The interesting part for me was the interactions plot. It indicates that a high SSG preload is more stable within a desired fps/fpe range. Although, less SSG preload has more of a broad range of FPS/FPE but does not seem to be as stable. This may have to do with the free flight of the hammer at different distances ( I don't know ).
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I wish to add this to the conversation. You guys do all the heavy lifting and every AG addict on the planet benefits either directly or indirectly form all the research and hard work.
Thank you all from one of the direct beneficiaries. The .30 Marauder that Lloyd built for me with the custom TJ's barrel , Cothran balanced valve and I believe Huma Regulator it is a great proof of what you guys are accomplishing through research and collaboration.
So again thank you all
Regards,
Don AKA Sfttailrdr46
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The best thing I like about Factorial design is that we can use the optimization plot dynamically and (guess) what should happen at any setting with in the scope of the design.
For example. If you wanted to set your gun up for a given "cocking effort" with a known gap that provides the best efficiency and shot to shot consistency, you just have to change the factors (settings) and you can see what the result "should be" without even shooting the gun.
It comes pretty close but I am off around 10 fps right now to the raw data. That's not as important as what the information is telling you though (IMO).
So I did three optimization plots trying to maintain 950 fps and trying to keep the gap a small as possible. Here's what it looks like.
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Sorry I can't do the 30 with jet sizing. Missing 2 data points and don't want to guess. I guess this is a good start to understanding the valve a little more for me. Thanks again for all the data Bob. Great work
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Man, the wealth of knowledge astounds me! Amazing work guys!
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Whats really neat is, Bob did the initial screen test for the limits (max/min). If we were to do the DOE now (design before shoot), you can actually dial it in more accurately.
Whats even neater too me is just by doing 4 to 6 test shots with different settings can and will give you every possible setting of preload,gap,SSG turns, and jet size for a desired output such as efficiency,fps/fpe, and max cocking effort with the couple clicks of the computer instead of shooting gobs of pellets and using lots of air.
Testing goes from a couple days to a couple hours.
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Marko, I don't think the Cothran "blows open" exactly.... because if that were the case you could not reduce the air usage by using less hammer strike, or limiting the distance the hammer can drive the stem with an O-ring or energy absorbing bumper on the back of the valve.... It definitely has a "cycle" to it, however, whereas the ART/SS valve seems to act more "normally" in that you can adjust the velocity somewhat by changing the hammer strike.... Conventional valves will also reach the point where they only "pop" and deliver minimal velocity, but they arrive there much more gradually....
One thing I have noticed with both the Cothran and ART/S valves is that heavier pellets seem to increase the dwell, or rather light ones (or no pellet) decrease it.... When you get close to the cliff with either valve, if you shoot without a pellet, the valve just pops, hardly releasing any air.... This doesn't happen when the valve is opening lots (or at least you don't know it).... just when it is barely cycling properly.... which is of course when it is the most efficient as well.... This quicker cycling when dry fired (or using a light pellet) most likely is a result of the rapid decline in pressure on the downstream side of the poppet, which being barely open is then slammed shut by the pressure inside the valve.... The heavier the pellet, the longer the pressure difference across the poppet head is minimized....
I wish it was that easy, Tim, but perhaps your predictions will make it so.... IMO, the non-linearity of the preload/gap vs. velocity curves makes interpolation using 2 or 3 points inaccurate, if not downright misleading.... As an example, how would you deal with a Cothran valve, where there is no velocity change over many turns of gap adjustment, and then it basically quits working suddenly over just 1 turn more gap?....
BTW, the hammer stroke is 0.79", not 0.68" as you used in your data.... not sure where you got 0.68".... In addition, when I say "zero" gap, I actually have a very slight gap (something on the order of 1/6 turn) to make SURE that there is no preload on the spring, and zero chance that the SSG can add any closing force to the valve.... so you might be well advised to add 0.010" to all the gaps.... ie "zero" is actually about 0.010" gap, 2 turns is 0.121", etc.... Good Luck !!!
Bob
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Thanks Bob,
I was comparing the cothran and art valve to fury valve, and there I have a point where the valve will cycle fully open or just a little pop. It blows open when opened past some point. That margin is Very narrow, just as simple as hammer cocking lever rubbing slightly against the frame and it did pop and nothing more. One 2mm shim sorted that problem.
I know how the Travis has built the valve, and how Cothrans valve is made, my valve is alot similar to that, minus some parts and something modified.
The ability to tune the art valve for smaler bore guns is very good, and I can see why.
I would say for all around valve the adaptability of The Art valve is the best in the market, it suites small and medium bore guns.
I'm interested how well it will scale up to the big bores...
Keep up the good work guys!
Marko
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Marko it works well with any bore size you just have to scale up the piston diameters. It almost doubled the FPE of the Bulldog 357 and increased shot count by a good margin when tuned back to stock power levels. Give it a go Marko when your caught up with schooling your one of a few who have actual knowledge of the internal workings.
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Travis, as soon as I'll have the Emco Cnc turn up and running, still waiting for the darn chuck to be delivered.
I will give it a go, and you will be the first to know.
Too little time to be standing at the lathe turning, so the cnc will definitely help with my testing different designs.
Its the little parts that take most of the time to turn, taking small cuts with a manual lathe is very time consuming, right Bob?
Spring period will be more easier for me, for I have experience on most of the courses and dont need to attend as much. Mostly material and manufacturing technology, 10 years as a machinists and welder gives me a slight edge over the youngsters. ;)
Marko
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Tim, here are five more data points for you.... I extended the striker 1/8" on the 27 gram hammer, so the hammer stroke (no gap) is now 0.66".... This data is for the .30 cal, with 49.7 gr. pellets, at 1900 psi.... The zero gap starting point is, of course, 1/8" further out.... Also, spring preload has been reduced to 0.35" (~2.8 lbs.)....
Zero gap = 950 fps
1 turn gap = 935 fps
2 turns gap = 890 fps
3 turns gap = 820 fps
4 turns gap = ~ 300
Looks like the shorter hammer travel (and slightly reduced preload) moved the cliff another couple of turns closer to zero gap.... I would not move it any further, so this setup looks about optimum to achieve the desired tuning range without having too much gap....
It is important for everyone to realize that my ART/SS valve is NOT stock, it has a 1/4" exhaust port instead of 3/16" and currently is running no jet in the inlet (ie wide open).... I am interested in power over efficiency at the moment....
Bob
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Bob, thats great you have a striker on there. With the such low cracking force of the valve and using a shorter stroke looks like it should be advantageous in couple ways.
Reducing the preload as you mentioned.
Less cocking effort.
Moving the cliff to allow for more adjustability ( fine small adjustments will make big swings )
Possibly helping with the valve running away when fired below regulated set point.
Faster lock time with such low hammer spring.
Even though you are doing this all with the hammer and spring power plant, I have a feeling that the jet helps tunes this out smoother for a more manageable adjustment through out the hammer spring setting and hammer weight.
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I like preload (with a gap), it is part of the SSG concept, and reduces cocking effort compared to equal hammer energy with an SSS (and I would not use a conventional preloaded spring with this valve).... Actually reducing the stroke would require more preload, or less gap, of course.... Cocking effort is already a joke, you certainly don't need to reduce it further.... I have requested Travis send me a stock MRod spring to try, that will be PLENTY, pretty good when you are talking a 90-100 FPE in .30 cal.... The valve now has ease of adjustment, one turn of gap changes the velocity between 15 - 70 fps.... and you can easily make 1/12 turn adjustments visually with a hex head on the gap adjusting bolt.... put a mark on one point of the hex, and think hours on a clock.... The lock time is already VERY low because of the 27 gram hammer....
As far as the valve "running away", I haven't seen that even with lots of preload.... which is the same as running lower pressure than the tune is for.... Yeah, it uses a ton of air, but that is because the preload is resisting the low closing forces on the valve.... I have NEVER seen any tendency towards valve bounce, or "machine-gunning" at any setting, and certainly not with a gap in the SSG....
I don't have enough experience with changing the jet (two data points, small and way too big).... However, from that small amount of data, and talking to Travis, it seems that a smaller jet gives you a wider velocity adjustment range between the plateau and the cliff.... My worst case was only 60 fps (low preload, no jet).... most run about 100-120 fps, with heavy bullets running closer to 150 fps.... Compare those to a Cothran where if you dial it down only about 40-50 fps, at which point you get a huge ES, and then the cliff.... Travis says that in smaller calibers, with smaller jets, you can get about a 300 fps adjustment range....
Why would you ever need more?....
Bob
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A good example of wanting more would be your 25.39 testing vs 34 grain shooting at 1900 psi (25 cal). You can not have both of the best speeds for accuracy without changing anything else except a hammer spring adjustment.
I am learning as much as I can from your testing in the hopes that someone does not have to put all that money and time into additional parts to allow the valve to work more traditionally with such a low cocking effort ( a nice happy medium ).
Not too many people do what we do and may get disappointed if they just dropped this valve in their gun with no other "part" changes.
The runaway part is important to understand (too me) because I am now running un-regulated. I also run tunes from 1500psi down to 1000psi goofing around with 50 fpe tunes. But, then I like to charge to 3000 psi and shoot down to 2300 psi for 80 fpe tunes. I hate taking the gun apart and I am sure other people do too, so all I have to do is adjust my hammer spring adjuster.
The comment amount the smaller port makes sense (smaller more range) but, I have a feeling it also changes the cracking force which in turn allows for different hammer and hammer spring changes making act more similar to a conventional valve. I could be wrong though and the port does other stuff like changes dwell. I have no idea.
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OK, I understand.... you want to be able to change ammo and shoot both in the 900s with only a hammer spring preload change.... On a regulator, you can do that with a conventional valve, with a Cothran it is out of the question.... I don't know about a stock ART/SS, because I never tried that.... When I develop a gun, I have an idea what I want, and once tuned I never change either ammo or velocity.... So far, though, I haven't seen anybody "disappointed" with the new valve.... ::)
If you are running unregulated, as long as you have enough power to shoot the 34 gr. at 70 FPE within allowable fill pressure.... then you can easily shoot the 25 gr. at 50 FPE (or less).... by just dropping the fill pressure.... You may not even have to alter the preload/gap....
If you have an externally adjustable regulator (yes, they are around).... then you can do whatever you want, from basement plinking to max. power.... with any suitable weight ammo of course.... Lots of ways to skin a cat.... 8)
Bob
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A good example of wanting more would be your 25.39 testing vs 34 grain shooting at 1900 psi (25 cal). You can not have both of the best speeds for accuracy without changing anything else except a hammer spring adjustment.
I am learning as much as I can from your testing in the hopes that someone does not have to put all that money and time into additional parts to allow the valve to work more traditionally with such a low cocking effort ( a nice happy medium ).
Not too many people do what we do and may get disappointed if they just dropped this valve in their gun with no other "part" changes.
The runaway part is important to understand (too me) because I am now running un-regulated. I also run tunes from 1500psi down to 1000psi goofing around with 50 fpe tunes. But, then I like to charge to 3000 psi and shoot down to 2300 psi for 80 fpe tunes. I hate taking the gun apart and I am sure other people do too, so all I have to do is adjust my hammer spring adjuster.
The comment amount the smaller port makes sense (smaller more range) but, I have a feeling it also changes the cracking force which in turn allows for different hammer and hammer spring changes making act more similar to a conventional valve. I could be wrong though and the port does other stuff like changes dwell. I have no idea.
You need to work with a balanced valve at least once Tim your understanding of the parameters is limited and making assumptions based on no actual data of your own makes you look like your trying to force certain parameters of a conventional valve to work with completely different technology. But for 30 cents you can make a SS valve work just like a conventional valve.
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Yup. Your probably right Travis but, I am learning so much from Bob about how to and not how to use a "balanced valve" properly. Knowing that the SS valve can be used as a conventional valve too is a plus. Is it just closing off the jet ?
Have been trying to wrap my head around the cliff and the adjustability through the plateau (on/off opening).
Been running spring calculations this morning to try and get a better understanding. It would appear, that using a balanced valve, it is nearly imperative to run a SSG due to how the SSG set up with a preload leans out the spring rate curve. And, by using any kind of SSS would be extremely touchy. An SSS would have a very narrow plateau and can over power the balanced valve (creating that run-away).
I wouldnt have believed it until I put the tables together and charted them. I am super interested now about the comment that the cothran valve is slighter harder to open and has a shorter plateau than the SS valve but had a higher efficiency. I had to go back to the beginning of this post to see what SSG was used. Big difference from a 12Lb spring to 8 Lb spring.
It would be interesting to see how the cothran valve would fair with the identical SSG set up/hammer weight as the SS valve. I am not asking to do that because you have done so much already but, it sure would be interesting.
Going to the 6lb/in spring with a 3.2lb preload looks like it will be the ticket to extending the plateau, being able to use only .015"/.02" gap would be nearly full open on the valve.
I hope I am learning something here. Thanks for sharing all the information (and putting up with dumb questions and comments). ;D
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I tested the Cothran valve in the BRod using the SAME setup as the ART/SS valve, same spring, same preload and it was harder to open.... You must have missed that.... Reply #233.... The cliff occurred at about 3 turns less gap with the Cothran....
Bob
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Yeah I missed that. I thought during that time the jet size in the SS valve was .0344" and not the later tuning with .06"/.125 wide open. I was looking at the last round of testing when you removed the jet on the SS valve to allow it to open easier and have a shorter plateau.
"Jet removed for remainder of .30 cal testing.... Preload 0.40" (3.2 lbs).... 34.1 gr. @ 1900 psi....
With original 51 gram hammer.... plateau velocity = 960 fps @ 2 turns gap or less....
4 turns gap = 957 fps
6 turns gap = 940 fps
7 turns gap = 925 fps
8 turns gap = 896 fps
9 turns gap = 330 fps"
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Your table above is still done using 0.68" of hammer travel, which is incorrect.... so you can't rely on that table and chart as I said before.... The hammer travel was 0.79" for everything except the last run with the 27 gram hammer with the striker adjusted out 1/8", where the travel is 0.66".... In addition, the yellow highlighted cells in your table for the two preload condition on the 8 lb/in valve are both at the same gap (4 turns).... The proper comparison would be to use 1 turn less gap for the 0.040" preload, comparing them at the same gap is meaningless....
Here is the raw data for the Cothran valve.... .30 cal. 49.7 gr. @ 1900 psi.... 0.40" preload, 8 lb/in spring, 51 gr. hammer and 0.79" hammer travel....
Zero gap = 953 fps
1 turn gap = 950 fps
2 turns gap = 947 fps
3 turns gap = 907 fps (ES > 50 fps)
4 turns gap = 372 fps
Reducing the preload on the SSG from 0.60" to 0.40" moves the cliff 1 turn, so for a direct comparison with the SS valve, at most the cliff on the above Cothran run would be at 5 turns gap with 0.60" of preload.... That compares to the cliff being at about 9 turns out for the SS valve with the same configuration.... In addition, the Cothran has virtually no USABLE velocity adjustment range, it has a plateau and a cliff.... The 907 fps at 3 turns of gap (above) with the Cothran came with a ES of over 50 fps.... Also, I didn't "remove the jet to make it open easier and have a shorter plateau", I simply did it to see what effect that would have.... It actually didn't change the position of the cliff, it made less of a "knee", reducing the velocity adjustment range available.... The valve acted a bit more like the Cothran valve when I removed the jet (although maintained some adjustability).... It didn't increase the maximum power, although it extended the plateau to greater gap, and in fact I can't really see any "advantage" to removing it (which is just what Travis said, surprise-surprise).... He maintains that using an even smaller jet will allow an increase in the velocity adjustment range....
I see no reason you could not use an SSS with the ART/SS valve, but "Stiff" will take on a completely different meaning, as it might mean a 10 lb/in spring instead of a 6 lb/in spring using an SSG.... The problem I could see that using an SSS with a spring that soft may allow it to absorb energy on the rebound and bounce, but only trying it would tell you.... The alternative, if you insist on using a very stiff spring, would be to drastically shorten up the hammer stroke, so that the SSS isn't compressed very far when cocked.... I would think that would make it extremely sensitive to adjust....
You keep referring to the valve "running away" when the pressure is drastically below the tuning point (eg. below regulator setpoint).... and I have repeatedly asked you to clarify, but you just keep insisting that is a problem.... I don't get it ??? .... You haven't used an ART/SS valve, so what are you basing that comment on?....
Bob
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The run away started with Dairyboy with a complete dump around 2000psi. The second was with PCPshak (sorry if that the wrong name but it's what I remember). The last one was with Motorhead making the comment that his ran away too.
In PCPshak's case (sorry for the name again), his was extremely dangerous as it extruded his shroud and locked his LDC on to it.
Now these guys are not knuckle heads and know how to tune.
So yes, I am concerned that if I buy a valve and don't know enough about it that I will either damage or hurt myself or someone else. Just wanted to fully understand what I would be getting into if I bought a SS valve.
I can see that your getting aggravated so, I will show myself to the door and avoid conflict. I thought I could use some of your information and ask questions since there is nothing out there in regards to what happens if you do this or that with the valve and your information has been more than anything since and before the valve has been launched.
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The run away started with Dairyboy with a complete dump around 2000psi. The second was with PCPshak (sorry if that the wrong name but it's what I remember). The last one was with Motorhead making the comment that his ran away too.
In PCPshak's case (sorry for the name again), his was extremely dangerous as it extruded his shroud and locked his LDC on to it.
Now these guys are not knuckle heads and know how to tune.
So yes, I am concerned that if I buy a valve and don't know enough about it that I will either damage or hurt myself or someone else. Just wanted to fully understand what I would be getting into if I bought a SS valve.
I can see that your getting aggravated so, I will show myself to the door and avoid conflict. I thought I could use some of your information and ask questions since there is nothing out there in regards to what happens if you do this or that with the valve and your information has been more than anything since and before the valve has been launched.
Thats why I updated the thimble and poppet Its now impossible for that to happen Tim but you didnt mention that did you and I posted that and Im sure you read it! Your Help as you call it is nothing more than your attempt to discredit my valve. What ever Tim and Ill go back to playing with my SS valve you can go back to working on my valve design you took credit for(that I abandoned) I feel no need or want to cock 20+ pound springs anymore thats as dead to me as riding a Big Wheel over driving my car. You were not fulling me with your spring chart and Help as you call it. Your very transparent I knew your motives from your first post. You know what else is dangerous Tim Hanging a 24lb spring on the very fragile marauder sear and selling it to the public.
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I do see Tim trying to question the new SS valve with a negative undertone over a number of post. I know Tim is even toying with his own valve at a price that will undercut the SS valves price and hints at this in his valve thread. I am not naive and can read between the lines.
I like all parties involved and like to stay neutral until I see this kind of thing going on. I have all confidence in the SS valve and would say different if the need arises. I have never had a dump situation with mine and feel like if there were a problem with the SS
valve, I would've seen one by now myself. Travis has admitted to some issues with the SS valve and has stated clearly that he is aware of them and is working overtime to correct them and make things right with all of his customers. I can't think of anything else one could ask for.
I am currently running my Cobra valve because I messed with the SS valve and now can't get it to seal completely. The cocking is ridiculously hard on the Cobra using Tim's dual dimensional spring. I can't wait to get my SS valve fixed and get back to easy stock like cocking with the SS valve.
I hope Tim actually does try to develop his valve and then he will get a good taste of what it really takes to do that and be successful with the ever present naysayers who have no clue themselves making comments.
I hope Tim takes my strong comments towards him as useful, but if not I'll have learned more about him.
If Tim wants to compete with his own valve I am all for it, but let's be respectful of others efforts to enhance our hobby in doing so.
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Today I assembled the regulated tank block I got from Travis back in the summer.... It went well, and after a short learning curve installing shims, I was able to adjust it from 1000 psi up to over 2000.... I didn't try and go higher, but I am sure it will.... It has a 3K burst disc on the output side, and I didn't want to push it.... The adjustment is quite sensitive, you don't have to turn the 10-32 adjusting setscrew very far to move the output by 100 psi.... maybe 1 flat on the allen key or less....
Since the Cothran valve cannot be adjusted using hammer preload (or SSG gap), and needs to have the pressure adjusted to change the velocity, or retune for a different pellet weight.... it was a perfect match for an externally adjustable regulator.... Since there are two excellent pellets made by JSB that are quite different in weight (25.4 gr. and 34.1 gr.) I decided that to install the .25 cal upper on the lower that used the Cothran valve and the adjustable regulated tank block and I installed a 500 cc, 3000 psi bottle on it.... My initial adjustment of 2000 psi drove the 34.1 gr. JSB King Heavies at over 980 fps, but I used the opportunity to find out where the cliff was, and where the SSG gap needed to be adjusted to be close to the cliff, but solidly on the plateau, where the valve is operating stably.... That was with 2 turns of gap.... Then I shot the tank down to about 1700 psi so that I could drop the setpoint adjustment....
When increasing the setpoint pressure, you back out the 10-32 screw, which lowers the HP seat, moving it away from the piston and Belleville stack.... The seat opens, allowing more air to flow to the output side, raising the pressure and pushing the piston towards the (now lower) seat, against the Bellevilles, compressing them until the seat closes at the now higher pressure.... This puts no additional load on the seat, and can be done at any time.... When you want to decrease the output pressure, however, you need to drop the tank pressure below not only your current setpoint, but also below where you want the new setpoint to be.... The reduced pressure on the piston allows it to move away from the seat, and this allows you to turn the 10-32 screw in without putting additional pressure on the seat and possibly damaging it.... I wanted to start at 1800 psi and work my way back up, so I drained the tank down to 1700 and turned the 10-32 adjuster in until I felt slight additional resistance when the seat contacted the piston.... If you do this carefully and slowly, you can feel when they make contact.... When I added more air to the bottle, the gauge on the output side of the tank block moved up slightly, to about 1800 psi.... I shot a few shots, and the velocity was down to about 920 fps, so I simply backed the 10-32 adjusting screw out a fraction at a time, shooting a couple of shots at each setting, until I got my target velocity of 950 fps.... I then shot a couple of shots at each SSG gap setting, and recorded the results, which are on the graph below in red....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Cothran%20Regulated_zpsled0azhx.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Cothran%20Regulated_zpsled0azhx.jpg.html)
You can see the typical "cliff" exhibited by the Cothran valve which starts just before 3 turns out.... The velocity at 3 turns out is very unstable, with an ES of nearly 200 fps, because the valve is about to fall over the cliff.... However, at 2 turns of gap, it is rock solid, with about a 1% ES.... From previous experience I know that is the optimum place to run a Cothran valve, with the lowest hammer strike that allows stable operation and low ES.... I tried the 25.4 gr. pellets, and the velocity was over 1050 fps, so to get them to work I knew I had to lower the setpoint pressure.... I started simply shooting the 25.4 gr. pellets and watched the velocity fall as the pressure dropped.... I was pretty shocked to discover that to get down to 950 fps I had to drop the pressure in the tank all the way down to 1400 psi.... I shot a few more shots, to drop the tank pressure to 1300, and then turned in the 10-32 adjusting screw until I could feel it contact the seat.... I added air to the tank, the output gauge barely budged, and the velocity settled in at about 910 fps at about 1300 psi.... I slowly backed out the pressure adjusting screw, shooting a couple of shot at each adjustment, and stopped when the velocity with the 25.4 gr pellet reached my target of 950 fps.... The gauge indicated 1400 psi.... and I confirmed that by shooting the tank down until the velocity just started to drop, while the tank was still connected to the accurate gauge on my Great White.... Yes, I was getting 51 FPE at only 1400 psi.... I ran through the gap adjustments, and recorded the other curve (in blue) on the graph above.... The optimum gap was at 3 turns out, and the cliff started at 4 turns out, 1 turn more than at 1900 psi.... As expected, the valve requires a bit less hammer strike at 1400 psi than at 1900.... I also shot a few of the 34.1 gr Heavy pellets at that same setting, and that velocity is shown on the graph above as the black dot (872 fps).... So, with the 34.1 gr. pellets, I was getting 57.6 FPE at only 1400 psi.... pretty remarkable, and no adjustment made from the 950 fps setting with the 25.4 gr Kings....
Now that I knew that 3 turns out was the optimum setting for the 25.4 gr. Kings at 1400 psi, I recorded the pressure in the 500 cc bottle (using the gauge on my Great White), and shot 8 shots, on regulator, at 1400 psi.... I averaged the velocity (952 fps = 51.1 FPE), and recorded the pressure drop, which was 200 psi.... That works out to 0.97 FPE/CI, which is pretty low, but we are in new territory here, getting 51 FPE at only 1400 psi.... I repeated the test using the 34.1 gr. Heavies, and as I expected, the pressure drop was exactly the same, at 200 psi.... Since the energy per shot increased to 57.6 FPE, however, the efficiency increased to 1.10 FPE/CI.... I then backed out the 10-32 pressure adjuster to increase the setpoint back to 1900, set the SSG gap at 2 turns, and shot another 8-shot magazine at that setting with the 34.1 gr. Heavies.... The pressure drop was just over 200 psi, so I recorded it as 210 psi, and with the average velocity of 950 fps (68.4 FPE), that works out to an efficiency of 1.24 FPE/CI.... pretty decent at that power level....
The pressure drop per shot for all these tunes runs just about 25-26 psi per shot from the 500 cc bottle.... If we use a fill pressure of 3000 psi, with the 1900 psi setpoint, that should give 42 shots at over 68 FPE with the 34.1 gr Heavies.... and with the 1400 psi setpoint, that should give 64 shots at 51 FPE with the 25.4 gr. Kings and nearly 58 FPE with the Heavies.... I think those are quite acceptable numbers, and tuning back and forth between the 25.4 gr. and 34.1 gr. pellets (both at 950 fps) requires only resetting the external regulator adjustment, and one turn on the SSG gap.... In fact, if you don't care about getting the full 64 shots at the 1400 psi setting, you don't even have to change the SSG gap, you can leave it at 2 turns, and just lose a few shots.... If you have the gun tuned at 1400 psi, you can shoot the Kings at 950 fps and the Heavies at 870 fps, for the same number of shots, with NO adjustment necessary....
Bob
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Most impressive Bob!!
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I neet to get you some smaller jets to finish up the testing
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Today I worked on a new SSG to go inside the AR style stock adapter I made a while back.... I had to shorten up the adjusting bolt and spring guide so that it wouldn't interfere with the stub on the stock, as this is a paintball stock and uses a plastic slider.... This version uses a PRod trigger with a taller sear from Lloyd at AirGunLab to work with the thicker MRod tube.... The forestock is a simple piece of ABS plastic pipe slide over the main tube and secured with setscrews.... Here is what the finished gun looks like....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20BRod%20AR%20Cothran%20Valve%20and%20Adjustable%20Regulator_zpsr0uhj1mh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20BRod%20AR%20Cothran%20Valve%20and%20Adjustable%20Regulator_zpsr0uhj1mh.jpg.html)
The 500 cc tank is heavy, so the all up weight is 9.5 lbs including the scope and rings, so the bare gun is about 8 lbs.... If you hold it with your hand just behind the tank block, it balances right there.... It uses the Cothan valve and the Cobra tank block with externally adjustable regulator.... It is currently tuned to shoot the 34.1 gr. JSB King Heavy MkIIs at about 950 fps (68 FPE), for about 40 shots per fill.... With the Cothran valve, the easiest way to adjust the velocity is with the regulator.... the pressure adjustment (currently 1900 psi) is a 10-32 setscrew on the bottom of the tank block.... The barrel is a LW Polygonal, 23.8" long, and fitted with a Hatsan Air Stripper.... The MROd receiver was bored out about 1.5" to accept the larger diameter barrel.... so the free floated barrel is very rigidly mounted to the receiver.... The bolt was fitted with a 3/32" diameter probe, making the chamber area the same as the barrel and transfer porting, which is 0.234"....
All in all, I am very pleased with the way this turned out.... It is easy to cock, with the SSG having 3 lbs. of preload on an 8 lb/in spring.... The 51 gram MDS (steel cored) hammer has 0.79" of stroke, and the SSG gap at this tune is 2 turns, so the cocking distance against the spring is 0.67", making the maximum cocking force less than 8.5 lbs.... About the only thing that would be a nice addition is a BiPod mount on the bottom of the tank block.... My thanks to Travis and Lloyd for their help in procuring the parts for this build, without them it would not have been possible....
Bob
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That looks FANTASTIC and really the only upgrade would be the Acecare 500cc 4500psi carbon tank other than that its really about as good as it gets. Its a performer also!!! Not just a closet queen. Now its time to hit the field with it!!
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Yes, that would take about 1/2 lb. off the weight, and more than double the shot count.... All that would be needed to use it would be to swap out the 5/8"-18 NF tank adapter for one with 18 mm x 1.5 mm threads (which I have).... The gun is protected by a 3K burst disc, so no danger even if the regulator bypasses....
Bob
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Nice clean lines, and good shot count too.
Marko
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Today I took apart the other lower, with the ART/SS valve in it, and cleaned it up and reinstalled the #87.5 jet that it came with.... After a couple of experimental settings of the hammer stroke and SSG preload and gap, I ended up using the 27 gram hammer with the striker set flush with the front face.... I lowered the preload to 0.37" (just 3 lbs.) and I was running low on my supply of 50 gr. JSBs, but I had a tin of the 45 gr. FX (JSB) pellets, so I used those to collect the data of velocity vs. preload, with the following results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20New_zpsol3rxmcb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20New_zpsol3rxmcb.jpg.html)
The combination of the stock jet and the very light hammer gave me a much nicer curve, with a full 200 fps of velocity adjustment before the valve fell off the cliff.... This is the widest range I have seen with the SS valve.... Once again, as soon as there was negative gap (preload) on the SSG, the gun became an instant air hog, and barked and kicked like a big angry dog.... However, as soon as there was any gap at all, the report was sharp and crisp, and just gradually became quieter as the velocity dropped, exactly like a conventional valve would do.... I set the SSG gap at 2 turns (just under 1/8") and tethered the gun to my 500 cc bottle with the output regulated at 1900 psi (actually just under).... I left the bottle tethered to the gauge of my Great White (tank valve closed), so that I could check the pressure drop to measure the efficiency.... I did two 7-shot mags. and got an average of 940 fps (88.3 FPE) with about a 1% ES, and the pressure dropped 250 psi for each mag., which works out to an efficiency of 1.18 FPE/CI.... Without changing any settings on the gun, I tried a 7-shot mag. with the 50.2 gr. JSBs I had remaining, and recorded an average velocity of 886 fps (87.5 FPE), but the pressure dropped only 200 psi.... Very surprised by that, I repeated the test, with exactly the same results.... That works out to 1.46 FPE/CI, which is pretty incredible for a .30 cal at that power level....
There is something different going on with this valve, that may be the key to some of the high efficiency numbers we are seeing.... I don't know if it has to do with the reduced velocity, or the slower pressure decay that causes in the valve throat.... but I have never seen such a drastic increase in efficiency before with only a 10% increase in pellet weight.... Normally you would expect the valve to release slightly less air with the heavier pellet, because it "uncovers" a shorter barrel length during the valve dwell, which essentially stays the same, and that results in a slight increase in efficiency.... For some reason, with the heavier pellet, this valve used less air.... a LOT less air, a drop of only 200 psi with the 50 gr. pellet compared to 250 psi with the 45 gr.... I am at a loss to explain why.... Perhaps the higher the pressure in the exhaust port the faster the valve closes, increasing the efficiency.... I don't know, but I like it.... 8)
I would like to increase the velocity with these two pellets a bit, so I think I will add a thin shim to the regulator to bump the setpoint a bit.... I would like to be able to adjust the velocity of the 50 gr. between 900-940 fps and the 45 gr. between 940-970 fps just by changing the SSG gap, and not have too big a gap (or too small).... I wish I had another Cobra tank block, with the externally adjustable regulator, but it is more important for that to be paired with the Cothran valve, which has no velocity adjustment expect by pressure.... At least I will have no worries about getting enough hammer strike with this valve.... the gun is very easy to cock, and I have lots of preload adjustment available, with only being at 3 lbs. at the moment....
My biggest problem now, is that I have been burning through pellets like crazy.... and so much air I had to rebuild my ShoeBox a couple of days ago (I got 90 hours on the HP O-rings in my Freedom 8, not bad).... Still, doing lots of shooting and collecting lots of valuable data is worth spending a few bucks, right?.... I hope my wife agrees.... ::)
Bob
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I know I said this before but running a slightly smaller jet will close the valve faster for those lighter pellets and give you the same reaction as lowering the spring pre-load. More pellets/more air/ more time. Answers dont come cheap Im well aware of that. The Brod updates are my favorite thing on GTA right now no matter what valve etc. you use. Tons of useful data. The magic happens when the Jet and spring load are in harmony. One more thing Im probably going to tick off a few customers but with this light of a valve energy needed Im looking back at a internal SSG with light hammer for the Mrods. No cocking energy problem so now the SSG really shines again in a small space....aaaarrrgghhhh
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I agree, Travis.... I think an SSG based on the stock MRod spring, with only about 3 lbs. of preload (on the guide) would be great.... at least to start, for most tunes.... Using an SSG to avoid all chance of hammer bounce.... and combined with the easy cocking of this valve, and all the advantage of a light hammer.... just seems like a natural to me....
I have a gut feel (and that's all it is).... that by using an SSG with the right spring, preload and gap, and a light hammer.... the jet size may become less critical.... a bigger "sweet spot" if you like.... I don't need that, because there is no way I will ever tune more than 10% below the plateau velocity, because I don't want the velocity to rise below the setpoint.... I see NO reason to do that (other than for bragging rights on efficiency, which downslope tunes allow)....
I was asked tonight in a PM how far down the "knee" I tune, and it took me a while to answer, I had to look at a few examples to figure that out.... It turns out the my typical regulated tune is only about 3% below the plateau velocity at that pressure.... If you go down 5%, you start seeing a fair rise in velocity below the setpoint.... The lowest part of the knee I would tune to would be where the velocity peaks 1% above what it is regulated.... This allows extending the shot string 100-200 psi below the setpoint.... When tuning with an SSG, I like to be able to JUST reach the plateau when the gap hits zero.... In the case of the graph above, I'm not quite there, because when I dial in preload I get a 10 fps jump up from 960 to 970.... However, the ART/SS valve has a very "soft knee" to the velocity curve, it takes a lot of increase in the gap to drop from the plateau to the downslope (in this case the cliff).... so I don't need to be able to get to the plateau at zero gap.... With a conventional valve, there is often only a couple of turns of the SSG between the plateau and the downslope.... With most conventional valves, the downslope starts about 7-10% below the plateau velocity.... That means that for any given pressure, the "best" range to tune within is only 10% wide at most.... If you want less velocity, you are better off to reduce the pressure.... and if you need more power, then you have to increase it....
I was concentrating on trying to get a wider velocity adjustment range with the ART/SS valve.... but in fact for use in a regulated gun, a tunable range of 100 fps is all you really need.... I wouldn't be surprised if the same thing applies unregulated.... because just like with a conventional valve in an unregulated PCP.... if you tune the velocity down very much (with a lighter hammer strike), you have to reduce the fill pressure or the ES gets too great.... I looked at a fair amount of my data tonight, and a bell-curve for a 4% ES typically starts about 8-10% below the peak velocity at that pressure (near the top of the downslope).... If you want a narrower ES, you have to start even closer to the maximum.... I have a feeling that the ART/SS valve will be the same....
The Cothran valve has basically no velocity tuning range, it is governed solely by pressure.... A conventional valve can be tuned over a huge velocity range (from flat out to valve lock).... BUT only a small portion of that range is USABLE unless you reduce the fill pressure (or are prepared to accept a huge ES).... Once you realize that everything happens within about a 10% range of velocity.... and to tune outside that range you must change the pressure.... it makes a LOT more sense....
Isn't learning something new wonderful.... I feel like tonight was one of those rare "lightbulb moments".... 8)
Bob
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I had a bit of an epiphany last night about how to tune this valve.... When I looked back over how far below the plateau velocity I generally tune my regulated guns, it turns out that about 3-4% is typical.... By the time you are 5% or more below the plateau, the velocity starts to show a significant increase when the pressure drops below the setpoint.... If you tune less than 3% below the plateau, the gun tends to use more air for not much increase in velocity.... and of course at the plateau it becomes an air hog.... So, this morning I hooked by regulated 500 cc bottle to the .30 cal BRod with the ART/SS valve in it, and did some experimenting.... but I made one (hopefully last) change first.... I made a slightly heavier hammer, that weighs 39 grams instead of the 27 gram I was running yesterday.... This is in between that and the 51 gram hammer I installed in the BRod with the Cothran valve.... The reason for the slightly heavier hammer is that I could not quite get to the plateau velocity with the 27 gram hammer without decreasing the SSG gap below zero (ie adding preload).... which wasted HUGE amounts of air.... I wanted to be able to get to the plateau at zero gap, and adding a bit of weight to the hammer seemed the best way.... and it worked great....
I had checked the output of my 500 cc regulated bottle, and it was actually 1850 psi instead of 1900.... Using that, I plotted a new velocity vs. preload curve with both the 45 gr. and 50 gr. pellets, and got a plateau of 972 fps with the 45 gr. and 945 fps with the 50 gr.... The valve fell off the cliff at 9 turns of gap, with an adjustable range of about 150 fps before it did that.... I tried a few gap settings around 3-6 turns out, and found that at 5 turns of gap, if I let the tank pressure fall below the 1850 psi setpoint I was getting a slight bump in velocity, just as I expected, peaking at about 1780 psi before declining.... That is EXACTLY what I was looking for, my normal tuning point where the shot count is extended a bit below the setpoint pressure, but with a velocity increase of less than 1%.... The problem was, it was occurring at about 940 fps with the 45 gr. and about 880 fps with the 50 gr. pellets, and I wanted a bit more than that.... The solution was to drain the bottle and increase the setpoint pressure a bit.... On the third try I got the shim stack just right, and the new setpoint is exactly 1950 psi.... I repeated the testing with this higher setpoint, with the following results....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%201950_zpsbnmtb6e0.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%201950_zpsbnmtb6e0.jpg.html)
As you can see, the plateau velocity is higher, as you would expect with the 100 psi higher setpoint.... Is it now 988 fps with the 45.0 gr. pellets (97.6 FPE) and 954 fps with the 50.2 gr. (101.5 FPE).... and I can get there with a turn of gap in the SSG.... I found that with 4 turns of gap the velocity didn't increase below the setpoint, but it didn't fall off immediately either, giving me another 5 solid, usable shots below the setpoint.... the velocity didn't drop off until the pressure fell below 1800 psi.... What I had done was tune the gun to act like it was unregulated below the setpoint, with the velocity peaking about 100 psi below the setpoint.... but the curve is so flat at that point, the slight bump in velocity is lost in the SD.... The fact is, I have the gun tuned at 1950 psi, but I can use the tank down to 1800 and never even notice it.... all the shots stay within the normal ES, which is just over 1% (about 12 fps with unsorted pellets)..... The velocity with the 45 gr. pellets is just over 3% below the plateau, and with the 50 gr. pellets it is right at 4% down.... Once again, my preferred tune on a regulated PCP is right around 3-4% below the plateau.... I did one 7-shot mag. as an efficiency test with the 50.2 gr. pellets, and it worked out to 1.25 FPE/CI at an average of 916 fps (93.6 FPE).... This is not as good as yesterday, but the velocity is 30 fps higher, so pretty much expected.... I should still get about 35 shots at nearly 94 FPE with this tune.... and by using a 4500 psi bottle that would more than double....
Bob
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Here is what the .30 cal. looks like assembled....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20BRod%20Wood%20ART-SS%20Valve_zpspnqmnbyh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20BRod%20Wood%20ART-SS%20Valve_zpspnqmnbyh.jpg.html)
It weighs 3 oz. more than the AR version.... The stock is heavier, but the barrel is lighter because of the CF sleeve to bring the diameter of the TJ's liner up to the same as the LW barrel (16mm).... all up with scope and rings it is 9 lbs. 11 oz.... I'm quite pleased with the appearance and ergonomics.... and it balances well, right where you would hold it near the front of the wooden stock....
Bob
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A Wonderful Job Mr. Bob! and a huge At-A-Boy!!! (Texan for congrats) ;D
Knife!
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Bob, that is beautiful!!! What kind of stock is that?
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No idea.... I got it in a box of goodies from Travis last winter when he was cleaning/moving shop.... I think it was intended for a Bullpup, but they are illegal in Canada.... so it became a rifle stock by inletting it for an MRod trigger in the normal configuration.... It is quite light....
Bob
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P12 bullpup stock.
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No, you must be mistaken, Travis.... it's a RIFLE stock (now).... ::)
Bob
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My bad your right Rifle stock.
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I think it look quite nice how its setup right now. I guess its a bullrifle now.
Mike
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I think it look quite nice how its setup right now. I guess its a bullrifle now.
Mike
Bobs Bullrifle That has a nice ring to it.
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There ya go
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P12 bullpup stock.
That's what I thought- Very nice re-hash of it Bob!! I'm liking the semi-bullpup RIFLE set up more and more...
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I spent the last 3 days casting bullets from all the moulds I got from NOE over the summer.... I went through about 20 lbs. of 40:1 lead:tin alloy from Rotometals, and cast bullets in .224, .243, .250 and .257 cal, and one in .308.... One of the bullets I cast was the heaviest BBT designed for .25 cal airgun barrels.... It turned out to be 58.3 gr. in that alloy for the FN version, and 55.0 gr. for the HP.... Here is what one looks like after pushing through the LW Polygonal barrel on my BRod....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/58%20gr%20250%20cal%20BBT_zpstclzsyla.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/58%20gr%20250%20cal%20BBT_zpstclzsyla.jpg.html)
The back of the nose measured 0.250" and the driving band 0.252" before pushing through.... After pushing through the choke, the driving band measured 0.251" across the grooves, and 0.246" across the "lands", but they did not drag on the center portion of the bullet, exactly the way it was designed to work.... At 1950 psi the HP just broke 800 fps, but I wanted to find out what it would do with the SS Valve at 3000 psi, so I swapped parts around to test that.... With the SSG adjusted for a turn of negative gap (preload) I got 952 fps with the FN (117 FPE) with a huge BRRAAAPPPP of air, but I assume that is the plateau velocity.... With a whisker of gap (less than 0.020") the report was normal, nice and crisp (although pretty loud) and I recorded 930 fps for the FN (112 FPE) and 950 fps for the HP (110 FPE).... which is pretty good for the stock length LW barrel of just 23.8".... This gives a pretty good idea of what the SS valve is capable of.... The only way to get more would be to use a retracting bolt to provide unobstructed flow in the chamber, as right now it is the equivalent of 0.234", and I am actually using that for a transfer port diameter, as there is no sense in going larger....
This experiment gives significant insight into what could be done with the ART/SS Valve in .257 cal with a longer barrel, using a 4500 psi bottle regulated down to 3000 psi.... With a 28" barrel, 130-140 FPE should be quite possible, which would enable using the venerable Lyman 257420, which is the benchmark bullet in .257s.... My Hayabusa .257 (3000 psi fill, unregulated) with those specifications (with retracting bolt) reached a peak of 160 FPE, and can be tuned for a very nice string at over 130 FPE.... and that could be increased a bit if regulated to a solid 140 FPE.... There is no reason that the SS valve could not produce the same results, and be a LOT easier to cock as well.... My Hayabusa uses a 115 gram hammer, with a stroke of 1.2", and an 18 lb/in spring.... Cocking force at 160 FPE is 24 lbs.... :o
The experimenting I have done here provides a roadmap for anyone wishing to build a wonderful Varmint or long range target rifle, using proven components.... A 1/2" OD TJ's 25-20 barrel that is 28" long, with a 14" twist, the MRod action (modded for a retracting bolt), with an ART/SS Valve, and a 500 cc CF bottle regulated down to 3000 psi would supply the power.... Tensioning or sleeving the barrel to stiffen it, and maybe a harmonic tuner, should provide the accuracy.... Some decent optics, and an SCBA tank (for refills or tethering), and you would be good for a whole day of serious long-range Varmint busting....
Bob
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Ran some test today with the .25 cal BRod tethered at 3000 psi.... still running the 12 lb/in spring with only 3 lbs. preload.... I was able to just reach the plateau at zero SSG gap as this pressure.... using my 47.5 gr. BBT HPs I got 1002 fps, and with the 50.4 gr. BBT FN I hit 977 fps (106-107 FPE).... At 3.5 turns of gap that dropped to 100 FPE with a nice crisp report.... I didn't check the efficiency.... but those HPs at 970 fps would sure lay a smackdown on anything up to Coyote size, I think....
Interestingly, this is very close to the same SSG setting I was using for the .30 cal BRod shooting 45-50 gr. pellets on 1950 psi.... and only a couple of turns less gap than the .25 cal shooting 34.1 gr. Kings on 1900 psi.... Once you find the sweet spot on the ART/SS valve it doesn't seem to require a lot of adjustment.... even with large changes of caliber or pressure....
Bob
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Yes you have to remove the check valve inside the bonnet of the regulator.... It's nice that Travis made the passages through the drop down so large so that if you use it unregulated the bottle can flow fully into the plenum.... that adds a touch of volume to the plenum, too....
Bob
You're welcome Bob...recall if you will that the porting on that drop down came from the CAD I licensed to those two.
I just got a .25 LW polygon that is going to go onto the second Brod ever made...:) The .22 Brod I have running an other LW polygon is superbly accurate. Whilst sorting the LW site, they have choked and un-choked polygon barrels, but no .294/.300 barrels yet. Would love a polygon for the big JSB's. Given that the .25's are a .254 groove for .250 head pellets, I could see a .296/.302 working very well.
cheers,
Douglas
cheers,
Douglas
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The LW .30 cal barrel is pretty big at 0.298/0.306".... Tim @ Mac1 Airguns tried it and found it an epic fail with the JSB pellets.... WAY too big....
Bob
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All three of the TJ's that have come into my hands have .3015 groove diameters. They shoot quite well...:) Maybe it is time to get after LW for a custom. It is possible; a few small BR manufacturers have gotten .177 polygon tubes with custom twist rates. Just a matter of $$ I suspect, and a really sweet 30 cal pellet barrel would be worth a bit to me. Time to call LW I guess...:) and then perhaps a new thread...:)
cheers,
Douglas
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Last time I inquired (a year and a half ago) the minimum run of custom barrels at LW was 10. There might have been a set up fee as well.
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I have a manufacturer making us custom barrels in different twist rates I’ll be doing some testing soon
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I have more information that would apply to someone building a 6 mm or .257 cal BRod, based on the results from this winter's PCP projects....
https://www.gatewaytoairguns.org/GTA/index.php?topic=128036.300 (https://www.gatewaytoairguns.org/GTA/index.php?topic=128036.300)
The 6 mm with a 29" barrel, regulated at 2800 psi, is getting in the mid 900s with the 64 gr. bullet.... Since the Lyman 257420 is the same Sectional Density (0.155), this means that the idea I talked about above, using the SS valve in a regulated .257 BRod with a similar barrel length can be considered a proven concept using a 500 cc CF 4500 psi bottle.... Starting with a 1/2" OD TJ's barrel with a 14" twist, and sleeving it up to 5/8" with a CF tube inserted into the front of the receiver just shy of the 4-40 screws is completely feasible, although you would have to single load bullets of that length (maybe)....
This brings up a new idea I am working on for longer magazines to fit the MRod receiver, for up to .357 cal.... There are several ways to do this, and here is the first prototype I am working on....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Machining%20Magazine_zpsyf9ab0xu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Machining%20Magazine_zpsyf9ab0xu.jpg.html)
The magazine is shown mounted in a 5C collet in a hex block to enable indexing to drill the holes for the pellet/bullets.... You can see a JSB .35 cal pellet on the right, and a 154 gr. .357 cal bullet on the left (they are sitting on a couple of pieces of dowel to raise them up for the photo).... The material is a piece of 1.25" OD 2024-T3 aluminum bar stock, and it is long enough to make 2 mags.... I am not sure yet how I will mount the mag. and it will likely have to be indexed manually, but one way it could be mounted is on a retractable pin set into the MRod receiver, similar to the way a Hatsan mag. is located.... I checked the width of the mag. slot in a .25 cal MRod receiver, and it is long enough to accommodate that 154 gr. bullet if there is nothing else in the slot, and the barrel is not protruding.... This isn't my plan, I would never want to shoot anything that heavy.... and likely I will make the mag. wheel thinner to help mount and index it.... but it does shown some possibilities....
The other way to make a mag. for a .357 cal. is to copy the MRod .25 cal mag. but with a larger wheel in a similar housing, possibly made by a 3D Printer.... I have drawn one up and sent it to Travis for him to look at.... It would be the same inside length (0.45") as the .25 and .30 cal mags, but that would fit the JSB 81 gr. pellets, the EPP-UGs, and my 109 gr. BBT.... so likely all the length you would need for most .357s based on an MRod.... The advantage to this method is that it would be self-indexing....
Bob
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Well I got sidetracked on the long .357 aluminum mag project.... I had another look at the .25 cal MRod mag. and came up with a different way to modify it for .35 cal and still use the original housing, albeit modified somewhat.... The first step was to make a .35 cal wheel that would fit inside the .25 cal mag. and the only way to do that was to reduce the radius that the holes are on that hold the pellets from 0.50" to 0.45".... This would normally raise the center of the pellet 0.050" above the boreline, but I realized that if I inserted the magazine further to the left, while keeping the feed hole at the same height (which it must be to align the pellet with the bore), I could just rotate the wheel a bit more counter-clockwise (when viewed from the back) to get the height to work out.... here are some photos of the work so far....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Wheel%20for%2035%20cal_zps2bzp0flp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Wheel%20for%2035%20cal_zps2bzp0flp.jpg.html)
The wheel was machined from a piece of MDS, with seven positions, one of which uses a glued in blanking plug that prevents you from closing the bolt when the mag. is in the empty position.... Drilling 7 holes was a challenge with a manual milling setup, the key was to use an online calculator to convert from Polar coordinates (radius and angle) to Cartesian (x and y) coordinates, and then just position the vertical and crossfeeds on the milling attachment on my lathe to drill the 7 holes around the 0.9" diameter circle.... It worked out great, although there was a lot of hand finishing to do, removing the milling flash where the holes broke through the outer diameter of the wheel.... You will notice that the recess in the back of the wheel for the torsion spring is smaller in diameter, so I will need to find or make a smaller OD spring to force the necessary rotation of the wheel to make the mag. self-index....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20with%2035%20cal%20Wheel_zpscjuvn1dg.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20with%2035%20cal%20Wheel_zpscjuvn1dg.jpg.html)
Here is a photo with the wheel in place, but I have not yet moved the feed hole over in the outer casing, or milled away part of the bump stop to make it stop in the correct place.... In the photo below I have machined a larger hole in the clear cover in the correct location.... You can see that it is shifted about 0.090" to the right of the original location.... and you will notice that part of the bump stop will have to be machined away when I mill the hole in the outer housing in the correct location to allow the mag. to slide to the left....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Cover%20Hole_zps2fval8wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Cover%20Hole_zps2fval8wi.jpg.html)
There are lots of things that will remain to be done to make the mag. functional.... the spring as I mentioned, and a new location for the small brass pin that rotates the wheel to allow loading pellets when you rotate the cover.... I will also have to figure out a way to hold the mag. in place, because the slot in the front for the barrel will lose the little bumps that allow the mag. to "snap" into place on the barrel stub.... First I have to get the mag. to function and line up.... then I will worry about the details....
Bob
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I took me many hours and lots of hand work, but I now have a fully functional 6-shot .35 cal MRod magazine, made from a .25 cal.... Here are the photos....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Spring%20and%20Wheel_zpswxb2tw3d.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Spring%20and%20Wheel_zpswxb2tw3d.jpg.html)
The spring is a mess, cosmetically, but it works.... I made it by winding the stock spring around a 9/32" drill bit to tighten the coil enough to fit inside the 1/2" hole in the wheel.... Of course it came out a mess, so I spent a lot of time with two needle-nose pliers tweaking it to get it to work.... ::) .... I had to hand carve the groove for the pin in the cover that rotates the wheel with a tiny burr on a Dremel, and again it may not be pretty but it is functional....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Housing%20and%20Wheel_zps8odtugcl.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Housing%20and%20Wheel_zps8odtugcl.jpg.html)
The housing was milled out with a 3/8" end mill to move the hole over and increase it in size.... There is a 1/32" hole drilled through the filler plug in the wheel for the tail of the spring, which is installed in the photo....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Magazine%20Front_zpsyxqetb4o.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Magazine%20Front_zpsyxqetb4o.jpg.html)
The position of the feed hole, and it's associated recess that clips over the end of the barrel were the key to this project.... They are the same height as in the stock .25 cal magazine, but are moved 0.084" towards the centerline of the mag..... That was necessary for the hole to line up with the smaller radius of the wheel, which was necessary so that the pellets fit inside the housing.... I was concerned about how to retain the magazine in the slot, but as it turns out, that was a non-issue.... When I plunged the 1/2" mill into the front of the housing to create the recess, it left two tiny bumps that slide past the barrel when you insert it, exactly the same as on a stock mag.... The difference is that as you slide the mag. into place, you feel it "click" twice as it slides past the OD of the barrel, once for the stock bumps, and then for the new ones, which are actually tighter than original.... Once in place, the mag. protrudes that 0.084" past the left hand side of the receiver because it sits that much further to the left to line up....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Full%20Magazine_zps9rib7dsb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Full%20Magazine_zps9rib7dsb.jpg.html)
Here is a photo of the loaded magazine.... You can see the brass rotating pin, which I had to relocate, and the enlarged, kidney-shaped loading slot in the clear cover.... It functions perfectly, indexing to the next pellet each time you push one out.... I even tried it sitting on the end of my .357 barrel, and the pellet just slides right into the bore, exactly as it should.... Now that I have figured out how to do this, I will order another .25 cal MRod receiver and bolt, and a PRod trigger group and AR stock so that I can complete a third BRod in .357 cal.... I already have the bottle, tank block, and a spare FLEX tube, and most of the parts to make a valve.... so it looks like a regulated .357 BRod repeater shooting pellets is the next project.... although it likely won't get done until next winter, I am quickly running out of time as spring is here and the Motel will soon be busy....
Bob
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Ya know Bob, if you had asked me a month ago, I would have said you couldn't fit .357 pellets inside the M-rod .25 cal magazine. Glad I was wrong, LOL.
Pretty slick, despite the prototype "appearance". Decreasing the hole diameter for the spring (along with all the other tedious modifications) seems to have done the trick.
Very good.
Lloyd
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That was one of the keys.... The other was to move the hole in the body and cover plate to the right, closer to the centerline of the mag.... so that the vertical height of that hole (which you can't change) lines up with the smaller radius of the wheel required so that the outer edge of the pellets fit inside the body of the magazine.... THAT was actually the key to making it work.... The smaller spring was an obvious requirement, moving the hole over, not so much.... ::)
So when is AirGunLab going to start producing .35 cal MRod mags?.... ;) .... I'll take two, please.... 8)
The only production change I would make is that the clear cover plate is quite thin at the top left of the much larger ammo slot.... Making the edge of the cover a straight line, tangent from the top of the "bump" to the outside of the radius, instead of following the profile of the body, would greatly increase the strength at that point by nearly doubling the width there....
Bob
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I cast up the new NOE pellets today.... The mould comes with 4 sets of RG base pins, and they produce 3 skirted pellets and one solid with a flat base.... They look like this....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/NOE%2030%20cal%20Pellets_zps6857okt2.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/NOE%2030%20cal%20Pellets_zps6857okt2.jpg.html)
The weights in 40:1 lead/tin alloy are 35.0, 37.0, 38.5 and 42.6 gr.... They all chamber perfectly in my .25 cal LW Polygonal barrel, but that is not surprising as I cut the chamber to allow for bullets as well as pellets.... I have my BRod set up with a Cothran valve and the WAR adjustable regulated tank block, set at 1900 psi.... I checked the velocity of all 5 pellets (including the JSBs) and got the following averages for one 8-shot magazine of each....
34.1 gr. JSB = 947 fps (67.9 FPE)
35.0 gr. NOE = 937 fps (68.3 FPE)
37.0 gr. NOE = 919 fps (69.4 FPE)
38.5 gr. NOE = 906 fps (70.2 FPE)
42.6 gr. NOE = 871 fps (71.8 FPE)
I was only shooting inside my shop, with the backstop 20 feet away, and all groups were one ragged hole, with no real difference between any of the pellets.... That is encouraging, because some pellets or bullets can't do that when shooting through the Chrony at that distance.... and those that do usually shoot pretty good at least out to 50 yards....
My summer is taken up with sitting at the Motel reception desk waiting for guests, and we are entering our busiest season now, so it is unlikely I will get to try these at distance any time soon.... but the velocity and energy is right where I want it for testing.... I can't wait....
Bob
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Goodness Bob, that mag is AWESOME!!!
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I'll tell ya'.... you only want to make ONE !!!! …. ::)
Bob
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Honestly, after reading all the work that went into it, I thought the same thing! I'm completely okay with single loading!! ;D ;D
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Perfect project for a 3D Printer, I would think....
Bob
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Perfect project for a 3D Printer, I would think....
Bob
Absolutely! Plus a little water jet cutting for the clear lids... I would think the only real hard part would be to find a supplier for the spring.
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My parts came in today from Joe at DiscosRUs, and I didn't waste any time whacking the front off the Gen2 MRod stock and grinding it out to fit over the WAR tank block.... Here is what it looks like with the Gen2 trigger installed also, plus a 500 cc 3000 psi aluminum bottle....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Gen2%20Stock_zpseu5dsmi0.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Gen2%20Stock_zpseu5dsmi0.jpg.html)
I left the stock long enough to cover the tank block and the bonnet section of the regulator.... There is a bulkhead in the stock JUST in front of the front of the tank block when it is mounted in a WAR tube, so about 3/4" ahead of that is where I made the initial cut, and then ground it to fit with my Dremel....
I also purchased a .25 cal MRod receiver and bolt, which I will be modifying as before to fit the .357 cal TJ's 26" twist barrel I have, with a high-modulas CF sleeve glued over it to stiffen it, like I did with the .30 cal barrel.... I already have a modified .25 cal MRod magazine which will give me a 6-shot .357 cal repeater when it is all together.... I probably won't get much done before the winter, but at least I now have all the parts, other than the valve and hammer which I have to make....
Bob
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Beauty!! I went with the Armada chassis, but I do like the look of the synthetic Gen2 stock! Excellent work as always Bob!!
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The SynRod stock comes with a rubber block that is designed to put some upwards pressure on the tube.... It fits over the boss for the sling swivel.... I moved it back 3 bays so that it is behind the tank block.... At that point, the stock is two different depths inside, because it dips down to create the swell for the back of the foregrip.... The rubber block is the correct height at the back of that bay, but too shallow at the front, so I simply pushed a snug fitting piece of wooden dowel into the moulded in hole that fits around the sling boss, and then ground it down so that it holds the rubber block the same height all the way along.... That way it fits snug against the bottom of the main tube, preventing the stock from moving around forward of the trigger, which it can do without it in place....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Rubber%20Stock%20Block_zpsxcszx2xp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Rubber%20Stock%20Block_zpsxcszx2xp.jpg.html)
I have been looking at what is required for porting for the .357 barrel, and I have decided that I won't be bothering with making an oblong barrel port, since I am building a pellet shooter…. In addition, I plan to try using a short transfer port that only seals against the receiver instead of against the barrel.... The reason for that is that the barrel wall is so thin there is not enough room to create a 3/8" diameter flat on it for the end of the transfer port to seal against, as the flat would break through into the bore.... Travis uses the steel barrel sitting directly on the aluminum receiver (held down by the setscrew above it) to seal, and assures me it works great, so I am going to try it.... The plan is to drill the exhaust port, transfer port, and barrel port all to 9/32" (0.281"), which is 79% of the bore.... That way I should not have any issues loading pellets.... We know that 7mm (0.276") porting is a great mod. on the Korean 9mm's, so 9/32" ports should produce lots of power, especially when heavy bullets are not the goal....
The port is larger than anything I have used on a .357 conversion before (I have never gone bigger than 7/32" on a Disco valve)…. In order to have enough flow in the throat in the SS Valve I plan to build, and not have to use a poppet larger than the 3/8" OD PEEK I made for my recent 6 mm and .257 builds.... I plan to use a piece of 3/32" music wire for the stem, instead of the 1/8" stem which is usual for an MRod valve.... Using a the same 5/16" throat I have used before, this will make the throat area of the valve the equivalent of a 0.298" hole, or about 12% more area than the porting.... which should be enough to compensate for the turbulence around the stem.... I will be using a 1/8" bolt probe, which just fits into the base of a JSB 78 gr. pellet.... In the .357" chamber that leaves an area equal to a 0.334" hole, so the smallest porting will be the 9/32" exhaust, transfer and barrel ports....
Part of the reason for not trying to increase the ports any larger than 9/32" is the restriction inside an MRod valve caused by the small diameter required between the two 4-40 receiver screws.... You can get a bit more area at that point without going wider than the 1/2" maximum ID to leave enough material around the screw holes by using an end mill to make the inside of the valve at that point taller than it is wide.... Here is a photo of an MRod valve I machined out inside to prototype this idea....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Milled%20Out%20Cobra%20Valve_zpseks73xb5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Milled%20Out%20Cobra%20Valve_zpseks73xb5.jpg.html)
With an SS style valve, there is a sleeve around the outside of the poppet, and with a 3/8" poppet the sleeve is about 7/16" OD.... That doesn't leave a lot of room for flow around that inside a 1/2" hole.... hence the reason to mill out that hole larger in height for more flow area past the sleeve.... As you can see, trying to find enough room inside an MRod valve to flow lots of air for a .357 is a bit challenging....
Bob
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Can the Cothran valve's exhaust port be opened to .281" safely?
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No idea.... If so, can the throat be opened up far enough to produce 10% greater (or even equal) port area to that 0.281" exhaust port, with the very thick (0.175") stem.... and if so, what would that do to the delicate balancing act that is taking place in a Cothran valve?.... The throat required would be 0.346" ID or maybe more to flow around that huge valve stem....
Bob
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Hmmm... I'll probably just match all my other ports to the Cothran valve. I'm also only shooting pellets- but I'm aiming for a more sedate 130-ish fpe.
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You should easily reach that with 1/4" porting....
Bob
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I know it has been a while since I posted in this thread, but summer is an impossible time for me to work on airguns because the Motel is too busy.... During the winter, I worked with Travis and Jim designing an adjustalbe regulator to go inside their drop down tank block.... I just received one in the mail today, and it is gorgeous....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg.html)
I got both tank adapters, one for 5/8"-18 UN threads, and one for 18 mm x 1.5 mm threads, so I can use any tank.... The burst disc is on the output side, and is a 3K, as I won't be using more than about 2200 psi.... However, I understand the output can be adjusted higher than that, depending on the Bellevilles installed....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg.html)
It has room for two gauges, the upper one reads output pressure, and the lower one tank pressure.... The adjusting screw is an allen set-screw on the bottom of the block.... It moves the HP seat towards the piston (CW) to reduce the output pressure and away from the piston (CCW) to increase it.... I can't wait to try it out on the tube I have the Cothran valve installed in.... It will be the perfect arrangement for that, because you must adjust the pressure to adjust the velocity....
Bob
Very cool stuff Bob. A lot of info to digest. This block and reg I cannot follow how the fill and gauge on the block connect to the bottle?
Appreciate any hints
Cheers
Walter
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The lower gauge and the fill fitting are on the input side of the regulator (using a small hole, crossdrilled through the block)…. The regulator is installed vertically (from the top) inside the tank block.... You can see the pressure adjusting screw on the bottom of the block.... Backing that out moves the seat lower, requiring the piston to compress the Bellevilles more before the airflow is shut off.... The bottle threads directly onto the brass adapter....
Bob
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Having one on my WARP I have a question...can these reg guts be pulled to shoot unregulated and then reinstalled later to be regulated if wanted? Say slug vs pellet shooter?
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Yes, you could pull out the piston and Bellevilles and leave the seat installed (it is needed to seal the bottom of the tank block)…. and then reinstall the top plug.... You might need something to keep the seat from popping up when fired.... However, the air bleed in the seat is tiny, and so you would still have only the plenum volume of your regulated PCP, the bottle volume would not really participate in keeping up the pressure during the shot like it would if you have large passages through from bottle to plenum.... Between shots, the plenum would reach current bottle pressure, of course, and the gun would be unregulated....
Bob
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Didn't even think of that Bob. Looks like it's staying as is. Thanks for the info! By the way these regs you helped design are arguably the best I've ever used. Incredibly consistent and no creep. Thanks for combining your efforts with Jim and Travis to make them happen!
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Nice Work as usual Mr. Bob!
Wish I could see the pics, but as usual, only a blank rectangle. Very typical from Photobucket.
A LOT easier to post pictures directly from your computer, and much faster! After all, you have to load them into pb, and it is the same here on the GTA. No middle man needed. ;)
Not to mention anyone on the forum can see them. Not just paid Photobucket subscribers. I will not pay them a single red cent. Period!!! >:(
Knife
Knife
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The lower gauge and the fill fitting are on the input side of the regulator (using a small hole, crossdrilled through the block)…. The regulator is installed vertically (from the top) inside the tank block.... You can see the pressure adjusting screw on the bottom of the block.... Backing that out moves the seat lower, requiring the piston to compress the Bellevilles more before the airflow is shut off.... The bottle threads directly onto the brass adapter....
Bob
That is very nice design! Who is the machinist on that block? A lot going on there with critical dimensions in such a compact package!
I love it!
Keep up the good work man.
Walter
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Jim Gaska at Marmot Militia.... I did most of the design work when he and Travis teamed up at W.A.R. (Wicked Air Rifles)….
Bob
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Jim Gaska at Marmot Militia.... I did most of the design work when he and Travis teamed up at W.A.R. (Wicked Air Rifles)….
Bob
Awesome!
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Mr BOB, the pics are now visible on my monitor. Woo-H00!!!
Fascinating thread. 8)
Knife
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Good to hear.... I think your problem was a temporary glitch....
Bob
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Well, the Motel busy season is over for another year, and it's time to hit the shop again.... As promised, the first order of business is to do a .357 version of my BRods…. The parts have been sitting on my bench gathering dust since the Spring.... it's been so long I had to sit down and think about where to start.... ::)
I decided to bore out the receiver for the 0.640" OD Hi-Mod Carbon tubing I used for the sleeve on the .30 cal TJ's barrel, as the .357 liner I have is the same 1/2" OD.... I had a hard time trying to drill it straight, for some reason this receiver just didn't want to run straight in my 4-jaw chuck.... so I drilled it undersize and then held it in my milling attachment, set it up with the bore of the receiver parallel to the ways and lathe C/L, and then used a 5/8" end mill to straighten the hole and move it over so that it lined up with the original 1/2" bore of the receiver.... It took a lot of fiddling, but the result was great, the outer sleeve and the barrel liner both slide into place perfectly.... The counterbored hole for the sleeve is 1.400" deep, so it stops just short of the 4-40 screw holes in the front of the receiver....
I then mounted the receiver across the lathe, in the milling attachment, and centered off the transfer port hole, drilled it out to 9/32" (0.281"), and counterbored it 3/8" x 0.150" deep for the transfer port.... That leaves 0.100" of receiver below the barrel, so the Teflon transfer port will seal against that shoulder with a slight amount of compression against that and the valve.... Travis assures me that you don't need to seal the transfer port against the actual barrel, that the set screw in the receiver that is directly above the barrel port pushes the barrel down against the receiver tight enough to seal OK.... I sure hope he's right about that, as there really isn't enough barrel wall to mill a 3/8" OD flat without hitting the bore.... A .357 barrel with a 1/2" OD only has a 0.070" wall thickness, which is one of the reasons for using the High Modulas CF tubing, to get the greatest stiffness possible for the barrel.... Here is what the receiver looks like at the moment....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20BRod%20Receiver_zpsyorxcggy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20BRod%20Receiver_zpsyorxcggy.jpg.html)
The Teflon transfer port will be 3/8" OD x 9/32" ID.... I chose that port diameter because it is 79% of the caliber, which means I don't have to mill an oblong barrel port, I can just drill it.... It should be plenty big for a pellet shooter, IMO.... The plan is to build my own SS valve, with a matching exhaust port, and I'm going to try for a 0.323" throat on the valve (a size "P" drill), which with a 1/8" stem will give be about 12% more throat area than port area.... Using a 3/8" OD PEEK poppet I will have a 0.026" seat margin, which should work OK.... That will allow me to build the same "guts" for this valve as I did for my 6 mm and .257 valves last winter.... which will reduce the development time....
I'm looking forward to progressing on this build as time permits.... It certainly feels good to get back in the shop again.... It's been a loonnngggg summer.... ::)
Bob
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Looks like a great build Bob! I'm looking hard at the .357 calibers myself, but don't have any machines or your knowledge to build my own. I'll be following along with interest as you post.
Thanks for the TJ barrel work! I really, really like the one I have in my .22. It is so consistent and accurate, and a real joy to shoot knowing it will hit where I aim if I do my part.
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Will continue to follow as well!
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Bob,
Great to see your at it once more ... "Cold" shop & all ... burrrrr
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Oh it's got heat (providing I remember to turn it up in the morning)…. I keep it at 5*C (40*F) at night.... It is, after all, just a garage....
Bob
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Two shop days in a row!.... WOO HOO !!!
Today I modified the .25 cal MRod bolt for this .357 cal build.... Two things had to change, the diameter of the bolt and probe, and the size of the lockup pin.... Crosman use an 8-32 SHCS for the bolt lockup in the .25 cal, and at the same pressure the .357 bolt will have twice the load on it.... Through the threads (the weakest point), a 10-32 has about 50% more shear strength of an 8-32, and I am only using about 2200 psi instead of 3000, so that is what I used.... The bolt is hardened, so I had to heat it to cherry red and let it cool slowly to anneal it.... Once annealed, I could drill and tap the hole out to 10-32 and mill a 1/4" flat for the head to tighten against, and I made a new locking pin from a 1/2" long SHCS with a nut screwed tight against the head to lengthen it.... I turned the head and nut down to 1/4" OD, and shortened it slightly so that it doesn't rub on the tube when the receiver is installed....
To make the larger probe, I used a piece of 3/8" CRS, and drilled it 1/4" to a depth of 3/4" and then shortened the stub of the bolt so that it just slid in full depth.... The OD of the new bolt nose was turned down to 0.356", and I made a longer probe that is 0.125" diameter (which just fits inside a JSB pellet) of the correct length to load the back of the skirt just ahead of the barrel port.... The shoulder between the two diameters I made a 20 deg. taper, which I figured won't restrict the flow, and will slightly reduce the chamber volume behind the pellet.... After taking the photo below of the parts, I installed the new bolt nose with permanent Loctite 638 (green)….
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Bolt%20Parts_zpsf83gzbcv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Bolt%20Parts_zpsf83gzbcv.jpg.html)
The cocking slot in the receiver needed to be widened a bit for the larger pin, and because I use an 8-32 SHCS as my hammer pin.... The front of the slot on the left side also needed machining wider and deeper, to allow the bigger lock pin to properly lock up the bolt.... You can see those mods in the photo below....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Receiver%20Slot_zpsdgrmtkrr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Receiver%20Slot_zpsdgrmtkrr.jpg.html)
The other job I did today was to shorten the barrel and ream a new chamber.... The barrel was previously used in another receiver, but the barrel port position would not work for this build.... I already had a chamber reamer, so all I had to do was stone the cutting edge with a fine grit diamond file and cut the chamber deeper.... I left the barrel in the lathe because tomorrow I will cut the O-ring groove to seal the bolt before removing it from the chuck.... The photo below shows the completed .357 cal MRod bolt, the chamber reamer, and the tool I will use to cut the groove for the 1 mm x 9 mm O-ring....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Bolt%20and%20Special%20Tools_zpsxhcbavae.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Bolt%20and%20Special%20Tools_zpsxhcbavae.jpg.html)
With a little luck, I will have the machining done on the barrel tomorrow, including the new barrel port, and be ready to glue on the carbon fibre sleeve....
Bob
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Bob ,
I’m curious about how you go about glueing the sleeve on the barrel . I’ve done a few 1/2” barrels with 13mm ID tubing . The interference is less than .30” and the green bearing locktite I use tends to wipe off the barrel Asia’s installed into the tubing . The only way I have gotten it to get an OK fill is to spin the barrel into the tube at a fairly high RPM . I’m wondering if there’s a better way .
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I use Loctite 638 (green), and I sand the inside of the sleeve and the outside of the barrel with 220 grit to get a bit of "tooth", then clean both with acetone and blow dry with compressed air.... I coat the outside of the barrel with several full length beads of Loctite, and goop a large ring of it inside the sleeve at one end, and then from that end I slide and twist the sleeve onto the barrel.... I wipe off the excess, and the allow to cure overnight.... The next day I post cure it in my wife's oven at 175 *F for 3 hours....
As long as the sleeve is a nice slide fit over the barrel I don't worry about the clearance.... Loctite 638 is intended to fill a gap up to 0.010" on the diameter.... It might work with a bigger gap than that, but take a long time to cure.... You sure don't want it so tight that you have to fight it to slide together dry, you want the barrel to be able to fall through with its own weight, IMO.... A tight fit decreases the setting time, which is listed at 4 minutes, but I suspect less than that with a close fit....
I would think a 1/2" OD barrel inside a 13mm ID tube should work OK, that is 0.012" on the diameter, assuming those are the actual sizes....
Bob
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Bob,
Your builds and the level of knowledge you incorporate into each one is on a level of it’s own. I truly enjoy everyone you do and learn so much in the process. You’re a valuable asset to this community and I hope others are as appreciative of you and what you bring to the table as I am. So, a big thank you from me.
Peter
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Today I finished off the barrel by machining the O-ring groove, drilling the barrel port, and gluing on the CF sleeve.... Here is what the breech end looks like now....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Barrel%20Port%20O-ring%20Groove%20and%20Sleeve_zpsej9yvnp7.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Barrel%20Port%20O-ring%20Groove%20and%20Sleeve_zpsej9yvnp7.jpg.html)
That 9/32" barrel port is pretty huge, and you can see how thin the barrel wall is with a 1/2" OD and a .357 bore.... I had to sand the outside of the CF sleeve slightly to get a nice slide fit inside the receiver, it was just a bit too snug.... There isn't a lot of room between the barrel port and the back of the barrel, another reason I had to use a tiny 1 mm CS O-ring for the breech seal.... I tried the bolt with the barrel installed in the receiver, and it slides into battery perfectly.... It loads a 78 gr. JSB pellet (which has a slightly deeper base cavity than the current 81 gr. version) nicely past the front of the barrel port.... It should also work perfectly with the new NOE Magnum Hunter pellet with the medium base pin (86 gr.).... The skirt of an 81 gr. EunJin pellet does not quite load past the front of the barrel port, so neither would the 81 gr. version of the NOE pellet which uses the deepest base pin.... I could not use a longer loading probe or it would not retract far enough to clear the mag. well.... This .357 build is really pushing the limits of an MRod receiver, the tolerances are virtually non-existent....
Before assembly with the Loctite 638 I sanded the outside of the barrel and the inside of the carbon tube with 100 grit to give them both some "tooth".... I had a nice slide fit, the barrel fell through the sleeve under its own weight.... Tomorrow, after the initial 24 hr. cure at room temperature, I will give the Loctite a post cure at 175*F for 3 hours.... Loctite is designed primarily for gluing metal, and this post cure makes a huge difference in the bond strength to a non-metallic sleeve.... Cured 638 has a shear strength of 4500 psi, which rivals the best epoxies.... While the barrel is curing I plan to make the new rear tube plug and SSG....
Bob
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Oh my just having one brod but three ;D
Must be a handfull for a aged gentleman like yourself Bob.
Good looking work!
Marko
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This afternoon I finished fitting the barrel to the receiver, adjusting the length of the back of the sleeve to stop the barrel in the correct place for the magazine to fit properly.... I use a 1/2" ID O-ring slid over the barrel against the end of the CF sleeve to provide a bit of resistance, so that I have to push it hard into the receiver to seat it, compressing the O-ring.... It will also seal the barrel to the receiver, should there be any slight leak between the barrel port and receiver port.... That won't help much, as any leak will be directed back towards the magazine, but it can't hurt.... I drilled a hole through the carbon fibre sleeve so that the front setscrew tightens against the steel barrel liner.... After fitting the barrel I fed one pellet from my modified MRod magazine into the barrel, and it worked perfectly.... You could feel a bit of resistance the last 1/8" as the pellet engaged the rifling.... Here is what the pellet looked like when pushed back out through the breech....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/78%20gr%20JSB_zps8fcgppun.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/78%20gr%20JSB_zps8fcgppun.jpg.html)
You can see that the head of the pellet nicely engraves from the lands, but the skirt stops in the parallel portion of the chamber, as intended.... The next job was to make a new rear plug for the tube to hold the SSG I will be making.... This was an exact copy of the one I made for the .30 cal.... Here is a photo.... The bottom grooves are air vents to prevent any vacuum building up behind the hammer on firing....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Rear%20Plug_zps82i1pzhq.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Rear%20Plug_zps82i1pzhq.jpg.html)
Tonight, after dinner, I will post cure the Loctite 638, and tomorrow I should be ready to install the barrel in the receiver.... That will complete the work on the .357 upper.... I still have to make a new SS valve, hammer and SSG for this build.... but I am very pleased with the progress so far....
Bob
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I installed the barrel in the receiver today, and then made a transfer port with a 9/32" ID from a short piece of 3/8" Teflon rod.... I made it to fit the .30 cal lower and accept the .357 cal upper, just for testing purposes.... It sealed up perfectly, and I am delighted to say that Travis was right, it didn't need to seal to the barrel, just between the receiver and valve.... The pressure of the setscrew in the MRod receiver directly over the barrel port presses it down hard enough against the receiver that it doesn't leak when firing, even at 2900 psi.... The valve in the .30 cal lower is an ART-SS Valve with a 0.257" exhaust port, one of the early ones with the 1/4" small end on the poppet, and I am running it with the stock inlet jet, which I believe is a #87.5, or about 0.035".... I have a 51 gr. MDS hammer in place, and the SSG is equipped with an 8 lb/in. spring, with 0.37" of preload (3 lbs)…. Here is what the .30 cal BRod looks like with the .35 cal upper in place....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20Temporary_zps5zryxt6n.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20Temporary_zps5zryxt6n.jpg.html)
I tethered the gun at both 1900 psi and 2900 psi, and tested 3 different pellets, all of nearly the same weight, a 77.5 gr. EunJin, the 78.0 gr. JSB (no longer made) and the newer 81.0 gr. JSBs.... At 2900 psi I also tested a 119 gr. BBT-HP and a Lee 154 gr. RF.... The EunJins were indistinguishable from the 78 gr. JSBs, so they are not graphed in the chart below.... The dotted lines are at 1900 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20ART_SS%20Valve_zpskqhflguz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20ART_SS%20Valve_zpskqhflguz.jpg.html)
At 1900 psi the velocity is nearly maxed out with a slight gap in the SSG (shown as "0"), so the hammer and spring combination is usable as is.... At 2900 psi the velocity increases somewhat with preload on the spring.... With negative 2 turns of gap (about 4 lbs. of preload on the valve stem) the velocity increases 5% with the pellets and about 10% with the bullets.... so either more spring preload on the SSG or a heavier hammer spring would be necessary to allow proper tuning at that pressure.... Since this is just a preliminary test, with a valve I won't be using, I didn't bother making either change, but it shows what the FPE is that is available with a valve with 1/4" porting and a plenum volume of about 85 cc.... With these results, I feel that the plenum is a bit too small for a .35 cal, there is simply too much barrel volume relative to the plenum volume, and this is limiting the FPE.... On this .357 cal, the plenum volume is less than twice the barrel volume.... On the .30 cal it is nearly 3 times the barrel volume, and in .25 cal it is over 4 times the barrel volume....
I got the following results, testing with this valve....
At 1900 psi
77.5 gr. to 81.0 gr. pellets = 131 FPE Maximum.... 125 FPE with a slight SSG gap
At 2900 psi
77.5 gr. to 78.0 gr. pellets = 173 FPE Maximum.... 158 FPE with a slight SSG gap
81.0 gr. pellets = 176 FPE Maximum.... 162 FPE with a slight SSG gap
119 gr. BBT-HP = 191 FPE Maximum.... 161 FPE with a slight SSG gap
154 gr. Lee RF = 194 FPE Maximum....
As a comparison, I previously used this barrel (though 1" longer) on my Disco Double, running a Cothran valve at 2900 psi.... The Disco Double, however, has a 135 cc plenum.... Here were the results tethered at 2900 psi....
78.0 gr. JSBs = 172 FPE.... and at 1900 psi = 132 FPE
127 gr. BBT-FN = 206 FPE
154 gr. Lee RF = 219 FPE
As you can see, the results with pellets are virtually identical.... However, with bullets, the Cothran valve was able to produce a bit more FPE, but that is probably due to the 60% larger plenum volume.... I am hoping that when I make a new SS valve with a larger throat and ports I can pick up a bit more FPE.... However, that 85 cc Plenum will continue to be a limiting factor to the FPE....
Bob
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Today I started working on an SS Valve for the .357 BRod…. I couldn't start with an MRod valve unless I wanted to add a longer seat, because the 9/32" port I want would destroy the valve seat, as there simply isn't enough material there.... I looked in my box of used parts, and I found a scratch built valve body that Travis had sent to me where the seat had been moved forward and the port was on an angle.... The threads in the front of the valve were damaged, but I didn't need those, and after some careful measuring I decided I could probably modify it to work....
The ID of the tube I have is a fraction smaller than an MRod tube, so I had to turn down the OD of the valve a few thou to fit.... I then drilled the front of the valve out to 5/8" ID back to just in front of the 4-40 screw holes.... The hole through between those was already just over 1/2", and you can't go to 5/8", it would break through into the threaded holes and the valve would leak.... That 1/2" hole went right back to the valve seat, but I wanted more flow inside the valve, because the thimble of the SS valve will be 7/16" OD.... So, I bored out the back part of the valve ID to 5/8", using an internal threading tool with a 60 deg. point.... Again, I stopped just behind where the 4-40 holes were, but the part behind them, back to the seat, was now 5/8" like the front....
The middle of the valve was still 1/2" ID, however, so I put the valve in the milling attachment on my lathe, and set it up with the 4-40 holes vertical.... I ran a 1/2" end mill down inside the valve and centered it in the hole, and clamped the crossfeed down.... Now, by using the vertical travel on the vice, I could change the round hole into a vertical slot, that was 1/2" wide and 5/8" tall.... This worked perfectly, and now the inside of the valve is 5/8", except for a couple of small bumps on the sides where the 4-40 screws are....
I then drilled the throat of the valve out to a size "P" drill, which is 0.323", and touched up the valve seat by hand with a 1/2" end mill to make sure it was square to the bore.... I then turned a 3/4" ID recess in the front of the valve to a depth of 0.30", to locate the perforated mounting "wheel" which will hold the front of the SS valve thimble.... The last step inside the valve was to machine a snap ring groove to hold that wheel in place.... I tried a thimble, and there is tons of room around it for flow....Here is what the inside of the valve looks like now....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Inside_zpsbxyg2pbw.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Inside_zpsbxyg2pbw.jpg.html)
I had to enlarge the port from the 7/32" it was to 9/32".... I centered off the existing port, which was on a 20 deg. angle, and enlarged the hole to 1/4" with an end mill.... It was getting pretty close to the seat, and I still had to go larger, to 9/32, so I reduced the angle to 15 deg. and used a 17/64" end mill to enlarge the port.... That left the top of the port nearly 9/32" fore and aft (because of the angle), so I offset the mill 0.010" higher and lower to make the port oval, but because of the angle it appears round.... I then enlarged the recess for the transfer port from 5/16" to 3/8".... The rest of the port work was done with a Dremel, smoothing the transition of the exhaust port into the throat, and making sure the port was a full 9/32" everywhere.... By the time I was done, I could slide the shank of a 9/32" drill into the port all the way to the throat.... Here is what this huge port looks like.... It is 4 times the area of a .25 cal MRod port.... :o
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Port_zpsbw1gx0q5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Port_zpsbw1gx0q5.jpg.html)
This valve was made for a Gen1 trigger, and I am using a Gen2 for this build, so I had to mill two more shallow pockets in the bottom to clear the screws.... I had a poppet for an SS valve I built for my 6 mm left over, so I used it to lap the seat, and it looks like it should seal OK.... Tomorrow I plan to make the mounting wheel for the front of the valve, and using the poppet and thimble I have see if I can get it to seal up.... If so, testing should follow shortly.... For now I will use a 105 gr. steel hammer I have left over from the start of the BRod project, before I tried the Cothran and SS Valves.... It may be too heavy, but it will give me a starting point, and I can always borrow the 51 gr. MDS hammer currently in the .30 cal for testing....My gut feel is that I may need something in between, but that will depend on how easy this SS valve opens....
Bob
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Nice to have time to machine again bob.
How big is the 9/32" in metric? Your imperial dimensions are so weird.
Marko
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I'm interested if there are, say 3/8" and 9/32", do you naturally understand which one is bigger and how much? I mean without calculation.
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9/32" = 0.281" = 7.14 mm = 79% of the bore size.... It is pretty common for guys modifying 9 mm (0.356") airguns to drill the port from 6 mm to 7 mm, and I'm just a whisker larger than that in this .357 cal build.... It's about as big as you can go without creating possible loading problems with pellets, and even at that diameter, you have to do a really good job of deburring and rounding the edge of the barrel port....
I grew up using fractions, and the easiest way to think about it is to think of a drill index, where they are arranged in order, by 1/64" increments.... I admit I have to scratch my head sometimes to remember the 64th's, but it's pretty easy to know "intuitively" where you are in size if you take the 1/16" increments (everybody can remember those, right? ) and then multiply the numerator in your head by 2.... For example, 5/16" is bigger than 1/4", if I want the one in the middle, it will be in 32nds, so double the 5 to get 10 and subtract 1, so 9/32 is halfway between 1/4" and 5/16".... If I need the 64th size larger than 9/32, then double the 9 and add one.... The answer is 19/64, so that is one drill size larger than 9/32"....
When I am doing calculations for area, I revert to using decimals, but without grabbing a calculator, I couldn't tell you what the decimal equivalent of 19/64 is (0.297")…. Metric might be easier, if you are working with it all the time, and have all the Metric drills in 0.1 mm increments.... but I don't, my Metric set is only every 0.5 mm.... Then I also have sets of "number" drills and "letter" drills, which have 2 or 3 sizes in between the 1/64" increments.... Generally, I can find a drill within 0.005" or less of any size I need, up to about 3/8" (10mm)….
Bob
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You hogged the heck out of that Mrod Valve! It should flow air like crazy.
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I worked on the inside of the valve today.... I had a poppet and thimble from the first SS valve I made, using the dimensions Lloyd used on his prototype.... The small end of the poppet is VERY hard to machine without breaking it in Delrin, so this one had a brass body with a Delrin overlay.... I have since changed the dimensions, which Travis did too.... in my case to make it easier to machine.... Here is a photo of the parts.... Note the air passage ground into the shaft which vents the area between the O-rings to the exhaust port, that is key to its operation....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Thimble%20and%20Poppet_zpsfwyaryct.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Thimble%20and%20Poppet_zpsfwyaryct.jpg.html)
Last year I avoided showing any photos of the inside of my SS copy, to protect Travis' investment.... but there have been a few photos posted, and I think most people know what it looks like inside, so I figured there would be no problem sharing what I made myself.... In addition, Travis gave me permission to make a generic drawing of an SS valve to include in the next article I am writing for HAM on balanced valves, thanks Travis.... Here is the completed SS valve.... The valve stem is short enough that the hammer cannot drive the poppet to the end of its travel, which could damage it.... I still have 0.200" of travel....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Complete_zpsb7hcivgs.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Complete_zpsb7hcivgs.jpg.html)
Here is a photo of the front end, showing how the thimble is mounted, secured by the snap ring.... The way I build the wheel allows a small amount of radial movement for the thimble, so that it can self align with the poppet....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Front_zpsjndczq3k.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Front_zpsjndczq3k.jpg.html)
Note the vent hole in the mounting screw.... This allows HPA to enter the front of the thimble, in front of the small O-ring.... The spring only needs to be strong enough to overcome the friction of the O-rings and seal up the valve for initial filling.... Travis uses adjustable jets instead of my fixed 1/16" vent hole, to allow for fine tuning....
Unfortunately, this version didn't work.... The Delrin part of the poppet came loose on the brass rod.... I had another poppet, with a larger front end, that I had made for my 6 mm, but I didn't have a thimble for it.... I made a new thimble, and reassembled the valve.... It STILL leaked.... By this time I was tearing out what little hair I have left.... ::) …. I tried lapping the seat, replacing the O-rings, I even turned the poppet sealing face to re-true it, but the leak got worse and worse, lots of air coming out the exhaust port.... I eventually figured a way to test the O-rings on the poppet, and there was no air leaking out the back of the thimble or through the vent hole, so the only place left was the seat of the valve.... I spun the poppet with a drill to leave a polished ring on the seat, and it was off center, relative to the valve throat.... When I drilled out the throat I guess the drill tended to follow the exhaust port and ended up off center.... Since the sealing margin is so small (0.323" throat and 0.375" poppet) I guess there isn't enough seat on the side nearest the exhaust port, and that must be where it is leaking.... >:(
This is about the hardest thing to fix, unfortunately.... I can either make an entire new valve body, or try to repair the one I have.... Since I have a lot of hours into this one, I'm going to try and fix it.... Tomorrow I plan to make an insert for the back of the valve, with a new throat, seat, exhaust port and valve stem guide hole, and try and get it all straight and centered.... Then I will have to machine out the back of the valve body to install it.... There are a couple of different ways to do this job, I'll be pondering that overnight....
Bob
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Very nice!
Hey Bob quick side question, how long are the shortened airtubes?
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The tubes Travis sent me are 11.75" LOA, and drilled for a Gen2 trigger group.... However, they can be drilled and tapped to accept a Gen1 or PRod trigger.... The rear caps are different as well.... They are threaded at the front to accept a stock MRod fill fitting, or a WAR tank block....
Bob
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Thanks Bob! Crazy that they can still make that much FPE with only that much air in the plenum...very impressive!
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The total volume of plenum plus valve is about 85 cc.... plenty for a .25, OK for a .30, but on the small side for a .35 with pellets.... For .357 cal bullets, it is a LOT too small....
Bob
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Well I wasted all morning trying everything I could think of to get this thing to stop leaking.... I finally decided to bore out the back of the valve and replace the seat and valve stem hole with an insert.... When I started boring out the back of the valve I heard a strange scraping noise, and found out why it has been leaking all this time.... Travis must have made a seat insert to move the seat forward, because my end mill caught it and spun it around in the valve body.... I pushed it out, and this is what I found....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Valve%20Seat%20Insert_zpspymkswzu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Valve%20Seat%20Insert_zpspymkswzu.jpg.html)
So the air leak I had tracked down to the poppet on the seat was not the problem at all.... The air was leaking around the sides of this insert and then escaping out the exhaust port.... It may not have leaked when Travis installed it, but by the time I hogged out the ports, there was obviously a crack opening up between the OD of the insert and the ID of the valve body.... ARRGGGHHHH!!!!!....
Anyways, I used a 9/16" end mill, working from the back of the valve, to mill out the inside all the way to (and removing) the seat.... I then had to make an insert, sealed by 2 O-rings, and retained by the three valve screws and a setscrew in the top.... It looks like this.... The insert is upside down, relative to the valve in this photo, so you can see the throat and port better....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Insert_zpsmhin6noz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Insert_zpsmhin6noz.jpg.html)
There was hardly any room between the seat and the front of the port, so I had to use a thin Metric O-ring and stretch it into place in a narrow and shallow groove.... I hope there is enough material between the groove and the port that it doesn't fail.... There is quite a bit of load on this part (510 lbs. at 2000 psi) so after I installed a setscrew in the top I drilled down and tapped the three valve screws to retain it.... It isn't going anywhere.... ;)
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Insert_zpszm4hdslf.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Insert_zpszm4hdslf.jpg.html)
If you look closely, you will see a thin, shiny ring around the throat of the valve.... I spun the poppet around with a drill to lightly polish the seat, and make sure it was centered and had a wide enough overlap.... I don't think there should be any further problem getting this valve to seal, although sliding the insert into the valve body without slicing that tiny front O-ring may be a challenge.... ::)
I've had enough frustration for one day.... Tomorrow I will find out if I finally got this valve to seal up.... ???
Bob
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I assembled the valve very carefully today, making sure I didn't damage the small front O-ring on assembly, and I'm please to say there was no leak between the new insert in back end of the valve and the valve body.... I had to disassemble one more time to lap the poppet to the new seat on the insert, and I'm please to say that I now have NO leaks.... Having assembled the tube successfully, I decided to put the rest of the gun together and test it.... I ran into one slight problem, the Gen2 trigger sear was a fraction further back than the Gen1, and the hammer wouldn't latch, so I had to turn the tapered sear catch on the front of the hammer down slightly to shorten the effective length and cocking distance about 0.030".... That did the trick.... I did some tethered testing, rebuilt a regulator for a 2200 psi setpoint, and then assembled the gun for the first time.... I used my 105 gr. steel hammer, because of the larger ports, and it worked great....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20BRod%20Testing_zpsiaeglrjy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20BRod%20Testing_zpsiaeglrjy.jpg.html)
The "tiny tank" is what I use for testing and setting regulators, but it allows me to tether using the regulator I will be using on the gun.... and not have to waste a 500 cc bottle of air should I need to disassemble it.... Anyways, here are the results of both the tethered testing, and regulated at 2200 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20Big%20SS%20Valve_zpshqho4qvr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20Big%20SS%20Valve_zpshqho4qvr.jpg.html)
I tested using the EunJins (I want to use them up and save the JSBs where possible)…. Initial tests at 1900 psi tethered showed the larger ports increased the velocity from 854 fps to 906 fps, an increase of 16 FPE.... slightly better than the difference in port diameter would have predicted, so I am very pleased with the new valve.... My Great White was just under 2900 psi, so I couldn't tether at that pressure.... I just connected directly to it, and tested the EunJins at 2800 psi, then the 119 gr. BBT HPs at about 2750, and lastly the 154 gr. Lee FN at 2700 psi.... Even though the pressures were less than the original testing I did with the ART-SS Valve with the smaller ports, I had higher FPE.... The 154 gr. bullet hit 202 FPE at just 2700 psi, so I am quite please with the way the new valve works.... With the 154 gr. I gained 15 fps at 200 psi lower pressure with the bigger ports.... 8)
I then fitted the 2200 psi regulator with the "tiny tank", and tested with the EunJins and the 81 gr. JSBs (black line above).... With just a whisker of gap in the SSG I got 158 FPE, right what I was hoping for.... With the SSG backed out 3 turns (about 0.17" gap) the gun was shooting right at 150 FPE average with the two weights of pellets.... I shot a 10 shot string with the 81 gr. JSBs, and the ES was only 11 fps, with a low of 910 and a high of 921.... Seven of the 10 shots were 913-917 fps, so the valve is VERY stable.... The average was 150.7 FPE, and the 10 shot string dropped the pressure in my Great White by 41 psi (measured with a digital gauge)…. so the efficiency was 0.97 FPE/CI.... That should give me very close to 2 magazines (12 shots) at 150 FPE when I fit the 500 cc bottle and fill it to 3000 psi.... I can play with the SSG adjustment, and with hammer weight (I can go a bit lighter) to get the best balance between power and efficiency....
All in all, I am delighted with the way this project turned out.... The plenum is a bit small, and if it was increased to 1 cc per FPE the gun would likely hit about 160 FPE at the same setpoint pressure and air use, with greater efficiency.... I rather expected that to be the limitation on the performance.... and it looks like I was correct in my prediction, for both that, and the overall performance.... I hope next Spring I can find time to test it properly....
Bob
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Bob ,
Great work as usual. I’m glad you posted a pic of your home brew SS valve . I had a good idea on how to build one but the passage between orings had me stumped . Clever way to get it done with a channel into the shaft. Are you using delrin as the valve poppet ?
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WOW!!! ;) 8)
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My later valves use a drilled hole, parallel to the stem and very close to it.... There isn't a lot of room between the stem and the bottom of the O-ring groove on the large end of the poppet.... Using a 1.2 mm CS Metric O-ring helped.... I have used both Delrin and PEEK for the poppet.... The loads are much lower than a conventional valve of the same throat diameter and pressure, so Delrin should in theory be the right choice.... However, the PEEK was easier to machine because it is stronger/stiffer and it is a pretty small part.... and seemed to seal up just fine....
Bob
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Today was consumed with all the little finishing touches on the three BRods…. I had a slow leak in the new .357 cal, which I found was a leaking plug on the bottom of the WAR tank block.... I had glued in that plug with JB Weld, and there was a slow leak spiralling up the threads.... Since I had glued the plug in, I had to heat it with a torch to break loose the epoxy, and once I got it out and cleaned it up, I shortened the plug 1/16" so that it would miss the ASA threads.... I had previously retapped the plug hole, and I went too deep, and the plug was interfering with the ASA threads.... I also removed the male Foster on the tank block and replaced it with a plug, since you fill the bottle through the regulator.... I sealed the plugs with Teflon tape, and that seems to have done the trick.... Once I had that done, I installed the 500 cc 3000 psi bottle, filled it to 3000 psi, and set it aside....
The .30 cal was leak free, so all I had to do was remove the male Foster on the tank block and replace it with a plug.... After a leak and velocity check, I also installed the bottle on that gun, and also filled it to 3000 psi.... Then it was the .25's turn, and I knew it had a serious leak....
It turned out there were actually three leaks, and it took me half a day to repair them.... The first two were easy, a loose plug and a loose gauge.... It was still leaking, so I stripped the gun down completely and replaced the valve O-ring.... but it wasn't that either.... Eventually I tracked it down to a leaking gauge, and once I replaced that it seems to hold air OK now.... I checked the velocity, and it was still what I wanted, so I installed the bottle on that one too, and filled to 3000 psi....
Here is what they look like, now that they are finished.... All three BRods use a modified .25 cal MRod receiver, bored out forward of the front 4-40 screws to accept a 5/8" OD barrel.... They all use a 500 cc, aluminum, 3000 psi bottle for the reservoir, and an SSG to control the hammer.... and have two gauges, one for the bottle pressure and one for the plenum pressure.... The main tubes are from WAR, I believe they were for the FLEX, and yield an 85 cc plenum, including the valve volume.... The tank blocks are also from WAR.... All of them use .25 cal MRod magazines and bolts, modded as necessary....
(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Three%20BRods_zpszyubd9gu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Three%20BRods_zpszyubd9gu.jpg.html)
The top one is the .357 cal.... It uses a Synrod stock, and a Gen 2 trigger.... The barrel is a 1/2" OD, .357 cal, 26" twist TJs, 27" long, glued inside a high-modulas Carbon Fibre sleeve for added rigidity.... It has a steel hammer and a homemade SS valve, and the porting is 9/32" (0.281") or equivalent throughout…. The bolt nose is sleeved up to .357 cal, and the lockup lug is inceased to 10-32 for additional strength.... The mag is a 6-shot one-of that I modified myself....The regulator is mounted on the bottle, and set at 2200 psi.... This results in 2 mags (12 shots) at 146 FPE, using the 81 gr. JSBs at 900 fps....
The one in the middle is the .30 cal.... It uses a modified Bullpup stock that was a gift from Travis, and a Gen1 trigger.... The barrel is a 1/2" OD, .300 cal, 26" twist TJs, 25" long, also glued inside a high-modulas CF tube.... It has an MDS hammer and an ART-SS valve, one of the first production ones with the smaller poppet front end, and the porting is just over 1/4" (0.257") or equivalent throughout.... The bolt nose is sleeved up to .30 cal, and the lockup lug increased to 10-32 for additional strength.... The mag is a 7-shot from AirGunLab…. The regulator is also mounted on the bottle, and set at 2000 psi.... This results in 4 mags (28 shots) at 98 FPE, using the 50 gr. JSBs at 940 fps.... It will shoot the 44.8 gr. JSBs at about 980, and the 59 gr. NOE Hunter Magnums at 880 fps (101 FPE)….
The bottom BRod is the .25 cal.... It uses an airsoft AR stock, on an adapter that I made myself, and a PRod trigger and grips.... The barrel is a 5/8" OD, .250 cal, 17.7" twist LW, 23.8" long, with polygonal rifling.... It has an MDS hammer, and one buffer O-ring between that and the Cothran Powerhouse valve, with 0.257" or equivalent porting throughout, including an oblong barrel port.... The regulator is adjustable, and mounted in the COBRA tank block.... It was a sample from WAR, as I helped them design it, and is set at 1800 psi.... Having an externally adjustable regulator is nice with the Cothran valve, as you have to change the pressure to change the velocity.... This gun delivers 6 mags (48 shots) at 65 FPE, using the 34 gr. JSBs at 930 fps.... It is easy to increase that, or to reduce the pressure to about 1400 psi to use the 25 gr. JSB Kings if desired.... The way it sits, it will launch the Kings at about 1030 fps, which is way too hot....
This has been an interesting project, and I'm happy to say met all the goals I had.... I did some testing with bullets, running unregulated at 3000 psi, and while the performance was remarkable, I think they are much better guns regulated, and shooting pellets.... I hope to be able to do some testing next Spring, after the snow melts.... I must thank Travis for the big box of "spare parts" he sent me when he moved shop a couple of years ago.... Without that, these three BRods would have never materialized.... 8)
Bob
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How much of an effect do the air strippers have on the accuracy
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My previous experience is that when tuned for optimum gap, they help a bit.... and when wrong, make things worse.... I guess you could say that makes them worthwhile.... On these BRods, that determination will have to wait until at least the snow is gone (best case), and maybe until 2021 after we close the Motel (worst case)…. ::)
I couldn't put one on the .357 because the Hatsan ones (which I use) have 1/2"-20 threads, and the barrel wall is too thin with that bore size....
Bob
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All 3 guns are very, very nice!!!
Someone used the word crafty. You certainly solved a bunch of problems in ways that make sense and work well. Easier said than done.
All Hail Bob Sterne!!! https://thumbs.gfycat.com/GrayOptimisticChanticleer-max-1mb.gif
Steve
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*LOL* @ the .gif....
Bob
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I haven't done any work on these BRods for about 5 years, just taking them out to shoot once in a while, and using them for testing pellets and slugs over my LabRadar.... However, my son showed up for a Grouse hunt, so I set up the .25 cal to shoot 34 gr. JSB King Heavies at 950 fps, regulated at 2000 psi, and he is a happy camper!.... Since this year .35 cal and over airguns are now legal for hunting deer in BC, he asked if the .35 cal BRod could be used for that.... I told him it was set up for pellets, and the magazine was too short for heavy enough slugs for deer, but while sleeping I thought "Why not 3D print a 3 shot shuttle magazine", and convert the gun to unregulated, to shoot .357 slugs....
So, a few prototypes later (to get all the proper fits between the parts, gun and slugs), I had one that worked properly.... I shortened the bolt probe 0.100" because slugs have a flat base instead of a hollow in the skirt (so the pellet probe was loading slugs too far forward), and removed the regulator.... After decreasing the gap in the SSG to work with the higher pressure, and playing with the adjustment, I got a perfect 3-shot string, followed by a gradually dropping velocity.... This is with 127 gr. FN slugs from Accurate, sized to 0.356"....
(https://hosting.photobucket.com/images/oo221/rsterne/BRod_357_Unregulated.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/BRod_357_Unregulated.jpg)
The first 3 shots are just over 200 FPE, and the 10th shot is 180 FPE, so a great tune for deer.... The 3-shot magazine turned out equally well, here are some photos.... First the 3D printed parts (made from PETG)....
(https://hosting.photobucket.com/images/oo221/rsterne/Magazine_Parts.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Magazine_Parts.JPG)
The shuttle has internal O-rings in the holes to keep the slugs from falling out.... I printed the groove elliptical so that the #012 O-ring were flush on the side, and only touched the slugs top and bottom.... They stay in place but the O-ring does not interfere with loading or chambering....
(https://hosting.photobucket.com/images/oo221/rsterne/Shuttle_Showing_O-rings.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Shuttle_Showing_O-rings.JPG)
The holder for the shuttle just snaps in place.... It sits over the barrel stub (that normally locates the magazine in an MRod), and there is a 1/4" O-ring in the top of it protruding about 0.010" to act as a detent for the shuttle in the center position....No detent is needed in the end two positions, the shuttle has stops to make sure the chambers line up with the bolt.... One end stop is removable for assembly/disassembly....
(https://hosting.photobucket.com/images/oo221/rsterne/Holder_in_Place.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Holder_in_Place.JPG)
When the mag is centered, both outer chambers are available for loading, simply insert the slug from the rear....
(https://hosting.photobucket.com/images/oo221/rsterne/Mag_Centered.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Mag_Centered.JPG)
When you push the shuttle to one end, you can load the center chamber....
(https://hosting.photobucket.com/images/oo221/rsterne/Mag_to_Right.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Mag_to_Right.JPG)
and the other end is flush with the receiver....
(https://hosting.photobucket.com/images/oo221/rsterne/Mag_Flush.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Mag_Flush.JPG)
We are both delighted with the results, and my son gets to enjoy a couple of my custom projects.... A win-win-win situation for everyone.... 8)
Bob
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Pretty danged cool! 8)
Do let us know if he gets a deer with it.... :D
Jesse
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+1 very interested to hear about his adventure as well. Nice guns Bob.
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Of all threads, I have probably borrowed more tips from this one than any other. I really didn't think there was more for it to give, but you somehow opened another chapter. Great job, I look forward to seeing more.