GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on April 27, 2013, 04:50:44 PM
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Over the past few weeks I have been collecting the necessary parts for this new project.... Here is what I have purchased as a starting point.... I bought a Disco main tube and valve, the hammer and gauge block from a PRod, a trigger and guard from an MRod, a Disco Double kit and MRod trigger shim from Lloyd at Air-Gun-Lab, and a Boyd's Blaster stock in Camo from Norm at Discos-R-Us inletted for the Disco Double kit and MRod trigger.... I wanted to start from the best possible components to achieve my goal....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3295_zpsad124e3a.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3295_zpsad124e3a.jpg.html)
The main purpose of this project is as a test bed for the new .30 cal barrels that SeanMP and I are having made for the new JSB .30 cal pellets.... These pellets are smaller than the 0.308" standard used by Powderburners, having a head size of only 0.300", so we have designed a new barrel to match.... They will be available in a 25" length to fit on the Disco and allow enough room for a muzzle brake or air stripper to be attached.... The barrels will be 0.50" OD, which will allow their use in a .25 cal MRod as well as a new repeater breech that I have designed and Sean will be making.... The breech will also accept a .25 cal barrel with a 0.50" OD, and make use of the 8-shot .25 cal MRod magazines, both stock for the quarterbore version, and enlarged to .30 cal (with 7 shots) for the bigger caliber.... The magazines will accept pellets or cast bullets up to 0.48" long.... Those can be stabilized in a .30 cal barrel with a 26" twist, which is ideal for the JSB pellets, so that was our choice.... The mandrel had been made, and we will be placing an initial order shortly....
In terms of potential performance, we're pretty much flying blind here at the moment.... My initial goal was ~850 fps with the 46 gr. JSBs (74 FPE), and while that remains a realistic performance level to get a decent shot count, I'm hoping that during development I may see that power level in .25 cal and about 88 FPE in the .30 cal, but at what pressure remains unknown.... Ideally, I would like to achieve 14 shots (2 clips) with the .30 cal using the Disco Double tube setup.... which would mean 7 shots (1 clip) on a standard Disco.... As the market for quarterbore rifles is likely way larger than for a .30 cal, we are trying to reach a compromise between the two, allowing as many components to be shared as possible.... and also for the minimum changes to Disco components.... It's a given that the valve needs to breathe a lot better, so that will be the place I start.... I will try the PRod hammer (without the extended striker) and my heavy Disco hammer spring, but I doubt they will be up to the job, so we anticipate making a heavier hammer with longer travel, and using a QB hammer spring to move enough air, particularly for the .30 cal.... An RVA will be part of the package, of course....
The new 7/8" wide, 6" long breech will be designed around the .25 cal MRod magazine, and will incorporate an additional mounting band at the front, located between the trigger and gauge.... This will provide exceptional rigidity for a floating barrel, although a barrel band may also be used if desired.... The top of the breech will be grooved full length for dovetail mounts.... It will be significantly taller than a Disco breech (to allow for the magazine), so for appearance it will incorporate a mount for a 7/8" OD Carbon Fibre shroud and a Hatsan-style air stripper.... The end of the barrel will be threaded, and when the air stripper is tightened against the end of the shroud, it will put it in compression, putting the barrel in tension.... The muzzle blast will be vented out through the stripper, and not into the shroud, so that legality will not be a question in Canada.... For those allowed to have quieter airguns, there will be clearance for a longer 1" OD shroud.... although the barrel tensioning feature will be lost of course.... It is hoped that 0.59" OD barrels will be available for QBs and Sean may even work on a repeater breech for them as well at some future date....
While we're on the subject, I want to make it clear that I will not be involved in the marketing of these barrels, breeches, and other components other than in doing the design work and prototyping.... Manufacturing things and selling them is Sean's bag, not mine.... so I ask that any inquiries in that regard be addressed to him.... My compensation is solely the satisfaction I get from making things work they way they should.... at which point I move on to the next project.... I have no interest in repetitive operations, nor do I have the time to do them.... I have purposely not put this thread in the Big Bore gate, because it will also be talking about the .25 cal version, and also because I felt it would get more traffic here....
Bob
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Keep us posted. looks like an awesome project. You are starting with the best components which will make a big difference.
I noticed that you gauge does not look like a disco guage. I have been looking to upgrade my guage to a more accurate. I would love ti find a 3000 psi guage with 200 psi increments.
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bob
i assume this new barrel will work with the bnm breech ?
ive been thinking about making a single shot tray for it and with the 7in airtube extension and a double tube that is 7in longer and me wanting a long range gun. i think i have enough air on hand for a very powerful 30cal with a good shot count. so my interest is peaked that is for sure.
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Rdsail.... The guage is from China, 3000 psi with 200 psi increments.... I have had problems with some of them and would not recommend them.... McMaster Carr makes a 4000 psi gauge with 200 psi increments but I haven't tried it yet....
Mike.... I understand that BNM makes a breech for the 1/2" OD MRod barrel.... If that is the case, then it would fit, as the new blanks will be that diameter.... The plan is to make 25" the default length, but it could be shortened to 20" like the MRod no problem, and I believe Sean will be making "drop in" .30 cal MRod barrels.... The barrel porting for the Disco Double is going to be larger, of course, but that is something you would want to change anyway for the larger caliber.... We will be using a transfer port made from a piece of 5/16" OD Teflon rod with a 3/16" hole in it, or possibly 13/64".... I don't know if the BNM breech can be modified for that big a transfer port or not, I've never seen one.... When you see our breech, I'm not sure you would care, with the more rigid mounting (like my Hayabusa breeches).... *wink*.... Longer barrels (up to ~30.5"?) can be ordered.... and Sean even has the ability to roll in a choke if you desire.... all for extra $ of course....
Bob
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Looks real nice. What are you wanting to kill with 74-88fpe? Desiring 100yd+ kills?
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Should be a decent Coyote gun, and should anchor 'Chucks instead of them making their burrows as often happens with a .25 cal and almost always with a .22, it seems.... The range will be determined, as always, by the accuracy.... I don't have a BC on the new JSB .30 cals, but they are basically a scaled up King plus a bit, so the SD and BC should be about 27% higher.... in the 0.043 - 0.045 range.... 88 FPE at the muzzle would end up about 50 FPE at 100 yards, so you're talking decent .25 cal power at the muzzle, but at 100 yards instead.... Sighted at 50 yd. the drop at 100 should be about a foot....
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Well considering that people here are getting clean yote kills with .25 mrods at lower fpe than that I'd guess that yours will be better than decent. 50fpe at 100yds sounds like a great air gun to me. ;)
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As I said, the first thing that needs to be done is to improve the flow through the valve.... A stock Disco has the following port dimensions, starting at the barrel and working backwards against the flow....
Barrel Port - 0.133"
Transfer Port - 0.140"
Exhaust Post 0.146" (90* corner)
Throat ID - 0.219" : Stem OD - 0.156" - {Equivalent diameter - 0.154"}
Valve ID - 0.514" : Poppet OD - 0.428" - {Equivalent diameter - 0.285"} (radial gap 0.043")
Inlet ID - 0.250"
Gauge Port ID - 0.125" (PRod Gauge Port ID - 0.343")
As you can see, in a stock Disco, the narrowest restriction is the gauge port on the inlet side of the valve.... Replacing this with a PRod gauge port makes the inlet side virtually unrestricted compared to the outlet, with the smallest diameter being the inlet of the valve itself at 0.250".... The porting on the outlet side is relatively well balanced, with the smallest point being the barrel port itself, which is 0.134" in both .177 and .22 cal.... I find that making the barrel port larger than 75% of the bore size can lead to loading problems or damage to the pellet.... The 0.134" barrel port is therefore the maximum width that can realistically be used in a .177.... In all other calibers, making it (and the other ports feeding it) larger can provide increased airflow, and hence offers the potential for more FPE.... These "75%" port diameters are as follows:
.20 cal - 0.150"
.22 cal - 0.163"
.25 cal - 0.188"
.30 cal - 0.225"
.35 cal (9mm) - 0.268"
From past experiments on Disco valves, I have determined that there is enough meat around the exhaust port to run a 3/16" mill in at a 20* angle (although in .22 cal, I use a 5/32" mill).... greatly increasing the area and easing the 90* corner at the throat.... The flat where the transfer port seals can be increased slightly to a 5/16" diameter, and I have had great success making transfer ports from 5/16" OD Teflon rod with a 3/16" or fractionally larger hole.... Taking into account various production considerations, and the fact that we're not trying to throw 100+ gr. cast bullets downrange in the .30 cal, we decided to design around the optimum 3/16" barrel port in .25 cal.... I basically started at that barrel port and worked my way back from there, making sure there was more flow at each stage, and ended up with the following dimensions....
Barrel Port - 0.188" (double the area)
Transfer Port - 0.188"
Exhaust Port - 0.188" x 0.202" - {Equivalent diameter - 0.195"} (70* angle with rounded corner)
Throat ID - 0.234" : Stem OD 0.115" - {Equivalent diameter - 0.204"}
Valve ID - 0.625" : Poppet OD 0.428" - {Equivalent diameter - 0.455"} (radial gap 0.098")
Inlet ID - 0.266"
Gauge Port ID - 0.375"
I decided that rather than use the PRod gauge port I would make a new extended valve front end with integral gauge mount.... One of the things that is problematic with the Disco design is that you have to slide three O-rings past the 1/2" diameter hole in the tube where the gauge is installed.... This large hole tends to act like a cheese grater and often damages the O-rings.... By making the gauge port and the valve front end in one piece, the O-rings are in front of that hole and don't get shredded.... The only downside is that each front end has to me made to match the valve back end it is used with because of "thread clocking".... However, that's Sean's problem, not mine, I only have to make one....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3301_zpsaf6963b1.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3301_zpsaf6963b1.jpg.html)
In the above photo you can see the slimmed down valve stem, and then extended valve front with 1/8" NPT gauge mount.... The small recess aft of that is for the front trigger mounting screw, which protrudes inside the tube when installed.... Notice that the O-rings are in front of the gauge mount....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3305_zpsabcb7292.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3305_zpsabcb7292.jpg.html)
In this photo, you can see that the front of the gauge portion is opened out to 1/2" for a bit of increased volume, and you can see the huge 3/8" hole through it for most of its length.... Note that the valve rear half is bored out to 5/8" from the seat to within 0.3" of the front, vastly increasing the volume inside the valve, but that was mostly done to ease the flow around the head of the poppet.... Although from an area point of view there wasn't a problem, I have a gut feeling that trying to cram that much air through a gap not much more than a millimeter wide and then forcing it to turn twice through 90* has to produce extra friction.... Therefore I bore out my valves to ease the flow past the poppet....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3313_zpsf10e0960.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3313_zpsf10e0960.jpg.html)
This last photo shows the most restricted point on the valve inlet and outlet.... On the inlet side, the hole is the same diameter as the inside of the valve spring, and the area is twice as large as the transfer and barrel port.... If you look at the exhaust port compared to a stock Disco valve you will see a huge difference.... When you run a 3/16" mill in at a 20* angle, where it meets the transfer port flat it no longer apprears round, but is elongated fore and aft because of the angle.... To make that port round, I move the mill sideways 0.007" each way, which rounds out the hole at the transfer port, and enlarges it slighty in area.... (When I do this in .22 cal using a 5/32" mill, I get an equivalent diameter of 0.162", which matches the porting in a .22 cal).... In this case, the resulting port is 0.188" x 0.202", which is the equivalent of a 0.195" hole.... Not only is the area 78% larger, the 20* angle of the port and the rounded lower edge (cleaned up with a Dremel) must at least double the flow at the same pressure.... I'm very pleased with the results, and while these mods are not of the simple "home brew" variety, Sean should have no difficulty in replicating them on a production basis.... I'm about ready to install the valve and the Disco Double tube kit and test for leaks....
Bob
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very nice bob, this is def the route i want to take for disco when i double tube it. i think the bnm breech as enough meat to handle that big of a transfer port but not entirely sure..
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Thanks for the info rsterne.
I might order the one from Mcmaster. The only part that I'm not sure about is if has the correct threading.
I have being working on tuning by disco .22. i got it where i want it to be. I keep thinking about a double tube.
I did some valve work. I actually did not end up using it because it uses to much air. I might put this valve on if I every go double tube on it. Can't decide if I should spend more money on the disco or get another toy.
(http://farm9.staticflickr.com/8248/8624946239_2c7088618c_b.jpg)
(http://farm9.staticflickr.com/8401/8624953441_4718ed23c5_b.jpg)
It it ported but the tport opening is still stock size.
(http://farm9.staticflickr.com/8379/8626056290_37f0096822_b.jpg)
Here is how my disco is shooting. Mods: valve porting (not as much as the one in the picts), Home made PA and spring guide, Brass trigger, 3 screw trigger mod but only use 2
This is my latest shot string. I have set at that power so I get 15 shots.
(http://farm9.staticflickr.com/8539/8686791618_012789909a_b.jpg)
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I wouldn't say that's using too much air at that power level.... pretty typical for a Disco set up for 28 FPE....
Got the valve installed and the Disco Double tube kit assembled and trial fitted to the stock.... Norm did a beautiful job with the inletting, it just dropped right in....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3315_zps99476086.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3315_zps99476086.jpg.html)
It seems to be holding pressure just fine.... I made a band to hold the two tubes lined up securely and installed it just in front of the stock.... Once I'm all finished the development process I'll strip it all apart and blue the second tube.... Normally Lloyd supplies them finished, but I requested it in natural.... Next week I hope to get started on the breech....
Bob
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I wouldn't say that's using too much air at that power level.... pretty typical for a Disco set up for 28 FPE....
I have it tuned to 28Fpe and 15 shots with a different valve.
The in the picture valve at the same power level was giving about 32 fpe and about 10 shots and my larger Ext Dev.
That is looking sweat!!!!
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You will likely find that the larger valve could be tuned to use LESS air at any given FPE level and pressure, at least that is my experience.... Can it flow more air?.... YES!.... Can it make more power?.... YES!.... Can it do both together?.... YES AGAIN!.... Is it the answer if you want less power and more shots?.... MAYBE NOT!.... but it can probably be made to give you both by simply restricting the transfer port ONLY.... Having said that, it IS possible to go too large.... which is why I'm not going all out on this setup.... We have a very specific goal in mind, to get into the low-mid 900's with the new .30 cal JSB 46-50 gr. pellets.... Diablo pellets don't tend to work well over about 950 fps, so tuning the gun for over 100 FPE, while it might be kewl, could also be counter-productive.... It's going to be all about a balance between power and shot count....
Bob
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Those Gauges from McMaster-Carr are probably not much better than the Chinese gauges. In fact, they may just be another version. They are described as a 5% accuracy range. I've used them and you can expect a deviation of 150psi in some cases. Is what it is for that size of gauge in that price range.
Bill
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At least they might hold together.... I've had two of the Chinese gauges fall apart.... lens fall out, needle move around 1000 psi.... JUNK !!!
They either fail almost right away or seem to work just fine....
Bob
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WOW! I have never had that issue at all with the seven or so that I have used or ordered for others. In fact, all of them are still in service and working the same as they did when they were purchased. You'd think after the theft of so much intellectual property and product design, the Chinese would at least dedicate more resource to quality. after all, they have nothing invested in r&d.
Bill
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That is cool project once you can work out the details...
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Here is a photo of the roughed out breech.... all the longitudinal machining is done and it's bored 1/2" end to end.... This basically took me all day....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3321_zpsa731c751.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3321_zpsa731c751.jpg.html)
Lots of work yet to finish it; loading port, bolt slot, cocking slot, transfer port, and all the mounting holes including the slot for the front band....
Bob
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bob is this stuff going to be for sale as a kot ? or just the barrels ?
i want to do this to my disco, but i see the only thing holding me back is well money on hand right now and valve work but i def want start getting the ducks in a row for this
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On the initial order, I think Sean is planning on selling a few blank barrels to help defray the cost of the mandrel (which is now made!).... That will be for those who can do all the machining on the barrel themselves.... In addition, he will be supplying .30 cal barrels (0.300", for the JSB 46 & 50 gr. pellets) to fit the MRod (slide into an existing gun), which will also fit a BNM 1/2" ID breech.... When I have my rifle working the way I want, then he will be making repeating breeches (to fit the Disco/22XX), machining .25 and .30 cal barrels, and modding valves (and supplying hammers and springs if needed) to duplicate my gun as a kit, in both .25 and .30 cal.... That's the plan, anyway....
Bob
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that works for me man, gives me sometime to cover funding. gotta get 2 stocks and 2 double tube kits paid for before i can continue any other plans.
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Update on these barrels.... The mandrel is made, and the barrels will be produced to the following specs:
.30 cal Airgun barrel intended for the new JSB 46 & 50 gr. pellets
Made from CrMoly steel, hammer forged
Groove 0.300"
Land 0.294"
Twist 1 turn in 26"
6 Lands
OD 0.500" (0.590" also available)
Standard length 25" (12.5" for pistols)
What they are NOT: They are not intended to use 0.308" cast bullets, nor are they intended to use any bullet over 0.48" in length, as those will not fit into a modified .25 cal MRod magazine, and may not stabilize in the 26" twist....
Sean will be placing an initial order as soon as we can collect pre-orders and determine a price.... For THIS ORDER ONLY, and only for BARREL BLANKS with no machining, we will accept orders for lengths other than the above, but be advised there may be a small surcharge from the manufacturer for barrels over 29" long....
I will be contacting those who have expressed an interest in pre-ordering barrel blanks.... Anyone else who wants to get in on this initial order, either for blanks or for machined barrels.... please contact me ASAP.... Sean will be finalizing the list within a week, getting prices, and then contacting you to arrange payment.... Sean will be offering all machining services (chambering, porting, and crowning, and can even add a choke) at extra cost if you desire, please ask him for details directly....
Bob
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Should be a decent Coyote gun, and should anchor 'Chucks instead of them making their burrows as often happens with a .25 cal and almost always with a .22, it seems.... The range will be determined, as always, by the accuracy.... I don't have a BC on the new JSB .30 cals, but they are basically a scaled up King plus a bit, so the SD and BC should be about 27% higher.... in the 0.043 - 0.045 range.... 88 FPE at the muzzle would end up about 50 FPE at 100 yards, so you're talking decent .25 cal power at the muzzle, but at 100 yards instead.... Sighted at 50 yd. the drop at 100 should be about a foot....
I have not lost a Woodchuck for the last 7 years since I started shooting them in the brain , with any caliber. I have taken them with 14fpe Diana 34 .177, 350 .22 Springers, and Condor .22 & .25, all with a single shot to the head. None made it to the burrow out of 160 Chucks or so. 1 or 2 made it down just a little, but I was able to pull them out.
88fpe will not be enough to kill a Chuck with a vitals shot, but not sure if you intend to go for a head shot or vitals at 50 or 100yds. Those critters need a head shot unless you are using a .45cal airgun or a Win.30-30 or other Centerfire PB. They are really tough (I am sure you know that). I wouldn't even shoot them in the vitals with my 90-110fpe Condor .25 (depending on the pellet or slug).
Then again I prefer to keep my shots inside 40yds for Woodchucks/Groundhogs so as to maximize accuracy and shot placement.
Harry
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The 'Chucks I shoot here are Rockchucks, aka Yellow Bellied Marmots.... I always use headshots, but they are often on piles of logs or rocks, and with a .22 cal, even with a good solid hit at 30-50 yards, I recover very few.... With a .25 cal, I have a lot more success with them not disappearing down between the logs and rocks.... Maybe I need to study their anatomy a bit better.... perhaps I'm not hitting them in the right part of the head to "turn off the switch"....
Bob
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Can't wait Bob. Sounds like a fun shooter.
Joe
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hey Bob,
You mention availability of a choke...I am curious about possibility of getting one w/o and then perhaps getting it choked after some testing? Beyond that, how nessessary do you thnk it will be for top results/
cheers,
Douglas
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Choking barrels is one of Sean's speciaties.... He rolls them in with a huge converted pipe cutter with rollers instead of a cutter (or can lap them in).... There is certainly no reason you couldn't have it done after initial testing, other than it might mess up any bluing of course.... I've never had an existing barrel choked, so I can't comment on the change in accuracy, but it's certainly supposed to help.... I may get one of the two barrels I have coming choked to compare.... Here is his website, barrels are his specialty....
http://ramachining.blogspot.ca/ (http://ramachining.blogspot.ca/)
Bob
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I was able to get back to machining the breech today, and finished everything except the bolt slot.... The breech accepts a .25 MRod self-indexing magazine, and Lloyd at AirGunLab is tooling up to supply them in a 7-shot .30 cal version.... The breech accepts a 1/2" OD barrel, and the plan is for Sean to supply them in both .25 cal and .30 cal versions.... The boss on the front is 3/4" diameter, to accept a 7/8" OD Carbon Fibre barrel shroud, allowing the barrel to be tensioned by the screw-on Hatsan style air stripper.... Here is what it looks like at the present time....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3323_zpsdd2e25af.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3323_zpsdd2e25af.jpg.html)
The breech mounts in three places, at the rear to the RVA (end plug), in the middle to one of the two positions of the 4-48 screw (allowing it to be used on a Disco or 22XX tube), and at the front with a band around the main tube between the trigger and gauge location.... The barrel is solidly mounted with three 8-32 setscrews.... The rigidity of this breech and barrel assembly should be superior to any other breech I have seen on a Disco/22XX, eliminating accuracy robbing flexing and bending....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3325_zpsf4fc3cc6.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3325_zpsf4fc3cc6.jpg.html)
There are three holes in the middle of this breech because the holes drilled in the Disco tube I have were misaligned, so I had to drill and tap another hole in between them and use that.... Only that hole is counterbored in this breech.... Normally that hole would be absent, and both the other locations would be counterbored.... One difference in this breech is that I left enough material under the magazine to allow a standard 4-48 SHCS to be used instead of the custom low-profile one Crosman uses that accepts that tiny 0.050" allen key.... The thicker head on a standard 4-48 SHCS accepts a 3/32" allen key, so no more stripping out the head of the screw.... The 4-40 screws in the breech band will accept the same size tool....
I have passed along the names of everyone who has asked for a barrel from the initial production run to Sean.... He's pretty busy right now, but will contact all of you with a price as soon as he can.... In the meantime, I'll continue building parts so that when my barrel arrives hopefully it will the the last thing that needs machining....
Bob
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Awesome work as usual Bob. Cannot wait to see how this project turns out. As many know I am a huge fan of the .30 caliber.
Dave
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Over the last couple of days I made the two bolts (.25 and .30 cal), the bolt handle, and machined the bolt slot in the breech.... The bolt design is quite unique, thanks to Sean.... at least I have never seen it before.... It is probeless.... The sealing O-ring is in a groove in the end of the barrel and the bolt slides through it....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3379_zps01c83a78.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3379_zps01c83a78.jpg.html)
Rather than have either a hollow probe (which loads the pellet by pushing on the base, and the air flows through it).... or a thin extended probe (which loads the pellet by pushing inside the skirt and the air flows around it).... this bolt simply has a flat end.... The key is in the bolt slot.... The bolt pushes on the base of the pellet (or bullet) to load it, and stops with the base or skirt past the barrel port.... It is then withdrawn to clear the barrel port completely, leaving no obstruction to the airflow once in the firing position....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3374_zps3c8b6a88.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3374_zps3c8b6a88.jpg.html)
Sean's original bolt slot design was "T" shaped, the bolt moved past the battery position, was withdrawn and turned down to lock.... We then modified it to a triangular shape, where the bolt handle was pulled down and back on an angle to the locking position.... I then saw a photo of the Crosman Rogue which has a slot shaped like the one in the above photo, and uses the retraction of the bolt to the firing position as a safety interlock (as I understand it).... I adopted that rectangular slot design and Sean's probeless bolt for this rifle.... In addition to having no obstruction to the airflow in the barrel, the bolt handle, once in the firing position, can't pop up on firing.... The bolt in the second photo is shown in the firing position....
Bob
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Looks good Bob. After bending my original BNM handle from cocking at near coil bind with the .047" spring seeing that thin bolt handle makes me wonder if it will bend on you too if used with high tension. I'm guessing you planned ahead for that and made it from high strength steel?
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It's a 10-32 high tensile SHCS, and set into a recess in the bolt so it's full diameter at the edge of the bolt where the leverage is.... It's a full 3/16" diameter....
Bob
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Rather than have either a hollow probe (which loads the pellet by pushing on the base, and the air flows through it).... or a thin extended probe (which loads the pellet by pushing inside the skirt and the air flows around it).... this bolt simply has a flat end.... The key is in the bolt slot.... The bolt pushes on the base of the pellet (or bullet) to load it, and stops with the base or skirt past the barrel port.... It is then withdrawn to clear the barrel port completely, leaving no obstruction to the airflow once in the firing position....
That is an excellent idea. And so obvious.
Jerry
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I haven't had much time lately to browse the forums but I try to keep up with this project as much as possible. Great progress and I enjoy the inovation in this project. I really like the probless bolt and the J slot. I'm looking forward to your results from the finished project.
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I got most of the remaining parts made today.... Here is the front breech mounting band, shown installed on the breech....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3382_zps89461c90.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3382_zps89461c90.jpg.html)
It fits over the tube between the trigger and the gauge, and securely clamps the front of the breech to the main tube.... I then made a new hammer and RVA assembly....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3384_zps4c64ee1f.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3384_zps4c64ee1f.jpg.html)
The hammer is the same length as a Disco / 22XX hammer, but it is cylindrical and will therefore work with a Disco, MRod, or PRod trigger group.... If an MRod trigger is used, it should be shimmed down 0.030" because it is designed for a thicker main tube.... The hammer is drilled to accept a QB 7X hammer spring, which is longer and larger in diameter, stiffer, and has more travel.... The cocking pin is moved back 0.065", allowing slightly more total hammer travel.... The hammer weighs 58 gr. the same as a Disco hammer, and has a notch to clear the rear breech screw location used on a Disco.... The spring guide is made from a piece of 7/32" drill rod with a nut threaded on, peened, and turned.... It is long enough to protrude through the RVA adjusting screw and serve as a cocking indicator.... It weighs 15 gr., so the total hammer weight with guide is 73 gr., 26% heavier than a Disco hammer....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3388_zps79491a46.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3388_zps79491a46.jpg.html)
You will notice that the hammer face is counterbored 0.070" to increase the hammer stroke and limit the valve lift.... In combination with the 0.070" shortened valve stem, the stroke has increased from 0.58" to 0.72" (an increase of 24%), and there is still 0.18" of valve lift available.... I have found that to be more lift than required on all other Disco platforms I have worked on, in fact it is seldom more than 0.12" in a properly tuned gun.... The RVA is made from aluminum, and carries an adjusting screw made from a 3/8"-24 NF bolt.... The spring and guide can be removed through the threaded hole, no need to remove the end plug once installed.... The guide slides easily through the adjusting screw, and protrudes when the gun is cocked, giving a visible cocking indicator.... There are two flats on the adjuster to allow it to be turned with a 5/16" wrench.... and it is locked in place with a thin (jam) nut once adjusted.... I have enough travel on the RVA to go from no preload to coil bind, about 16 turns....
I am now at the point where I can install the breech on the main tube and inlet the stock for the front breech band.... Once that is done, I can get on with sanding and finishing the stock.... Most of the gun should be done by the time the barrels show up....
Bob
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Sweet idea with the band. Why no band on the rear too? On mine the rear is what came loose after the hard cocking. It could be made to screw into the sides of the breech since it couldn't be mounted underneath like the front band is.
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Why would you need a band on the rear, it bolts into the rear plug / RVA with an 8-32 screw.... I have never had a problem with that (even in aluminum RVAs), and some of the hammer springs I have used required over 20 lbs. to cock them.... Mounting a 6" long breech with 2 screws, one at the back and one (tiny one) in the middle, has always seemed a bit foolish to me, however....
I usually figure if it ain't broke, it don't need fixin'....
Bob
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My rear breech screw stripped the tube from the cocking pressure with the .047" spring near coil bind where the breech was lifting up and causing misalignment with the internals where cocking became hard to do and sometimes would not cock at all, and that was after Lloyd bored the tube to change from the tiny screw to a larger one. The larger one from him held it's place. Maybe I needed the tube bored for a larger rear screw to better handle the extra forces.
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Bob - Do you have a pressure relief hole, in the air tube, right behind the valve? Either that or some flats milled on the side of the hammer would relieve the pressure built up from hammer travel. I had this problem on one of my guns and I think I recall reading about this happening on one of your past builds too.
Jerry
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The rear screw isn't tapped into the tube, it threads more than one diameter into the end plug, which is steel on a Disco unless it's been changed.... You could easily hang 500 lbs. on that screw.... I don't doubt you had a problem with it, but I'm guessing it was stripped on installation, not due to the cocking force.... Either that, or the middle screw broke first, and the leverage of reefing up on the breech with ONLY the rear screw in place tore it out.... In other words, the middle screw caused the problem, not the rear one....
I ground a notch in the rear bottom corner of the valve to vent the air between the hammer and the valve out through the hole that is just behind the bottom valve screw in the Disco tube.... exactly because of the problem you mention, Jerry....
Bob
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can you guys post a picture of the relief whole. I have my disco apart right now waiting for a part and it would be a perfect time to do so. Is it as simple as drilling a small hole on behind ( towards the hammer) the bottom valve screw.
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True about the plug hole Bob I should have been succinct about it like I was in another thread earlier. That makes sense and explains why it got worse over time with me cocking at high spring pressure. I think tapping a hole for a larger screw could solve it as long as the screw was not over tightened.
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can you guys post a picture of the relief whole. I have my disco apart right now waiting for a part and it would be a perfect time to do so. Is it as simple as drilling a small hole on behind ( towards the hammer) the bottom valve screw.
Here are a couple pics. In my case the valve was blocking the vent hole so it had to be notched out.
(http://imgnook.com/9BLVCo.jpg)
(http://imgnook.com/uF1Xlo.jpg)
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Thank you very much. I might move mine a little. The whole is bigger than what I experted.
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I installed the cocking pins in the bolts today and machined out the breech to clear them....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3408_zps20f71f19.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3408_zps20f71f19.jpg.html)
When the bolt is in the "down" position (shown), the head of the 4-40 SHCS rotates out of the way of the hammer pin into the recess milled in the side of the breech.... When the bolt rotates to the "up" position to open and load a pellet, it engages the hammer pin, drawing it back to cock the hammer.... Nothing magic, but complicated to measure umpteen ways to make sure it all works properly and allows the bolt to retract far enough to remove the magazine when the gun is cocked....
I inletted the stock for the breech band, finish sanded it, and put on the first coat of Watco Danish Oil yesterday.... The stock will be done in about a week.... I wet sand each of the next six coats, two with 220 grit, two with 400, and tha last two with 600.... and then give it a final coat of Minwax.... I think the "Forest Camo" combination of black, brown, and green in the Boyd's Laminated Blaster stock should be quite attractive when done.... It is much darker than the first photo with it unfinished....
I think all the machining is done except for the barrel.... and a shoulder on the Hatsan air stripper to locate the carbon fibre shroud.... and then the last step will be to make a transfer port from a piece of 5/16" Teflon rod.... Basically, once the barrel arrives, the gun is only days (hours?) away from initial testing.... I've already pulled the trigger and heard a satisfying BANG when the hammer opened the valve for the first time.... I won't be bluing the Disco Double tube and any small parts until after testing....
Bob
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Love that bolt design. I was working on a way to do the same thing, that is much simpler than what I cooked up.
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Very interesting project and nicely done ! I'm just a little curious as to using a .30 cal barrel with a 1/2" OD . Doesn't leave a very thick wall & could have flexing issues ? Please don't take offence, Just asking.
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Actually, it will be a lot stiffer than a Crosman barrel in .22 cal with a 7/16" OD.... and it happens to be the same size as my DAQ .308 Exlie.... I figure if it's good for 180 FPE that half that shouldn't be a problem....
HOWEVER.... the gun will have a 7/8" OD x 3/4" ID carbon fibre shroud in compression and the barrel in tension, the forces generated by a threaded on Hatsan style air stripper.... *grin*....
Bob
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Nice work Bob! That is just an awesome air gun. 8)
I really like that Stock too.I may just have to have norm put one on the truck for me real soon..;)
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While waiting for our new barrels to arrive, I thought I'd do a practice run using a .308 cal PB barrel I had.... I cut off the .300 Win. Mag. chamber, ending up with a 21" usable section, and then I turned down the breech end to 1/2" OD to fit into the breech, and machined in a chamber and leade and a transfer port and O-ring groove.... Here's how it turned out....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3413_zpse076ffb6.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3413_zpse076ffb6.jpg.html)
I assembled it into the breech to check the functioning of the bolt, and the nose pushes a pellet just past the transfer port and then withdraws into the "J" slot so that it is just clear of the port and completely out of the airflow, just as designed.... I also machined out the groove in a .25 cal MRod single shot tray to take the .30 cal pellet.... It clips onto the end of the barrel which protrudes 0.060" into the magazine bay, the same way the magazine mounts....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3410_zpsb3feda6b.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3410_zpsb3feda6b.jpg.html)
By adjusting the diameter of the O-ring groove inside the barrel, you can customize how tight the O-ring grips the nose of the bolt.... I have set it up for a noticable drag, but the pellet slides through fine.... I'm sure it will seal perfectly as I've done this type of breech seal in the past with great results.... While outside the original design parameters of the gun, this barrel and loading tray will allow me to test cast .308" bullets up to 120 gr. in single shot mode (providing I cut the chamber deeper), just to satisfy my curiousity....
Bob
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Just a couple of pics of the finished stock.... I'm very pleased with the results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3414_zpsbe99f64e.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3414_zpsbe99f64e.jpg.html)
It's a Boyd's Blaster in Forest Camo (green, brown, black).... Inletting done by Norm at Discos-R-Us....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3417_zps7c653527.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3417_zps7c653527.jpg.html)
I finished it with 7 coats of Watco Danish Oil, wet sanded (2 x 220, 2 x 400, 2 x 600) and then a final coat of Minwax....
Bob
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cComing along very nicely! I just got the Boyd stock stuck but in nutmeg but I just finished with Minwax wipe on poly satin. I'm loving it but I have not been to shoot with it yet. Long story shot, I was porting the disco gauge port. Messed it up. Now I'm waiting from crosman to deliver. Lesson learned....get the right tool for the Job....Buy a press drill.
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The easy way for a Disco gauge port is to buy the one from a PRod and use a 1/8" male-female NPT adapter (make sure it has a sufficient pressure rating) to mount the gauge.... It has a huge through hole....
Bob
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Thanks Bob.
I ordered the Prod gauge port from crosman and the adapter from McMaster. I ordered this one http://www.mcmaster.com/#catalog/119/41/=mtjhi0. (http://www.mcmaster.com/#catalog/119/41/=mtjhi0.)
I was looking for better gauge than the disco but it has been very hard to find. I found this one but I have not been able to find anyone that sells it online.
http://www.winters.com/index.php?option=com_content&task=view&id=243&Itemid=252 (http://www.winters.com/index.php?option=com_content&task=view&id=243&Itemid=252)
The local distributer will only order $100 or more from winters.
I have been reading many of your post. Very good info. Thank you for posting all the info.
Here is a pict of the disco waiting for the port.
(http://farm8.staticflickr.com/7288/8740086998_60ac86f0cd_z.jpg)
Daniel
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Part# PSP103000 looks like what you want if you have the strong valve screws, PSP102000 would be for the 2k psi gauge for the stock disco guys.
I can't find them sold anywhere else but winters. You don't have another distributor to choose from fairly close by? If not then you could always buy 3 gauges to get the order sent to you then sell the others to people on here if you didn't want to keep a spare.
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Part# PSP103000 looks like what you want if you have the strong valve screws, PSP102000 would be for the 2k psi gauge for the stock disco guys.
I can't find them sold anywhere else but winters. You don't have another distributor to choose from fairly close by? If not then you could always buy 3 gauges to get the order sent to you then sell the others to people on here if you didn't want to keep a spare.
If I get on I would get the 3000psi one. I usually fill to 2100 and sometimes to 2250 but not more than that. I did replace the screws with SS ones that which have just a tad bigger head. It helps centering the T.Port. I would love to upgrade my valve screws to larger ones but I don't have the tools to do it. If I did I would be filling up to 2500 psi and tune for higher pressure.
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Ask Norm or Lloyd for the strong screws as they may have them. All it takes to swap the old ones out with the new ones is a set of Allen wrenches which is not expensive.
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McMaster Carr sell a 4000 psi mini-gauge with 200 psi increments.... I have some and they look great (haven't tried one yet)....
I have never seen any "strong screws" that are 8-32 thread with a 5/16" head to upgrade the Disco valve mounting.... 10-32, which require redrilling and tapping the valve.... and 8-32 with a smaller head that doesn't fit the 5/16" hole.... but nothing suitable as a "screw in" replacement for the pan head screws that Crosman supplies.... Is this something new, and if so, why hasn't there been a big announcement on the GTA as it's an IMPORTANT bit of news.... I'll take a dozen sets right now!....
Bob
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I just email lloyd and PM norm. I'll find out soon. I will post here if they have them. I have one of the McMaster 4000 psi gauge but I was hoping for a 3000 so I can get increaments of 100.
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increaments of 100.
Unless you get a gauge with more degrees of swing, the only difference (between a 3000 psi guage with 100 or 200 psi increments) is you won't have to guess a "half increment".... The number of degrees swing for 100 psi will be the same.... I have some 3000 psi Chinese gauges (junk) that are 200 psi increments, and they are plently easy enough to read to 100 psi.... when they work....
Bob
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I have never seen any "strong screws" that are 8-32 thread with a 5/16" head to upgrade the Disco valve mounting.... 10-32, which require redrilling and tapping the valve....
Doh that's right Bob. Completely forgot about that.
You could ask Norm if he could do that work for you rd. Lloyd is too busy right now so I don't know if he would be able to.
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I will eventually get it done. My disco has been down for 3 week now. I need to do some shooting and make sure the latest valve changes did any good. I opened the throat a little more, increase the size of the valve port, reduced the OD of the valve stem to allow for more flow and made a long probe bolt. The transfer port is still stock size. Right now I'm trying to make the disco a little more efficient between 25 and 30 fpe. I'm getting 15 shots at 28 fpe from 2100 to 1500 psi.
I will give the mcmaster gauge (0-4000) a try.
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I would be surprised if you gain any advantage by opening out the throat and slimming the stem, or opening the valve exhaust port, if you are using a stock 0.140" transfer port.... The barrel port (0.134") is the smallest restriction, followed by the transfer port, and everything else is already bigger on a stock Disco....
Bob
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Bob, I'm not necessarily looking to get more power out of the disco. I'm looking for better air flow which should improve efficiency. I'm keeping the T.port and the barrel port stock because I'm using it so it can regulate itself. It gives me a very flat curve at least form 2100 psi to 1500 psi.
So far every adjustment, I gain a few FPS (10 to 25) on the same about of air. I know at some point this will stop. I'm not power hungry but looking for consistency in the shot string. I think I have reached that point but I figure I would try. Worse comes to worse I put the stock stem back on and the opening of the through should not have affected anything.
If I decide to go for more power the first thing I have to do is open the barrel port.
Daniel
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ahhhhhhhh.... I know where you're coming from.... I often do the same thing, but in a different order.... I build the gun to be an efficient powerhouse, and then fit a restricted transfer port to drop the power, flatten the curve, and increase the shot count.... Yes, it works very well....
Bob
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I'm new to the AG world so I'm learning as I go with lots to be learned. I do as much research and ask before I make changes. On thing I wish I had are better tools. I only have a drill with high quality drill bits, a dremel tool and so machining files and dies that use to belong to my wife's grandfather. This makes it hard to make mods to the valve or build parts. I do have patience which helps.
My disco is shooting at 820-835 with 18.1 jsb's. I make shot faster but it seam that is the sweat spot with the current tport configuration.
I find your posts extremely helpful and the work you are doing in outstanding. I wish I had the skills to do the same.
Note: I talked to Norm and I will have to get the valve rethreaded for the larger screws. I think I'm going to hold on all that until I do more testing on the current set up. I also have an assortment of hammer springs to test out.
Daniel
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I personally recommend not using a .047" spring and just top out with a .041" spring since the largest one contributed to cocking issues and part problems in my disco. Several shipments across the country to fix the reoccurring problems add up in cost quick. I have well over $1k in my disco partly because of it such as a replacement breech, bolt handle and cocking screw from all the pressure of cocking with that heavy spring. There shouldn't be any damage developing from using the .041" spring if you're not rough with the cocking.
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I use a 0.040" wire spring in Discos, although I have on occasion gone to 0.042".... If I need more than that, I increase the hammer travel and weight and go to the hammer spring from a QB78, which is 0.047" wire but it is 1/2" longer and so the spring rate isn't that much higher.... You get the extra hammer energy and momentum from the extra travel and weight instead of a mondo, hard to cock spring.... That's what I'm using in this .30 cal build....
Bob
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I have the heave sprint from discosrus which by my measurements it is about .039 wire. I have that one in two lengths. The regular length and a shorter version. I have found that the shorter length gives me more consistent number or I should say my standard deviation is smaller.
The next spring I'm going to try is .042. That is what I have have. I have other springs heavier than that by I discovered the same thing that sqlr kir mentioned. I was trying to use slightly heavier spring to reduce the preload. I don't know if that would help or not.
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Update on the screws: Lloyd does have the valve Screws size 8-32. I'm getting some to test out. So I might be filling to 2500 psi after all
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Lloyd confirmed his 8-32 screws are stronger than the ones in that size that you currently have rd?
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This is what he wrote to me:
Hi Daniel,
Yes I do. If you go to buy them, they go by the name of: Low profile socket head cap screws, high strength alloy steel. The direct replacement size is 8-32 x 3/16 long. The problem is that the shortest I can find them in is 1/4" long, so I have to grind off 1/16". I will send you some for a few dollars if you can grind them off your self.
You live in Richmond, right? Maybe you can find some 3/16" long ones at an industrial supplier, and if you can, would you let me know?
I've attached a pic of some of the screws installed in a valve.
Lloyd
I don't know if they are rated for 3000 psi. I'm only looking to go up to 2500 psi
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Daniel.... Would it be possible for you to post the pic Lloyd sent you?.... If you right click on it, select Properties, you can find the URL where the photo is.... then copy/paste it here....
At 3000 psi, with three 8-32 screws, anything higher than 120,000 psi tensile strength will have a 2:1 safety margin or better.... At 180,000 psi (which is common for high tensile SHCSs) the safety margin in shear would be 3:1 at 3000 psi.... As long as the head diameter is 5/16" to fit properly in the holes in the Disco tube, you should be good to go....
Bob
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here is the picture from lloyd!
(http://farm3.staticflickr.com/2862/8757489567_d4bd86621d_b.jpg)
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I looked on loyds site but cant find the button head screws listed to buy???
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^X2....
I've both PM'd him and emailed.... He's building a house right now, so very busy....
Bob
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I got a response from Lloyd RE the high tensile 8-32 screws he has.... They do NOT have a 5/16" head, it is the standard 0.270" diameter available from several suppliers.... Because of the high tensile strength, they have plenty of shear strength, but the smaller head diameter, when used in a Disco tube, will move the valve back 0.020", causing a small misalignment of the transfer port.... If you are enlarging the port, and allow for that, in itself that is not an issue.... I do have a concern about the poor fit in the hole, however.... Instead of the entire rear half of the screw head spreading the load into the tube wall, the bearing area is drastically reduced.... in fact it starts out as a point contact.... I have seen a very slight "settling in" of the screw head into the rear side of the hole in the tube when using 10-32 screws (which do have a 5/16" head) at 3000 psi in a Disco tube.... This is not a safety issue, it just indicates that the load on the screws is so great that it is exceeding the local yield strength of the tube until the valve moves back a few thou and all three screws take up equal load.... This is predicted by the strength formulas because of the relatively thin wall (0.065") of the Disco tube.... My concern with using screws with smaller heads is that they may have a tendency to move back even further until the ability of the tubing wall to resist the force equals the load.... The screw would have to move back an additional 0.020" before the contact width was 0.250".... which is still 25% less than the width of the stock 5/16" screw head.... It wouldn't surprise me to see that happen at 3000 psi....
Is this a safety concern?.... I'm not sure.... If the deformation stops at that point, it's only an inconvenience, albeit one that has to be allowed for by moving the transfer port forward in the valve by the same amount so it still lines up with the hole in the tube and breech.... However, I would be a LOT happier if the head diameter was the full 5/16" like on the stock pan head screws, or on the 10-32 screws.... I have used those 8-32 low profile SHCSs in a redrilled 2260 tube, and they worked fine.... However, the holes in the tube were also 0.270", so they provided a full cradle for the head of the screw.... I have every confidence in using them in that way....
Bob
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Bob,
I went ahead and ordered the screws anyway. I'm going to try to shim them with a saw blade piece. The metal is ver hard and just by change the thickness is .022. I only need to shim the back of the screw which make it easy.
This will allow the bolt and shim to make full contact with the tube hole. I'm attaching a picture to illustrate.
(http://farm9.staticflickr.com/8552/8760568050_bc38c775d0_b.jpg)
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I got a response from Lloyd RE the high tensile 8-32 screws he has.... They do NOT have a 5/16" head, it is the standard 0.270" diameter available from several suppliers.... Because of the high tensile strength, they have plenty of shear strength, but the smaller head diameter, when used in a Disco tube, will move the valve back 0.020", causing a small misalignment of the transfer port.... If you are enlarging the port, and allow for that, in itself that is not an issue.... I do have a concern about the poor fit in the hole, however.... Instead of the entire rear half of the screw head spreading the load into the tube wall, the bearing area is drastically reduced.... in fact it starts out as a point contact.... I have seen a very slight "settling in" of the screw head into the rear side of the hole in the tube when using 10-32 screws (which do have a 5/16" head) at 3000 psi in a Disco tube.... This is not a safety issue, it just indicates that the load on the screws is so great that it is exceeding the local yield strength of the tube until the valve moves back a few thou and all three screws take up equal load.... This is predicted by the strength formulas because of the relatively thin wall (0.065") of the Disco tube.... My concern with using screws with smaller heads is that they may have a tendency to move back even further until the ability of the tubing wall to resist the force equals the load.... The screw would have to move back an additional 0.020" before the contact width was 0.250".... which is still 25% less than the width of the stock 5/16" screw head.... It wouldn't surprise me to see that happen at 3000 psi....
Is this a safety concern?.... I'm not sure.... If the deformation stops at that point, it's only an inconvenience, albeit one that has to be allowed for by moving the transfer port forward in the valve by the same amount so it still lines up with the hole in the tube and breech.... However, I would be a LOT happier if the head diameter was the full 5/16" like on the stock pan head screws, or on the 10-32 screws.... I have used those 8-32 low profile SHCSs in a redrilled 2260 tube, and they worked fine.... However, the holes in the tube were also 0.270", so they provided a full cradle for the head of the screw.... I have every confidence in using them in that way....
Bob
Yes, a slight misunderstanding here. I have used both the 8-32 (.270 head dia) and the 10-32 (.312 head dia) low profile socket head screws and of course the 10-32, with full contact will always be the preferred choice. Using the 8-32 screws will indeed allow the valve to seat .020 farther back in the tube, with a corresponding misalignment of the transfer port, which for many applications is not an issue.
I do want to clarify, that with the smaller head size, when loading the valve with air pressure in the tank, a 2000 psi fill will deform the rear semi-circular portion of the hole in the tube less than .001". Filled to 3,000 psi, the deformation will still be less than .002". This is assuming the 70ksi compressive strength of the tube material, and not adding in any benefits from strain hardening.
So you have the .020 shift for the head size, and an additional .001-.002 for the heads to seat into the tube material. Actually, the manufacturing tolerances in the tube holes and the valve holes exceed that .002, so any distortion observed will be as much from the manufacturing tolerances as it is from the screws.
One very good indicator that I have found that the screws in a disco have been overloaded or have passed their useful life is when unscrewing them from the gun. If any eccentricity can be felt..... tight-loose-tight-loose... as you unscrew the screw, you know it has been bent.
So that I am not misunderstood, when going to the high strength alloy steel Low Profile SHCS, tapping the valve out to 10-32 is the first choice. Using the 8-32 high strength alloy steel Low profile SHCS is still better than stock, but it does present different circumstances that must be fully understood.
I hope that helps.
Lloyd
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I understand the concept.... but do you understand the forces involved?.... At 3000 psi, there is over 1300 lbs. force on the valve trying to push it backwards.... How fast do you think one of those shims might travel if it decided to fly out under the pressure of over 400 lbs. pushing on it?.... close to supersonic comes to mind!.... Worse yet, then you only have 2 screws taking the load.... and if another shim gets forced out, then only one.... Suddenly your 3:1 safety margin has disappeared because only one screw is now taking the 1300 lbs. of load.... Will it fail and shear off, leaving you with only two?.... Maybe, maybe not.... If it does, when the valve suddenly moves back 0.020" will another screw fail from the impact?....
I'm sure you get my point.... No way in he!! would I even consider doing that....
Bob
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Bob,
Very good point. I think I will stay away from that. I'm just going to get a second valve taped for 10-32. Then I will have both options. I got the prod gauge port on the mail today. What a difference in quality? I installed the McMaster 0-4000 gauge to try it out. I'll gas it up tonight for a pressure test.
Daniel
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HI Lloyd, thanks for chiming in.... much appreciated.... I used 1010 mild steel with a 44K yield in my calculations, and with three screws all taking equal load, I get a 0.150" contact width per screw required at yield at 3000 psi.... in other words, if the yield strength is 44K, with 3 screws, they in theory should "settle in" and stop moving after that.... Using a 0.312" hole and a 0.270" head, that means the screw has to move 0.004" aft.... for a total of 0.025".... This is assuming, of course, that all the holes in the valve and the tube are drilled in EXACTLY the same plane, which is VERY unlikely.... I didn't duplicate the calculations using 70K for the compressive strength of the tube because I don't know what material it is.... but CrMoly is only 63K yield IIRC?....
Anyway, I overestimated how far the valve is likely to move back, but since I've seen a fractional settling in even with a 5/16" head size on the 10-32 screws at 3000 psi (I thought you had as well?).... I think we can assume that the valve might, on average, end up about 0.025" further back than it should.... but we can also assume that once it has settled into it's new position it should be perfectly safe.... wouldn't you agree?.... Sorry if I first erred on the side of caution....
Bob
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Rdsail.... Yes, the PRod gauge port is a lot bigger thru hole, but it uses 1/8" NPT threads so does not accept the Disco gauge adapter which is straight thread sealed with an O-ring....
On reflection, I don't think there is any problem running the 0.270" OD head size on the high tensile screws.... but I would move the center of the valve exhaust port forward about 0.025" to allow for the difference in diameter and any "settling in" with the smaller screws....
Bob
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bob,
I air up the disco and the McMaster gauge seams to be reading 100 psi lower than actual. The only thing I wish it was different for the needle to be pointer. I'll let it site over night and see if there are any leaks. I filled to 2200 psi for the pressure test. I can't wait to test it tomorrow.
Lloyd,
thank you for all the help!
Daniel
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I got the gun assembled with the short .308 PB barrel and fired a few test shots tonight.... First the photo.... I know, it's ugly with the barrel shorter than the tubes.... and parts still needing bluing.... but you can see the potential there....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3422_zps343d778e.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3422_zps343d778e.jpg.html)
The gun was pretty hard to cock, I'll have to take a look to see if there is anything binding.... However, I was still able to cock it at coil bind, and the good news is that is way too much preload, even at 3000 psi.... The first shot was the fastest, the gun was very loud, and the 46 gr. JSB pellet screamed through the Chrony at 971 fps which is 96.3 FPE.... Four shots later it was down to 920 and those 4 shots used 700 psi.... I backed the adjuster out 2 turns, and got 6 shots starting at 953 and ending at 918, using 750 psi.... Out 2 more turns, and I was starting to get a string.... Starting at 2900 psi (my tank needs filling) I got 10 shots starting at 914, peaking at 929, and ending at 886, and it used 800 psi.... Backed out 2 more turns, starting at 2900, I got 13 shots starting at 861, peaking at 906, and ending at 860 fps at 2000 psi.... That string averaged 880 fps (79 FPE) at an efficiency of nearly 1.1 FPE/CI.... At 8 turns out the usuable pressure range is from about 2600 down to 1600, returning 14-16 shots in the mid 800s.... and at 10 turns, the string starts in the high 700s, peaks in the low 800s, and returns, but this is with running stock Disco pressures starting at 2000 psi and ending at about 1300.... and the gun is still shooting 65 FPE, three times what a stock Disco does....
These are just preliminary tests, using upsized JSB 46 gr. pellets in a 21" barrel.... I just couldn't stand the suspense of waiting until the new barrels get here.... The additional barrel length should add roughly 5 FPE.... but I have already surpassed my goal of 88 FPE in .30 cal.... so tonight's testing was a resounding success.... BTW, I was running a 3/16" transfer port, I can go to 7/32" if I want to....
Bob
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Great Job Bob!
It is amazing the numbers you are getting out of the disco. It is going to be nice once you get the barrel in and start shooting.
Daniel
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Bob,
I shot some strings. I did not record them but I gained about 50 fps on the same power setting as before. (4 turns from binding point) The only thing I noticed is that It shots are slow on pressures over 2050 psi, Significantly slower. The valve seams to close too fast over those pressures. My shot range in relation to psi went up before I could here the hammer bounce starting at 1450 psi now it starts at 1200. So it starts wasting air at a lower psi. My high before was of 848 now my high is 898. I might have to tune it down some. I gained about 2 shots over all taking into consideration that my PSI range went up. The deviation went up.
What this tells me is that I might not have to fill over 2000 psi after all. I'm going to try my short heavy spring (-2.5 coils). I alway got a better deviation with the shorter spring.
Any ideas on how to increase my speed over 2000 psi? Heavier hammer? I don't want a heavier spring because the cocking will get harder.
I was not shooting for accuracy right now but from 15 yards I'm getting a ragged hole. I was not trying to shoot well. Just looking at chrony for numbers.
Thanks.
Daniel
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Sweet. Congrats Bob.
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Daniel, it's a bit hard for me to keep track of what you are doing, so difficult to offer advice.... The details of your project get buried pages back in the info on my .30 cal (eg. I don't even know what caliber your gun is or the pellets you are shooting).... Perhaps it might be better to start your own thread, giving the details of what you have done with the results at each stage so that I can follow it easier?.... Generally, a heavier hammer and a stiffer spring or more preload all act in a similar manner.... Increasing any of them allow a higher pressure before the velocity drops off.... Increasing the pressure (providing you have enough hammer strike) will allow the gun to produce more power.... It's a matter of deciding "how much is enough" and what pressure range you want to (or can safely) run.... My .30 cal can be tuned in a variety of ways, with higher pressure producing more power, and likely fewer shots.... Once completed, I'll have to decide where I want to tune it.... I typically go for as much as I can get (within the safety limits of the platform) and then detune it for he results that make sense, balancing power vs. shot count, with an eye to reasonable efficiency.... which for me, means striving for over 1.0 FPE/CI....
Bob
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Bob,
sorry for highjacking your thread....I'll start a new one but I'll keep following this one. I'll leave with one note. My efficiency went form 1.06 to 1.42. I could not believe the numbers the only thing is that I don't get as a flat curve as I used to.
Thanks for the Help.
Daniel
Gauge note: the mcmaster gauge does not read as well as the disco one. 100 psi low. I'll put the old one back on on the next tear down.
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Nice work Bob. I love it when hard work pays off.
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Very inspiring 8). Now test it on a yote?? ::)
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Very nice Bob, and a good range of power levels to choose from.
Seeing that you ended up shooting at 6 to 10 turns out, I can see why it was hard to cock at coil bind, LOL.
A well thought out project!
Lloyd
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I changed the gun over to a rear cocker last night, and also enlarged the transfer port to 7/32".... Here is the hammer, which now weighs 82 gr. with the cocking knob....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3436_zpsd547d809.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3436_zpsd547d809.jpg.html)
The gun is now very easy to cock.... I put a small O-ring on the shaft which can be used to directly measure the valve lift.... You simply slide the O-ring up against the back of the RVA screw, cock the gun, fire it, and the O-ring slides back exactly the amount the valve opens and you can measure the space with calipers.... I did that for all RVA settings from coil bound to 12T out, for the first shot, and the last shot before the velocity fell more than 4% below the peak.... The smallest lift measured was just under 0.06", and the largest was 0.13".... In virtually every case where there was a proper bell-curve, the lift at the first shot was about 1/16".... and at the last shot was less than 1/8".... This is a very valuable piece of information, and while it won't be the same for every gun, for this gun it indicates that limiting the valve lift to 0.15" (eg. by having the hammer hit the back of the valve at that point) would not have any affect.... That means I can lengthen the hammer stroke on this gun to a full 3/4" by grinding a bit more off the valve stem or counterboring the front of the hammer a bit more.... The fact that the valve lift was virtually the same regardless of pressure and preload.... once the gun was adjusted for a proper bell-curve.... was a bit of a revelation to me.... though in retrospect it makes perfect sense....
The larger transfer port increased the power a bit, made the shot strings more curved (and hence shortened them), and required about 3 turns less preload on the RVA for the same FPE level.... Possibly 1 turn of that is likely due to the slight increase in hammer weight with the longer guide and the cocking knob.... Here are the results of the testing, from coil bind to 12 turns out, by which time the fill pressure required was less than 2000 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleShortBarrel_zps82907bb6.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleShortBarrel_zps82907bb6.jpg.html)
You can see that with a 3000 psi fill, anything within 6 turns of coil bound, while producing a bit more power, drastically shortens the shot string, and of course wastes a lot of air.... I saw 1000 fps (102 FPE) with everything maxed out at 3000 psi, however.... but the gun ws using nearly 200 psi per shot, and was down 4% in just 3 shots.... The best setting I could find was 7 turns out, starting from 2900 psi and ending at 1900.... It peaked at 929 fps (88 FPE), and averaged 913 fps (85 FPE) over 11 shots.... but the efficiency was only 0.88 FPE/CI.... This is the first gun I have tried where the area of the transfer and barrel ports (0.219"D) were larger than the area of the throat, which is the equvalent of a 0.203" hole.... I'm pretty sure that is why I couldn't get over 1.0 FPE/CI like I did with the 3/16" transfer port in the initial trials yesterday.... This leaves me with two choices, either drill the throat out to 1/4" (it is currently 15/64").... or refit the 3/16" transfer port.... The former should increase the power even further, and may increase the efficiency slightly.... The latter will drop the power a bit, but increase the shot count and efficiency.... I will wait until I get the new longer barrel to make the final decision.... but since I'm already pushing these pellets into the mid 900s more power may not be the answer.... so I'm leaning towards going back to the 3/16" transfer port with the 25" barrel....
Bob
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Very nice Bob. I like the look of the handle. Lloyd and I have talked about switching to a rear cocking knob on mine which I may decide to do in the future but I would also have to modify the breech to mount the scope more forward so it would not be blocking the knob making it hard to reach. Is the scope a factor in your case too or can you reach the knob good?
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I just mounted a scope, and it's not too bad to cock at all.... actually much easier than a round knob.... You can sneak your index and middle fingers in flat under the scope, there is lots of room to hook them on the handle securely and pull straight back.... You may have to lift your cheek off the stock a bit depending on if you're a stock crawler.... I think it's far superior to a round knob, I've had those slip from my fingers and fire while cocking.... not the nicest of feelings....
Bob
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As would I for the same reason plus it must be much more comfortable as well where I could see getting knob rash from a round knob if using a thick spring at max adjusted power. I used to get bolt rash on my index finger when using the .047" spring with the bnm knob since it was so thin. I personally think yours just looks better than a round knob as well.
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In case anybody is interested.... I used a 3/4" mill and the notches are 1" apart C-T-C.... Total width is 1.6", depth is 0.4", material is 3/8" thick 6061-T6.... Everything else pretty much falls into place.... The cocking rod / spring guide is a piece of 7/32" drill rod (works perfectly with the QB spring) and it's turned down to 3/16" and threaded 10-32 on both ends.... with the hammer (and handle) drilled and tapped to match.... after installing the guide in the hammer (tight, with blue loctite), chuck it up in the lathe and make sure the rod runs true (turning it by hand).... If it doesn't, bump it with the crossfeed on the high point until it starts to bend.... Check it again, and repeat, turning the crossfeed in 0.010" further each time until it runs true.... The RVA screw (3/8-24 NF) is drilled 15/64" from the back end for most of it's length, with the inner 1/8" drilled with a #2 drill (0.221").... If that's too snug, use a #1 (0.228").... The guide must slide easliy through the RVA screw no matter what the orientation or stroke position.... If you're using this on a Disco spring, use 3/16" drill rod and a smaller hole in the RVA adjuster....
Bob
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Bob,
Coming along nicelt. you are doing so amazing work. I bet is a very loud gun. Are you going to but a shroud on it once your barrel comes in?
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This is a very interesting Project! I bet it turns out awesome! Heck everything you do turns out amazing!
Thanks so much for all the info you post! I enjoy reading it so much!
Bruce
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This gun will have a shroud, but not one that will affect the noise level of the gun, they are prohibited in Canada, unfortunately.... I will be using a 7/8" OD x 3/4" ID Carbon Fibre tube located on two 3/4" bosses, one on the front of the breech, and the other on the back of this modified Hatsan air stripper.... These strippers are available in .177, .22 and .25 cal (shown), having different inserts for the different bores.... The brass insert is adjustable fore-and-aft to adjust the air gap between it and the muzzle, which can have a dramatic effect on accuracy.... I will be making a .30 cal insert for the stripper on this gun....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3441_zps06fd2123.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3441_zps06fd2123.jpg.html)
The rear portion of the stripper was tapered, but I turned a parallel section with a 3/4" diameter up to where the stripper was 7/8" OD (where the shoulder is).... It will thread onto the end of the barrel on standard 1/2"-20 NF threads.... The shroud will mount between the bosses on the breech and stripper, and when the stripper is tightened up, the shouders will put the shroud in compression and the barrel under tension.... which should stiffen the barrel and raise it's resonant frequency.... In theory, this should reduce or eliminate the effect of barrel harmonics.... which can be quite a problem on long, thin barrels.... In addition, the woven finish of the CF tube should look pretty KEWL.... Once in place, all three tubes will be the same diameter, and also the same width as the breech....
Bob
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HI Lloyd, thanks for chiming in.... much appreciated.... I used 1010 mild steel with a 44K yield in my calculations, and with three screws all taking equal load, I get a 0.150" contact width per screw required at yield at 3000 psi.... in other words, if the yield strength is 44K, with 3 screws, they in theory should "settle in" and stop moving after that.... Using a 0.312" hole and a 0.270" head, that means the screw has to move 0.004" aft.... for a total of 0.025".... This is assuming, of course, that all the holes in the valve and the tube are drilled in EXACTLY the same plane, which is VERY unlikely.... I didn't duplicate the calculations using 70K for the compressive strength of the tube because I don't know what material it is.... but CrMoly is only 63K yield IIRC?....
Anyway, I overestimated how far the valve is likely to move back, but since I've seen a fractional settling in even with a 5/16" head size on the 10-32 screws at 3000 psi (I thought you had as well?).... I think we can assume that the valve might, on average, end up about 0.025" further back than it should.... but we can also assume that once it has settled into it's new position it should be perfectly safe.... wouldn't you agree?.... Sorry if I first erred on the side of caution....
Bob
Bob,
Sounds like we are pretty much in agreement on this, and I agree that the full dia 5/16" heads are by far the best choice. The 72ksi compressive yield figure for the tube that I used is for A513 Ty 5 DOM steel tube which is basically strain hardened 1020. I could be wrong, but that is a good guess for many air tubes (A513 Ty 5 DOM 72ksi Y, 87ksi UT; 4130 Normalized tube 63ksi Y, 97ksi UT) . Plus it is much cheaper and threads more nicely IMO.
Lloyd
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Sean and I discussed what direction we wanted to go with this project, and decided that we may as well max out the performance and then he will supply a smaller transfer port with the kit so that people can detune the gun easily for more shots.... We also decided to set the gun up for a 3000 psi fill by using 10-32 screws to mount the valve.... With that in mind, I pulled the valve, installed the larger screws, drilled the throat out to 1/4", and enlarged the exhaust port to 7/32", the same size as the transfer and barrel ports.... Here are the results, still using the 21" PB barrel and the .308" upsized pellets.... We expect a bit more with the 25" barrel....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DDoubleShortBarLargePorts_zps2f9168c5.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DDoubleShortBarLargePorts_zps2f9168c5.jpg.html)
The power at 3000 psi with the preload at coil bind is now 105.7 FPE.... At 2 turns out, the first 3 shots are nearly constant velocity at 101 FPE, and at 4 turns out there is a very good 8 shot string averaging 949 fps (92 FPE) starting from 3000 psi and dropping to 2100, with an efficiency of 0.78 FPE/CI.... Since the magazine will hold 7 shots, this tune will give a full clip at maximum power, a good choice for hunting.... At 6 turns out, the gun is the most efficient, delivering 10 shots averaging 915 fps (86 FPE) at 1.05 FPE/CI, from a 2700 psi fill and refilling at 1900 psi.... At 8 turns out, the power is down to 78 FPE, still at 10 shots, with a pressure range from 2400 down to 1600 psi.... I particularly liked the way the gun shot at 5 turns out (the black line) where it gave 9 shots averaging 937 fpe (90 FPE) from 2800 psi down to 2000 with an efficiency just under 1.0 FPE/CI....
The barrels are now here, and Sean will be chambering my barrels and I hope to have them within a couple of weeks.... Then I just have to find enough time during our coming busy Tourist Season to do the necessary work to install and test them.... I have two .30 cal barrels coming, one of which Sean will be choking, plus a .25 cal for testing the gun with 53 gr. cast bullets, and the 47 gr. hollowpoint version as well.... I'm really looking forward to seeing the results....
Bob
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Awesome progress and great numbers!!!!!!! the longer barrel should up the numbers even more if you want!
Congratulations!
Bruce
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I couldn't do any more testing until I get the new barrels.... so I decided to see how this barrel would shoot with cast bullets.... I pulled the barrel off and increased the chamber length with the reamer I made so that it would chamber a 118 gr. Lee FN, cranked the RVA to maximum preload, and fired a string across the Chrony.... It was one of those rare times when having the gun maxed out was the perfect solution, I was rewarded with a beautiful 7 shot string with a 4% ES....
667
680
687
693
687
684
670
The peak energy was 126 FPE, the average was 122 FPE, and the efficiency was 0.80 FPE/CI.... which is not bad considering the power level.... This is almost as much power than I got with my 9mm Disco Double, and more than I got with the .308 version, both of which were 24" barrels.... so I was very pleased with the results.... This really has nothing to do with this project, it was just a matter of satisfying my curiousity....
Bob
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Thanks for publishing the fine work Bob. I am getting a serious case of the shakes over making the next set of Marauder valve mods; bigger holes are definately called for...:) and what you have gotten leaves me confident in its ability to deliver near 100 FPE energy with 50-53 gr castings. getting peller-cheap boolits is quite another story...LOL and an order for my Very First Mold should be completed today.
cheers,
Douglas
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ooops...gonna have to delete this one
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It will be tougher to get 100 FPE with 50-53 gr. in .25 cal than in .30 cal of course.... Not impossible, but the larger area gives more force for acceleration in the bigger bore.... Having said that, the much higher SD of the cast bullet in .25 cal will allow you to keep the valve open longer without loosing too much efficiency.... or so goes the theory.... I'll be doing the same thing, once the new .30 cal barrel is installed and tested I will be putting a .25 Auto liner on the gun and seeing what I can get with cast 47 gr. HP and 53 gr. Solid .25 ACP bullets from an RCBS mold.... I'm thinking I may even try a .357 liner chambered for the new 78 gr. JSB pellets after that....
Bob
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It will be tougher to get 100 FPE with 50-53 gr. in .25 cal than in .30 cal of course.... Not impossible, but the larger area gives more force for acceleration in the bigger bore.... Having said that, the much higher SD of the cast bullet in .25 cal will allow you to keep the valve open longer without loosing too much efficiency.... or so goes the theory.... I'll be doing the same thing, once the new .30 cal barrel is installed and tested I will be putting a .25 Auto liner on the gun and seeing what I can get with cast 47 gr. HP and 53 gr. Solid .25 ACP bullets from an RCBS mold.... I'm thinking I may even try a .357 liner chambered for the new 78 gr. JSB pellets after that....
Bob
I got one from Veral, and found a 252435 on the auction site. You have any idea what the marking FW after the model number means? The 100 FPE is jus' a number...I don't think I will be able to live with its efficiency at that power level. Upper 800's will be fine...:)
cheers,
Douglas
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Don't know what the "FW" means....
Bob
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Bob
I really like that #3 and #4 string. I'd like them even more if they were shifted up about 5%.
And I think its possible with a really good barrel. With that in mind I think a full length taper lap with ultra smooth finish is a must on the barrel that's getting the choke. It only seems fair to see just how much of a powerhouse you've got there.
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Just took an hour and read all six pages, all I can say is WOW.....
Can't wait to see the finished project....
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HEY Sean.... Welcome back to the land of the living.... *grin*.... If you want to do that fancy lap job, be my guest.... *LOL*....
I can't wait to see the new barrels.... We'll lose a bit of efficiency with the 0.008" smaller bore, but should gain way more with the 4" increase in barrel length.... It was nice to hear that the pellet fit in the new barrel was spot on.... full rifling engagement on the head without shaving it from the groove diameter.... It was also good news that the first order is nearly sold out and you will have to get some more already.... (gentle nudge for anyone still interested to send a PM to SeanMP to get in on the second order)....
Bob
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I need to get off my butt and put that 29" barrel to use..
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I need to get off my butt and put that 29" barrel to use..
Hey, I'm gonna take a wild guess and say you got it okay then?
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Okay Bob here is the finished chambering ream
The leade is subtle at 1.1* This is what the angle worked out to that will hold the head and the skirt equally.
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I did and thank you. Just curious how the unchocked barrel will do with the 50 gr pellets.
I need to get off my butt and put that 29" barrel to use..
Hey, I'm gonna take a wild guess and say you got it okay then?
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All the blanks are unchoked.... I'm having Sean roll a choke into one of the two I'm getting so that hopefully I can answer that question....
Yeah, that's a shallow leade, Sean.... I'm trying to figure out your reamer, is the portion between the front of the pilot and the smallest part of the leade undercut so that it doesn't touch the rifling?....
Bob
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Ya that's it exactly Bob. It gives a bit of distance between the pilot which has minimal clearance and the business part where the swarf is.
You can see the same idea going on here in the cartridge reamer pic
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Okay Bob your barrels are ready to go
First they were dialed true to the axis. Concentric and axial to 0.0001"
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Then the chamber was cut
Then the barrel was flipped and the choke rolled in
(http://)
After that the lead lap was cast at the muzzle
And after a thousand strokes we have a tubular mirror with a slight taper
(http://)
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Very cool, Sean.... looking forward to getting them.... 1000 strokes?.... WOW !!!
Bob
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I'm just catching up on the progress here, and am finding it fascinating.
Sean, that is one of the barrels from Mike Sayers, correct? And you are doing a choke plus a taper lap, correct?
Do you have a mechanical set-up to do the lapping, with an ever increasing stroke length or something of the sort? I really like the taper reamer you made for the breech.
Just so that I fully understand, the main reason for all the attention to detail on the barrel is for accuracy, correct? But you also mentioned the possibility of increased fps?
Thanks for any additional insight you might have to offer,
Lloyd-ss
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Sean
did you make this reamer ?
Okay Bob here is the finished chambering ream
The leade is subtle at 1.1* This is what the angle worked out to that will hold the head and the skirt equally.
(http://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=46367.0;attach=62444;image)
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Yes, he did.... He makes custom reamers to do all his airgun chambering jobs....
Bob
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I got my new barrels today from Sean, and all I can say is WOW !!!
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3522_zps07bcc674.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3522_zps07bcc674.jpg.html)
He machined the chambers, crowned and choked one of them and taper lapped the bore (1000 strokes), and then even polished the outside.... It looks like Chrome inside and out, I can't wait to see how it shoots.... The JSB .30 cal pellets are a PERFECT fit in the chamber and engage the leade beautifully, leaving good rifling marks on the head, but without smearing the area between....
In addition, he shipped me some of the CF Shrouds, and even cut them to length.... I had previously machined a Hatsan air stripper to fit inside the end of the shroud and made a .30 cal insert for it.... and it slid inside perfectly.... The shroud is 7/8" OD, to match the Disco and Disco Double tubes.... It will end up in compression, with the barrel in tension, when the stripper is snugged into place on the threaded muzzle....
Now to find some time to machine in the O-ring groove in the breech and the barrel port and thread the muzzle for the stripper....
Bob
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I'm just catching up on the progress here, and am finding it fascinating.
Sean, that is one of the barrels from Mike Sayers, correct? And you are doing a choke plus a taper lap, correct?
Do you have a mechanical set-up to do the lapping, with an ever increasing stroke length or something of the sort? I really like the taper reamer you made for the breech.
Just so that I fully understand, the main reason for all the attention to detail on the barrel is for accuracy, correct? But you also mentioned the possibility of increased fps?
Thanks for any additional insight you might have to offer,
Lloyd-ss
Lloyd sorry for the delayed response...I have also had my nose on the grindstone for the past month trying to catch up after being away for 11 weeks.
Yes that is one of Mike's barrels. And yes I'm putting a choke in and lapping them. Bearing in mind that the taper is minuscule. It only ensures that the projectile is tight to walls all the way up the bore.
Yes this is done primarily for accuracy but I have found in every case that there is an increase in fps after the bore is properly lapped and polished. Bob has found the same as well. I think the main reason for this is because the pellet is maintaining a seal on a very smooth surface.
I do my lapping by hand. And personally I think that is a job that only be done manually because it is very much a "feel" process. First your feeling for slight drag and release to tell you that there are tight/loose areas or chatter that indicates machining marks and then feeling the equal drag that tells you the bore is parallel. Then your feeling for an increase or decrease in drag to indicate your taper. All the while feeling for when to tighten the lapped based on drag.
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Bob....All I can say is WOW!
The shroud and the stripper are going to look amazingly bad.
Sweeeeet!
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Sean,
Thanks for the additional info on the barrel processing. I understand what you mean about lapping the barrel. The "golden arm" technique with lots of patience where it is more art than science. The increase in fps is good information.
Bob,
Putting the barrel in tension adds another variable to the accuracy tuning process, LOL. Tensioning for a specific pellet and velocity, and my guess is that it just might be tuneable that way. Maybe?
Lloyd
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I agree, it may very well be possible to tune for a specific pellet and velocity with the barrel tension.... I haven't played with that before, so another variable, which can be good or bad.... The adjustable gap on the air stripper is yet another tuning point, and one I have heard can make quite a difference....
Bob
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We had a slow week at the Motel, so I got a chance to get into the shop and machine the O-ring groove and port into the new barrel today.... I shortened the shroud so that when the air stripper is tightened the muzzle is just clear of the front of the threaded section of the stripper and got to take a look at the new gun assembled for the first time.... It still needs some parts blued, but here is the first photo with the new barrel, shroud and stripper in place.... The gun weighs exactly 8 lbs. and I'm extremely pleased with the appearance.....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3527_zpsc4058736.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3527_zpsc4058736.jpg.html)
The first shot over the Chrony was 1045 fps, but my tank need topping up, so after 3 hours on the ShoeBox, after dinner I got to shoot a set of strings.... I filled to 3000 psi and shot until the velocity dropped 4% below the peak in each case.... The last 4 strings required less than a 3000 psi fill, as I was reducing the hammer spring preload for each subsequent string.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleShotStrings_zpsb4420d11.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleShotStrings_zpsb4420d11.jpg.html)
Maxed out, the first shot was the fastest at 1049 fps (112 FPE).... At 4 turns out, I got 10 shots that were within 4% ES, and they averaged 975 fps (97 FPE), peaking at just over 100 FPE.... The efficiency was 0.91 FPE/CI, filling to 2900 and refilling at 1880.... At 7 turns out, I got 12 shots averaging 912 fps (85 FPE), with an efficiency of 1.11 FPE/CI.... The fill pressure was 2400, refilling at 1520.... I think if I installed a slightly smaller transfer port I could stretch the string to 14 shots (2 clips)....
I'm very pleased with these initial results.... With the first serious testing of the new barrels producing MOA acccuracy out to 100 yards, this should be a serious hunter.... I'm looking forward to getting the new 7 shot magazines from Lloyd at AirGunLab.... He has converted .25 cal MRod magazine to .30 cal, and they look gorgeous.... My breech was made to fit them....
Bob
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Since this gun is going to have a 7 shot magazine, I was curious what I could get for 7 shots starting at 3000 psi.... Here is the string....
984
1000
1007
1003
997
993
981
Average fps = 995
Average FPE = 101.1
Total FPE = 708
Press. Used = 750
psi / shot = 107
Total CI Used = 786
FPE/CI = 0.90
% ES = 2.6%
I'm thinking this is a heck of a Coyote gun....
Bob
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Most impressive !!!
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Bob, that is a heck of a gun period. If you must put an application to it, I think it would be best stated as a,"anything under 80lbs gun". ;D have you looked at what the retained fpe is at 100yrds yet? I don't bet, but if I did, I'd bet that your bullet has more fpe than a .22LR does at 100 yrds. I missed what the .30 jsb weight is but if it is greater than 40gr, There is a good chance I'm right.
yes, MOST impressive.
Bill
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The BC of the new 46 gr. JSB pellets (they also make a 50 gr. I haven't received yet) is unknown at this time, but I'm guessing it's quite a bit less than a 40 gr. bullet from a .22LR.... Starting subsonic will help, of course, but I don't think it will quite have the FPE of a .22 LR at 100 yards.... Momentum is another thing, they may be close....
Bob
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Bob, that is a heck of a gun period. If you must put an application to it, I think it would be best stated as a,"anything under 80lbs gun". ;D have you looked at what the retained fpe is at 100yrds yet? I don't bet, but if I did, I'd bet that your bullet has more fpe than a .22LR does at 100 yrds. I missed what the .30 jsb weight is but if it is greater than 40gr, There is a good chance I'm right.
yes, MOST impressive.
Bill
I guessed on the BC of 0.05, everything else is straight from his data....
Your Input Variables
Ballistic Coefficient 0.05
Velocity (ft/s) 995
Weight (grains) 46
Maximum Range (yds) 100
Ballistics Results Range (yards) Velocity (fps) Energy (ft.-lb.) Trajectory (in) Come UP in MOA Come UP in Mils
Muzzle 995 101 -1.5 0 0
25 909 84 3.3 -12.5 -3.6
50 843 73 5.4 -10.3 -3
75 787 63 4.5 -5.7 -1.7
100 738 56 0 0 0
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56 fpe at 100yrds. 55% retained energy? That is impressive. It is getting to the point with airguns, that the only reason for a powder burner is for ranges that exceed 100yrds and a need for supersonic bullet delivery. It is awfully hard to beat supersonic bullet delivery in regard to effect on target.
Absolutely B--A-- gun
Bill
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I shot my .30 build over a chrony at two different distances to calculate BC for the 44gr JSB pellets and came up with @ .042 for the BC. I've not done the 50gr pellets yet.
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That's a good looking powerhouse of a gun Bob. Great work and thanks for bringing us along on the journey. Now for a post in the Hunting Gate!
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I shot my .30 build over a chrony at two different distances to calculate BC for the 44gr JSB pellets and came up with @ .042 for the BC
At what velocity (and distances).... that will affect the results.... Seems like a reasonable value, though....
Bob
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starting about 10 feet from the muzzle for the near, and right at a measured 50 yards for the far. Velocity was kept in the 880's with the average being 887fps.
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looking awesome!
Bob, are you having issues getting the 50.15 JSB? If you need a few for testing I could send you a few. I only have 2 tins of JSB 50.15 and 1 tin of Daystate Emperor so I can't spare a full tin. I expect will be shooting cast more than pellets in our barrel but only time will tell.
Bruce
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DG.... In that velocity range, over most of the distance, and from my experience with smaller calibers of JSB Exacts, you should be in the "sweet spot" for the BC.... If you push them faster I would expect the BC to drop....
Bruce.... no joy on the 50 gr. but I think I have a source lined up for a sleeve of 5 tins, thanks.... *fingers crossed, waiting for a PM*....
Bob
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thanks for the confirmation, Bob... But, I have to tell you a have a wee bit of experience with cobbling something together. It wasn't really an accident that I set up to figure the BC of the .30 pellets the way that I did.
(http://davegcustomstocks.com/trident_ba_crusader_1raw.jpg)
I just finished the last pieces for this one yesterday late afternoon. I will be working on getting it completely finished over the next couple of days once I am happy with the target results.
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Thing of beauty.... Your work looks familiar, but the moniker threw me.... What barrel are you using?....
Bob
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Dave
i have to agree with Bob
that is a thing of beauty :P
worth drooling over ;D
thanks for the confirmation, Bob... But, I have to tell you a have a wee bit of experience with cobbling something together. It wasn't really an accident that I set up to figure the BC of the .30 pellets the way that I did.
(http://davegcustomstocks.com/trident_ba_crusader_1raw.jpg)
I just finished the last pieces for this one yesterday late afternoon. I will be working on getting it completely finished over the next couple of days once I am happy with the target results.
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don't want to hijack Bob's thread. Worthy build he is working on, and I don't want this to become a distraction from the original content of the thread...
Bob, I work largely with Smooth Twist barrels, but not exclusively. My .30 builds thus far have all been ST's, which I feel work brilliantly with the JSB pellets. For heavier ammo in the same caliber, I am looking to follow the results you guys are getting with the TJ's.
I generally don't produce an action to work with pellets or cast ammo, but rather purpose build for the intended ammo...
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I agree.... For cast bulets, I would stick with the standard 0.308" bore size.... there is a much larger choice of molds / bullets available.... Much like in .25 cal, for pellets stick with 0.250", for bullets, go to 0.257" with a faster twist.... although you can use the 50 gr. .25 ACP bullets in an airgun barrel.... I have a .25 Auto liner from TJ's that I will be putting on this gun and setting it up to shoot up to 53 gr. casts that will fit in an MRod magazine....
Bob
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I finally got back to this project today.... I received some of the converted Marauder magazines from Lloyd at AirGunLab and had a chance to finish them up.... If you are interested in these .30 cal magazines, I suggest you contact Lloyd to enquire about them.... http://www.airgunlab.com/ (http://www.airgunlab.com/) .... As yet, they are not on the website.... Here is how they look, along with a .25 cal single shot tray I modified by increasing the diameter of the channel to fit the .30 cal pellets....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3612_zps775d1ac5.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3612_zps775d1ac5.jpg.html)
Lloyd starts with a .25 cal MRod magazine and has a new 7-shot star wheel made by CNC for the larger pellets.... It is engraved with the shot numbers, which I filled in with white paint to make them more visible.... In addition, the clear plastic cover is changed to read .30 cal, and the kidney bean shaped hole is enlarged as well.... On the magazines I received I still had to drill out the hole in the back to feed the larger pellets.... I centered off the original hole, and used a 5/16" end mill for that.... When I reassembled the magazines I added 1/3 turn of tension to the spring to compensate for the larger pellets.... It may have not been necessary for feeding, but they certainly do advance with authourity, and the skirts are so thick on the .30 cal JSBs I can't imagine the slight increase in spring tension causing any damage....
I'm in the process of mounting a scope and hope to do some testing soon....
Bob
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After three months of waiting for Airguns of Arizona to come through with my pellets I cancelled the order and got them from Specialty Shooting Sports.... I originally ordered the 50 gr. JSBs from AoA and they (knowing they were incorrect) shipped the 45 gr.... I told them I'd keep those and to ship the 50 gr. when they came in (in a month), and after 2 months I contacted them and they told me JSB didn't ship them.... After chewing them out (again) for not letting me know, they agreed to substitute the Daystate 50 gr. (same pellet but more expensive) when they arrived in 2 weeks.... A month later I called them yet again and found the Daystates hadn't arrived either (and once again they didn't let me know), so I cancelled the order and got them in 3 days from SSS.... Anyway, that is the reason for the lengthy delay in getting back to this project....
I now have the 7-shot converted mags from Lloyd at AirGunLab, and after a bit of tuning to function with my flat faced bolt, they function flawlessly.... I had four pellets to test now, some #1 Buck from Ballistics Products, 44.8 gr. JSBs, 46.4 gr. FX, and 50.2 gr. Daystates.... I weighed 10 of each and they came out at follows:
#1 Buckshot - 39.6 gr.
JSB - 45.2 gr.
FX - 44.8 gr.
Daystate - 49.4 gr.
The #1 Buck were rather inconsistent in diameter, running from 0.294" - 0.302", with most between 0.296"-0.300".... While they were too loose in a 0.308" PB barrel, or the one on my DAQ, they worked perfectly in our new 0.300" barrel, and chambered easily (without the small ones rolling out the muzzle like they did on my DAQ).... The JSB and FX pellets are from all measurements exactly the same.... The previous tins of FX pellets I had weighed 45.3 gr, so it would appear that 44.8 to 45.3 is normal for both brands.... The Daystate pellets are exactly the same length as the FX, and they are availlable under the JSB label as well, I just haven't been able to get any.... The extra weight comes from a thicker waist, they measure 0.257" instead of 0.214".... All the pellets shot into one (large) ragged hole during my indoor Chrony session, although the roundball group was nearly 1/2" OD whereas the others were more like 3/8".... It's very satisfying to see a big hole appear in the paper and then see the rest of the shots go through it, barely enlarging it, even when shooting at only 20'....
I started out with the hammer spring preload set just shy of coil bind, and tested all four pellets at that setting.... The roundball screamed through the Chrony at 1079 fps and 102 FPE, the JSB & FX 45 gr. weren't far behind at 1050 (110 FPE), and the Daystate 50 gr. hit 1015 fps (113 FPE).... The roundball were really just a curiousity, and I had already extensively tested the 45 gr. FX pellets, so I used the Daystate 50 gr. for the rest of the tests.... I reduced the preload a turn at a time, recording all shots within 4% of the peak velocity in each string, as follows:
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleVelocity_zpsb7743b59.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleVelocity_zpsb7743b59.jpg.html)
At 1 turn out on the preload, I got a 7 shot string (1 full clip) averaging 988 fps (107 FPE) with all shots within a 2.8% ES, and the first 6 shots within 1.8%, with an efficiency of 0.92 FPE/CI, pretty decent for over 100 FPE.... At 2 turns out, the shot count with a 4% ES jumped to 10 at 102 FPE, still starting with a 3000 psi fill (ending at 2200) with an efficiency of 0.99 FPE/CI.... At 3 turns out, the fill pressure was 2800 psi, and I got 11 shots at 97 FPE at 1.05 FPE/CI and at 4 turns out, using a 2700 psi fill, I got 11 shots averaging 94 FPE at 1.09 FPE/CI.... Any of these tunes would be very usuable, and selecting the 7-shot sweet spot at the top of the curve would give minimal POI change, even out to 100 yards.... at peak velocities of 940, 960, 980, or 1000 fps (with the 50 gr. Daystates) depending on choice of preload and hence fill pressure....
Testing at longer ranges is problematic at the moment as pressing family matters and travel is going to detract from my target time.... However, with two weights of pellet to choose from, and the ability to fine tune the velocity, I would expect to find at least one combination that proves stellar....
Bob
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Bob, my good man, you have done it again! Your attention to detail always makes the big difference, IMHO. Even though you haven't thoroughly tested it at long range, I am sure that with Sean's barrel, the end result will be striking. An honest long range hunting gun.
You mentioned the 7 shot 30 cal mags that I made for this project. Even though I do not yet have them on the AirgunLab website, I will certainly make them available to anyone using one of Sean's barrels. Other responsibilities continue to keep my airgun time at a painfully low level, but there is an end in sight where I will be able to ramp the airgun effort back up. It is still a few months away, but I'll be back.
Lloyd
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I finally had a chance to get the gun out for some long range shooting today.... It is tuned for one 7-shot clip at 107 FPE with the 50 gr. Daystates (988 fps) or 105 FPE with the 46 gr. FX/JSB pellets (1012 fps).... I first shot a 3-shot group with each pellet at 50 yards, and they were all under a quarter, with this being the best....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30Disco50yd_zpsc0149a73.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30Disco50yd_zpsc0149a73.jpg.html)
That measures 1/2" C-T-C.... I then shot a 5-shot group with each pellet at 100 yards.... Here are the targets....
Daystate 50 gr.
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30Disco100ydDaystate_zpsa05a2238.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30Disco100ydDaystate_zpsa05a2238.jpg.html)
JSB 45 gr. (higher aim point)
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30Disco100ydJSB_zps5328e419.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30Disco100ydJSB_zps5328e419.jpg.html)
FX 46 gr.
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30Disco100ydFX_zps5f3cf2c5.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30Disco100ydFX_zps5f3cf2c5.jpg.html)
There was a slight wind swirling around though the trees.... Four of the five shots in each group are within 1.0" - 1.2", and the average group size was under 2" except for the 1 shot I pulled.... I didn't do any tuning of the air stripper, nor did I check to see if the accuracy is any better at a slightly lower velocity.... To be frank, I wasn't shooting at my best in the cold weather, it was just above freezing today, and I know for a fact I pulled the one FX pellet up and to the left.... Overall, I'm very pleased with the groups for a first time out.... I stapled a pellet tin (2.5" D) to the 100 yards support and nailed it first shot.... All three pellets print at very nearly the same POI at 100 yards....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3767_zpsd746caac.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3767_zpsd746caac.jpg.html)
The development work on the .30 cal version is now complete, and it's time to start work on the .25 cal barrel.... This testing certainly proved that the .30 cal barrel Sean and I designed for the .300" head size JSB pellets does the job....
Bob
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Hmmm....Awesome!
Excluding the called flier that FX group is actually sub MOA. Excellent!
I think it would be safe to assume that with tuning this would improve.
Thats quite an achievement. Sub MOA with an air rifle shooting pellets is remarkable....something high end bolt actions only achieve after some tweeking.
nothing like setting the bar up a notch ;D
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Before leaving the .30 cal, I had one more thing I wanted to try.... The bolt on this gun is probeless, you push it forward to seat the pellet, turn the handle down, and then retract it clear of the barrel port.... It occurred to me that if I had an adjustable stop in the "J" slot I could set how far back the bolt retracts, and hence use the nose of the bolt to restrict the barrel port.... Here is a photo of it installed in the breech....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3800_zps811e14d1.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3800_zps811e14d1.jpg.html)
I drilled a 3/32" hole in line with the "J" slot from the back of the breech, then drilled in and tapped the back of it for a 1/2" long 6-32 SHCS.... The screw pushes on a 0.8" long brass pin for the bolt stop, which can be adjusted from fully open to stopping the bolt with the nose virtually at the front of the barrel port.... The screw might have a tendency to back out, so I drilled up from the bottom of the breech, near the back, and installed a 1/4" long piece of 0.095" weedeater line pressed against the adjusting screw by a 6-32 setscrew to provide a "brake" by adding friction so it won't self-adjust.... Everything worked great, so I proceeded to testing it....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleAdjuster_zpsbeceb819.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleAdjuster_zpsbeceb819.jpg.html)
I ran the adjuster in all the way, filled the gun to 3000 psi, and fired two shots.... turned the screw out a turn and fired two more, and repeated until the stop pin was flush with the end of the shot and therefore having no effect.... The purple stepped line on the graph above shows the results.... 310 fps, 550 fps, 740 fps, 870 fps, 950 fps, 980 fps, and just over 1000 fps.... There was no change in velocity for the last turn, it was the same completely clear of the "J" slot or 1 turn (0.032") in.... I turned the screw in 2 turns from maximum and backed off the hammer spring preload a turn (the measurements on the graph, eg. 0.337", are the preload, which moves 0.042" per turn) and shot a string.... My goal was two 7-shot magazines (ie 14 shots) at the highest possible FPE level within a 4% ES.... I played around with a few settings, and three of the 14 shot combinations are on the graph above.... It took the adjuster screw turned in 2.5 to 3.0 turns to get my 14 shot strings, and I ended up with the following:
86.6 FPE average at 1.08 FPE/CI
84.0 FPE average at 1.14 FPE/CI
82.7 FPE average at 1.18 FPE/CI
With the gun set for a single 7 shot string (1 magazine) at maximum FPE, it shoots 101.2 FPE at 0.90 FPE/CI with all the shots within 17 fps (1.7% ES).... All these strings are with the JSB 45.2 gr. pellets, the FPE levels are slightly higher with the 49.4 gr. Daystate pellets, averaging 107 FPE over 7 shots.... I have no doubt that by turning the velocity adjuster in more I could achieve more shots at less power, but two full magazines at 83-87 FPE is a good compromise.... I'm very pleased with the way the .30 cal version of this gun turned out.... When time permits, I will be getting on with fitting a .25 cal barrel to see what can be achieved when set up as a quarterbore....
Bob
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Is the end of the probe flat? If it is, what do you think would happen if the business end of the probe was scalloped out a bit for air flow purposes or does the o-ring position allow for this? Regards, Tom
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I drilled a 3/32" hole in line with the "J" slot from the back of the breech, then drilled in and tapped the back of it for a 1/2" long 6-32 SHCS.... The screw pushes on a 0.8" long brass pin for the bolt stop, which can be adjusted from fully open to stopping the bolt with the nose virtually at the front of the barrel port....
While reading this, I found myself involuntarily yelling "YEEEEEESSSSSSSSSSSSSSSSSSS!!" (My wife thought I'd won the lottery, or something else equally pleasing. She was not happy when I responded to her query with, "Bob made the best stupid-simple power-adjuster, ever!")
Sometimes the simple things are best.
I honestly cannot wait to get a breech like this. I don't even have a PCP--I don't care if it's for my espresso machine. I just like things that do their job well, with a minimum of fuss. I like it Aristotelian, yo.
You just made my weekend.
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You can incorporate this into a Marauder pretty easily. I am having the pull-back/probeless done for my .224 Marauder. Looking at the spare 2563 breech, there is plenty of meat available to run the adjustable stop into. I don't see a marauder in your sig tho...????
cheers,
Douglas
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I don't see a marauder in your sig tho...????
Nope...
I don't even have a PCP--I don't care if it's for my espresso machine. I just like things that do their job well, with a minimum of fuss. I like it Aristotelian, yo.
I just think this is so awesome, I want it to hang on my wall: "This is an example of something that is simple and effective."
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The end of the bolt is flat (there is no probe), scroll back through the thread for details.... It has to be flat to load the pellet squarely in the bore as it pushes on the outside of the skirt.... In "full power" operation it retracts completely, flush with the back of the barrel port.... and presents NO obstruction to the airflow.... One other advantage is that it will load bullets and pellets to the same place in the bore, just the other side of the barrel port.... All the adjuster does is limit how far it can retract....
Bob
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Just meant like this, though not quite as deep. Regards, Tom http://imageshack.com/scaled/large/802/tt8j.jpg (http://imageshack.com/scaled/large/802/tt8j.jpg)
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Broken Link....
Bob
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I just tried it by clicking and copy-pasting in address bar, worked both times. Regards, Tom
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Tom
it doesn't work for the rest of us
gives this error message
Unable to read source image dimensions
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Try this one http://imageshack.com/scaled/large/849/fcr0.jpg (http://imageshack.com/scaled/large/849/fcr0.jpg) , I'm so embarrassed, I had deleted all the pics in imageshack, I must have been getting it from browser cashe. Regards, Tom
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I got a chance to machine the .25 cal barrel and install it yesterday.... I reamed the chamber with a reamer I made myself (thanks Sean for the guidance).... I cut the chamber in the TJ's .25 ACP liner (14" twist) to fit both pellets and bullets, and it should handle anything that will fit in an MRod magazine.... I then machined the O-ring groove and barrel port, using an oblong port measuring 3/16" x 1/4" which has the same area as the 7/32" transfer port I used for the .30 cal version.... I removed the .30 cal barrel, installed the new .25 cal in the breech and started testing....
I cranked the RVA to just shy of coil bind, left the screw that adjusts the bolt in the wide open position, filled the gun to 3000 psi and tried a few shots with different pellets / bullets to find out the maximum the gun could deliver, with the following results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleMaximums_zps1f2a2692.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleMaximums_zps1f2a2692.jpg.html)
Just as the .30 cal exceeded my expectations, so did the .25 cal.... The maximum power is down about 16 FPE compared to shooting simlilar weight pellets in the .30 cal version, as could be expected.... I then proceeded to shoot some strings, and I found out that with the 52.7 gr. RN bullets I have to run the RVA nearly at coil bind (in fact just 1/2 turn out) to get the best string with a 3000 psi fill at maximum power.... Here are the results of testing with those bullets.... The bullets were unsized, and I think the variations in diameter as cast are causing the shot to shot variations in the strings....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleRNBullets_zps9ab30781.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleRNBullets_zps9ab30781.jpg.html)
When I turned in the velocity adjusting screw (which causes the nose of the bolt to partially block the barrel port) I found that I had to back the RVA out 1 turn to get the best strings.... Here is a summary of the averages for each string shown on the graph....
Maximum: 894 fps (93.5 FPE) for 9 shots at 0.80 FPE/CI
3 turns in: 856 fps (85.8 FPE) for 12 shots at 1.02 FPE/CI
4 turns in: 827 fps (80.1 FPE) for 15 shots at 1.04 FPE/CI
5 turns in: 779 fps (71.1 FPE) for 17 shots at 1.07 FPE/CI
6 turns in: 712 fps (59.3 FPE) for 21 shots at 1.15 FPE/CI
I didn't test the gun with the velocity adjuster in 7 turns.... It wouldn't have been in the 300 fps range like it was with the .30 cal because the oblong barrel port would not have been as completely blocked by the nose of the bolt, and I didn't care about velocities below 700 fps anyway.... In the next post I'll tell you what happened when I switched to the JSB Kings....
Bob
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Tom, I thought understood what you meant, but I wanted to see the photo to make sure.... I don't see how that could work in my application.... You would have to load the pellet whatever length the "streamlined" portion was ahead of the barrel port in order for the full diameter portion to obscure the port.... That extra wasted volume behind the pellet would surely take away from any theoretical advantage to turning the flow smoothly around the corner.... Your setup I'm sure works great when positioned as you would at full power and with a non-retracting bolt.... but with a bolt where you seat the pellet and then retract it to the firing position, you would be loading the pellet further forward than necessary or desireable.... unless I'm missing something?....
Bob
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Awesome 25 results Bob!
You're right where I'm at with the Double Tube - I'm getting 10 full power shots and consuming 70 psi per shot.
I'm really eager to see how your TJ barrel shoots. Did you lap it prior to installation?
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Now that the initial testing was done with the cast bullets, it was time to try out the .25 cal Disco Double with my favourite pellet, the 25.4 gr. JSB King.... I left the gun tuned the way it was at the end of the bullet testing, which was about 60 FPE.... I expected I would have to reduce the hammer spring preload with going to half the weight pellet, and that was exactly the case.... Here are the results.... The green line is the way the gun was set for the last test (also a green line) with the bullets.... You can see that it pretty much started on the top of the bell-curve, I had to turn the RVA out 2-3 more turns to move the shot string over....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleJSBPellets_zpsde3f2d8a.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleJSBPellets_zpsde3f2d8a.jpg.html)
Here is summary of the averages for the shot strings in the above graph....
Maximum: 1162 fps (76.2 FPE) for 7 shots at 0.65 FPE/CI (all supersonic)
4 turns out on RVA: 1097 fps (67.8 FPE) for 12 shots at 0.77 FPE/CI (just subsonic)
5 turns in on velocity screw: 991 fps (55.4 FPE) for 18 shots at 1.09 FPE/CI
6 turns in: 922 fps (47.9 FPE) for 19 shots at 1.03 FPE/CI
There are a few useful shots missing on the last string, backing the RVA out to 4 turns out like in the other strings (it was at 3) would have dropped the velocity slighty, added shots, and increased the efficiency.... Tunes in between any of these can be obtained by using adjustments finer than a full turn, of course.... One thing that I was very pleased about was how tight the groups were with the Kings.... I'm used to seeing ragged holes at 20' even when I'm not taking my time and just shooting through the Chrony, but here is what I was getting for 8 shots.... Yep, that's just a 1/4" hole!....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleJSB_zpse568f9b1.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleJSB_zpse568f9b1.jpg.html)
When I was doing the Chrony work with the bullets I was using up some unsized bullets I had that had very uneven bases, bent by the sprue cutter.... The groups were unacceptable, even for Chrony work inside at 20'....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleSolid_zps69a65b93.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleSolid_zps69a65b93.jpg.html)
When I was done with the Chrony testing I switched to the last batch of .25 ACP bullets I cast (some 46.4 gr Hollowpoints) and ran an 8-shot magazine through to see if they were any better....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleHP_zps082b0231.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleHP_zps082b0231.jpg.html)
While not as tight as the Kings, this group is consistent with what I usually see with good pellets while doing my Chrony work inside, and usually means I can expect to be able to cover the group with a dime at 25 yards when I move outside.... It certainly proved to me, once again, how important it is to have as perfect and square a base as possible on a bullet.... It just makes sense, it causes the same problems as a bad crown on the muzzle, right?....
One of the things that amazed me during the testing of the JSB Kings was how much I had to restrict the flow to get the velocities in the sub-1000 fps range.... At 5 turns in on the velocity adjusting screw, the nose of the bolt is blocking 0.16" of the 0.25" long barrel port.... leaving just half of a 3/16" hole available for the air to flow through to drive the pellet.... That is basically the same area as a stock 0.134" Crosman barrel port.... AMAZING !!!
Bob
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I lapped it with JB Bore Paste (100 strokes full length; 100 more tapering, more at the breech) and then polished it 50 strokes with Bore Bright prior to installation.... I pretty much do that to every barrel I make.... First time it's off the gun, or if accuracy falls off, I give it 10-20 strokes with Bore Bright again....
Bob
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That's what I figured. ;)
If you keep those Kings right around 1020 fps you should see .5" groups at 75 yards.
That is using lubed pellets though..........dry (straight from the tin) my groups opened up.
So the Max useable length on an Mrod magazine is .4"?
Or is it .39?
I can make a Spitzer .390" long and have .150" shank length for bore stability - plus with the base obturating to bore diameter I don't see an issue with yaw down the bore line.
What it weighs we wont know until I've punched one out and put it on the scale.
I love how you've added yet ANOTHER tuneable dimension to your gun with the bolt probe depth adjuster!
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Tom, I thought understood what you meant, but I wanted to see the photo to make sure.... I don't see how that could work in my application.... You would have to load the pellet whatever length the "streamlined" portion was ahead of the barrel port in order for the full diameter portion to obscure the port.... That extra wasted volume behind the pellet would surely take away from any theoretical advantage to turning the flow smoothly around the corner.... Your setup I'm sure works great when positioned as you would at full power and with a non-retracting bolt.... but with a bolt where you seat the pellet and then retract it to the firing position, you would be loading the pellet further forward than necessary or desireable.... unless I'm missing something?....
Bob
Bob, I started coming around to your argument this morning, thinking dead air space all the time might not be good. I am there now. Regards, Tom
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A ,25 cal MRod magazine measures 0.48" where the middle of the nose of a pellet would be (eg. on a Predator), but the recess for the nose is only about 5/32" wide and radiused.... If the nose of the pellet is wider than 5/32", it won't go into the recess at all, and then the length available is 0.45".... If the bullet is too tight a fit, and it cocks sideways even a little, it can prevent the magazine from indexing.... My ACP Hollowpoints are 0.436" and the nose doesn't drop into the recess and they work fine.... The RN soild of the same bullet is 0.471" and it fits in the magazine but jams because it doesn't drop quite deep enough into the recess.... I made my new bullets (which have a 0.130" Meplat) 0.455" long and I'm hoping they work OK.... I may have to shave the top of the mold 0.005" if they don't....
Bob
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I threaded the muzzle for the Hatsan air stripper and installed the carbon fibre shroud and stripper.... The accuracy seems unchanged inside at 20', but it's pretty hard to distinguish small changes at such close range.... I tried some Daystate Rangemaster 36 gr. pellets as well, which were pretty dismal in my Hatsan, and they shot nearly as tight as the JSBs, so it looks like the warning on the box about being intended for unchoked barrels may have merit.... I tested them at 950 fps (72 FPE) and they can be tuned both up and down from there.... so definitely worth invetigating....
Bob
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.455" long shows a weight of 51 grains. Launched at 895 fps (90 ft lbs) it retains 77 ft lbs and drops 9.8" @ 100 yards.
Of course that length will be lighter due to the base punch.
Can anybody figure out the cubic volume of a cone?
Its .190" in diameter at the base and travels at a 35* angle until point intersection.
If I know the cubic volume of the base punch I will know how much weight to deduct from the Border Barrels design model.
Where are you getting this melt & pour soap? Sounds like I might want to have some on hand.
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V=Pi(r^2)h/3
Surface area= Pi(r^2)+Pi*rsqrt(r^2+h^2)
Hope that helps
Bill
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It does, except offhand I don't know the value of 'h'.
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For 35* per side, "h" is 0.135", ie if the cone is 0.190" at the base and 0.135" tall, the angle at the top will be 70*.... I get a volume of 0.00127 cu.in.... Lead weighs 0.409 lb..cu.in. adn there is 7000 gr. per lb., so that works out to 3.65 grains....
Bob
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Thanks Bob!
:)
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Today I tried several different tunes for the JSB Kings around the 55 FPE level.... The plan was to try adjusting the hammer preload weaker (and drop the fill and refill pressures) while opening up the barrel port by backing out the velocity adjusting screw.... I wasn't fussy about getting exactly the same velocities with each tune, I recorded all the shots within a 4% ES (~40 fps), and all the shots were between 965 fps and 1018, so the strings were within about 15 fps for the peak velocity.... I backed off the hammer spring preload a turn, dropped the fill pressure 200 psi, and opened up the barrel port to keep roughly the same velocity for each string.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/25DiscoDoubleAdjustments_zps2d6f5cbd.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/25DiscoDoubleAdjustments_zps2d6f5cbd.jpg.html)
The numbers on the legend are the number of turns in from maximum power on the bolt travel (barrel port restriction) and the hammer spring preload, measured from the lock nut to the end of the adjuster (bigger distances mean less preload).... The -5T and 0.358" curve started at 3000 psi, and the last string shot, (-2T and 0.568") started at only 2000 psi.... I know it's a bit hard to see, with all the lines on top of each other, and the curves look silly with the drastically expanded vertical scale.... but here are my conslusions....
1. There was little to choose from for the efficiency.... All the strings were between 1.02 - 1.10 FPE/CI, with no real trend apparent.... The differences may have been more due to some strings being a few fps faster, or missing a shot or two on the front end of the string because the starting pressure I used wasn't quite high enough....
2. As the pressure range dropped and I compensated by opening up the porting to keep the same power, the shot strings got shorter and more curved.... The range of pressure between the ends decreased.... Once again, it is apparent that wide open ports can develop good power at low pressures, but the price you pay is a low shot count.... You can equate big ports to a hot cam in a racing engine.... More power for a given pressure, but a narrow power band....
3. All these tunes used about 50 psi per shot from the 250 cc Disco Double reservoir.... in fact the range was narrow, between 48-52 psi per shot.... Each vertical line on the graph therefore represents about 50 psi.... With the ports wide open, I was able to get 1000 fps (55 FPE) from only 1700 psi, which is pretty amazing, IMO....
4. The longest shot string was at about 2800 psi fill pressure, and ran 18 shots, but it was missing 1-2 shots off the front end of the string, and peaked at over 57 FPE.... I feel that with some fine tuning, I can achieve 20 shots at 55 FPE average from a fill, within a 4% ES.... I can already get 13 shots within a 2% ES, and 17 shots within a 3% ES, averaging closer to 56 FPE with the Kings....
While the purpose of this gun was to achieve a higher power level using cast bullets, I'm very pleased with the flexibility demonstrated to shoot JSB Kings at 1000 fps with a good shot count.... and once again I was provided with the opportunity to learn more about PCP tuning....
Bob
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Fantastic information (as usual!).
I've learned more about tuning a PCP from reading your information and test procedures than just about all other sources combined.
My Double Tube for my Challenger is 22" long vs the standard 18" which gives me roughly 285 cc's.
With my hammer preload screwed all the way out (off of the hammer spring but still attached to the adjuster body) I get an average of 1023 fps from a 3k psi fill.
Starting with 2900 psi, here's a 10 shot string:
998
1010
996
1023
1022
1030
1033
1038
1040
1041
Ending at 2550 psi
My guns powerband using cast bullets is from 2600 psi down to 1900 psi.
For pellets I try to keep my pressure between 3000 - 2500 or it fires the JSB'S too fast and I lose accuracy.
If I trade my 10.6# hammer spring for a lighter one it will be more pellet friendly but I will lose my horsepower for cast bullets.
I still think the Discovery valve design is the best platform for building on! Especially with a Double Tube kit.
Sorry Mrods.................
I have to give it to you Bob - you've built the most tuneable non regulated powerhouse I've seen with that breech of yours on that Disco Double!!!
:)
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My new Boattail bullet mold arrived a couple of days ago and I cast some bullets yesterday.... The new .300 cal bullets came out at 70.4 gr. and they function perfectly in the modded MRod magazines....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/IMG_3897_zps5a3bbf0b.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/IMG_3897_zps5a3bbf0b.jpg.html)
Here is what they look like....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/IMG_3881_zps834e3469.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/IMG_3881_zps834e3469.jpg.html)
Since these bullets are a lot heavier than the 50 gr. JSB pellets the gun was built for, I maxed out the hammer spring preload and the velocity adjuster and ran a string.... It peaked at 114 FPE and averaged 837 fps (110 FPE) for 9 shots.... so a little bit more hammer strike is required to get the maximum from one 7-shot clip.... I'm hoping to fix that issue by replacing the valve poppet with one made from PEEK which is a harder material and takes less energy to break loose from the seat.... I shot a couple of other strings with the velocity adjuster run in a bit (which restricts the barrel port with the nose of the bolt), and here are the test results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleBoattails_zpsedd43787.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleBoattails_zpsedd43787.jpg.html)
The last string was two full clips (14 shots) averaging 86 FPE at an efficiency of 1.11 FPE/CI, which is the same energy as I got with the 50 gr. pellets when the gun was set for 14 shots at fractionally better efficiency.... The way I see it, the best use for these bullets will be with the gun adjusted for a single clip at maximum power.... The bullets were all going into ragged holes between 3/8" and 1/2" OD during Chrony testing, which is pretty good for cast bullets.... Proper accuracy testing will have to wait until the spring, however....
Bob
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Great work and excellent information as usual Bob....
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This is a duplicate of the post in the Machine Shop Gate.... All Geeks please respond over there !!!
Well you knew I had to do it !!! .... My .30 cal Disco Double is one of the best documented guns I have, and with the new 70 gr. bullets it's now limited out on performance due to insufficient hammer strike.... or rather it WAS, until today when I made a new poppet out of PEEK for it.... All I can say is WOW !!!
Before I tore the gun apart, I made some measurements of valve lift, using an O-ring on the rear cocking shaft.... This is an easy procedure, you slide the O-ring up against the adjusting screw on the RVA, cock the gun, fire it, and measure the gap.... Voila!, instant measurement of how far the valve opened.... I set the preload to maximum (as near coil bind as will safely cock), opened the bolt stop to maximum (this gun has the ability to choke off the barrel port with the bolt nose), loaded a 50 gr. JSB, and checked the valve lift at 2800 psi and again at 2000.... I did 2 shots to confirm the measurement, and I was pleased that they were the same within 0.001" or so.... I then repeated the test with no pellet loaded (open bore), and then I moved the bolt nose forward with the adjuster to close off the barrel port, loaded a pellet to block the bore even more, and did another set of lift measurements.... These three conditions change the flow around the head of the poppet, from "normal" to as much flow as possible (barrel at atmospheric with no pellet), to virtually no flow where the pressure on both sides of the poppet is nearly the launch pressure (the velocity drops to about 200 fps, you can see the pellet arc through the air to the backstop).... This gives us a way to somewhat quantify the aerodynamic drag trying to close the poppet, relative to the major closing force, which is the air pressure acting on the 5/32" valve stem.... Anyway, I then tore apart the gun and made a new poppet out of PEEK, reassembled it, and repeated the tests.... Here are the lift measurements....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/PEEKPoppetLift_zpse1de81da.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/PEEKPoppetLift_zpse1de81da.jpg.html)
As you can see, the PEEK valve had about a third more lift at 2800 psi, with the same hammer strike, so it is obviously a LOT easier to unstick from the seat.... There can no longer be ANY doubt of that.... The lift of the PEEK valve at 2000 psi was limited by the physical room between the face of the hammer and the back of the valve, which is 0.162".... You can also see that compared to the "normal" case of firing a pellet, with no load (and therefore a bigger pressure difference across the head of the poppet) the lift is slightly less.... while with the barrel nearly blocked (and therefore very little pressure difference across the head of the poppet) the lift is slightly greater.... That difference in lift is due to the aerodynamic drag across the head of the poppet, which shows up as a pressure difference between the valve housing and the exhaust port, which in turn increases the closing force during the valve cycle.... The differences are smaller with the PEEK valve, likely because the head is a smaller OD.... Here are the two poppets....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/IMG_3902_zpsdba636a1.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/IMG_3902_zpsdba636a1.jpg.html)
You wll notice that the Disco poppet, which has seen maybe 500-1000 pellets during testing, is pretty badly pounded.... While it is not extruded like the one in my Hayabusa was (which had a larger throat), it would appear that 3000 psi on a 1/4" throat is really more than it should see.... The ID of the Disco valve, BTW, was bored out to 5/8" ID so there is lots of room for flow around the head.... When I made the new PEEK poppet, I made the OD the same size as the valve spring.... The stem is made from 5/32" drill rod with the end threaded 8-32 for 1/4" of length and then the stem is slimmed behind that to 7/64", the same as I did on the Disco stem.... The PEEK valve head is drilled and tapped 8-32 and glued onto the stem with medium viscosity CA glue before final finishing.... Thanks, Lloyd, for the idea of threading it on for extra strength !!! ....
Of course my testing didn't finish with just measuring the lift, I had to see if the new PEEK valve increased the performance.... Well, the first thing I noticed was that the gun was louder and a lot thirstier for air.... My SCUBA tank was down to 2800 psi, but that was enough to drive a 50 gr. JSB at 1033 fps (119 FPE) compared to a previous best of 1011.... The 70 gr. Boattail, which I could only get to 852 fps yesterday screamed across the Chrony at 918 fpr (131 FPE).... I'm sure those numbers will increase further at 3000 psi.... I then started backing off the preload, with the pressure in the SCUBA tank gradually dropping, and it was obvious that even with the heavy, 70 gr. bullets, the gun, rather than being limited by hammer strike, was operating on the velocity plateau for the pressure available.... I had to back the preload down 5 turns before the velocity started to drop significantly.... At 6 turns out, the velocity pretty much matched the way the gun shot with the Disco poppet at maximum preload, starting at 830 fps and climbing gradually.... There is one problem, however.... The gun is suffering from a LOT of air robbing hammer bounce.... It appears that the PEEK valve is so easy to open that the returning hammer is burping it a couple of times, even at velocities where I was getting a decent string yesterday....
My ShoeBox is currently chugging away topping up my SCUBA tank, so further testing will have to wait.... I'm guessing that I'll have to use a shorter, stiffer hammer spring to get rid of virtually all of the preload to eliminate the hammer bounce.... I know that something will work, because my Hayabusa doesn't have this issue, nor does Sean's .30 cal QB.... It looks like a whole new learning curve is required to find the best combinations to work with the new PEEK valve.... There can be no question, however, that by using this material for the poppet (or seat) you can immediately reduce the hammer strike required for a given pressure and valve throat size.... Can lighter hammers be in my future?.... certainly the gun just got a whole lot easier to cock....
Bob
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I had a chance tonight to find out how the .30 cal Disco Double responds to hammer spring preload with the new PEEK valve.... Previously there wasn't any point as the gun couldn't reach its maximum potential as the hammer strike was the limiting factor, not the porting.... With the new valve, and tethering the gun at 3000 psi, I could now explore the guns power curve.... Here it is, plotted for both 50 gr. pellets and 70 gr. bullets....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleHammerSettings_zps443bcea0.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleHammerSettings_zps443bcea0.jpg.html)
You can see the same velocity plateau as the gun maxes out as you get on a regulated PCP, where additional hammer strike just wastes air.... The "knee" of the curve is where the plateau starts, and there is no point in running more hammer spring preload than that.... This occurs at about 4 turns out from coil bind with the pellets and 3 turns out with the bullets.... Going past that point gains only about 20 fps and doubles the amount of air used.... Even at that setting, the first shot will basically be the fastest, normal unregulated bell-curves start just below the knee of the curve.... at maybe about 5 turns out with the bullets and 6 turns out with the pellets....
The absolute maximum values obtained with this gun were 117 FPE with the 50 gr. pellets and 135 FPE with the 70 gr. bullets....
Bob
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I was a bit worried about the excessive air consumption with the PEEK valve due to air-wasting hammer bounce.... The only string I recorded yesterday was 6 shots, 855-864-833 with the 70 gr. bullets, and that used 1100 psi for a horrible efficiency of 0.59 FPE/CI.... Something obviously had to be done !!!
As a cure, I decided to try a shorter, stiffer hammer spring to get rid of the significant preload with the QB spring.... Lloyd was the first to notice an efficiency increase from eliminating the preload, and both Sean and I have observed it too, so it seemed like a logical place to start.... I had to shorten a 2.5" x 0.059" wire spring that I had to 2.0" by cutting off 4 coils.... The spring was a snug fit in the hammer (so it would bind on compression), so I had to drill it out one size as well, to 3/8" ID.... I was still able to use the 7/32" spring guide / rear cocking rod.... I had the preload set for 5 turns out with the QB spring, and to my surprise, with the new spring, that put me right at zero preload but no slack as well, exactly where I wanted to start.... The first shot across the Chrony was at 1000 fps with the Daystate 50 gr. pellets, so I knew I was close....
The new stiffer spring is a LOT more sensitive to preload adjustment, of course, at 1 and 2 turns in the velocity maxed out at 1021 fps, which showed me that zero preload was right where the plateau started.... Since I wanted to be on the knee of the power curve, that meant I would have a slight amount of free play in the spring, which I hoped would eliminate, or at least severely curtail, hammer bounce.... At 1/2 turn out the velocity was 972 fps, at 1 turn out it was 956, 1.5 out it was 935, and at 2 turns out is was 904 fps, so I chose 1 turn out for my first string.... My SCUBA tank was down to 2980 psi, so the first string started there, and I got 7 shots (1 clip) within just a 7 fps range (0.7% ES), averaging 100 FPE, and with an efficiency of 0.96 FPE/CI.... WOW ! I've never seen anything that flat before unless regulated.... Maybe this PEEK valve DOES produce tighter strings?....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleNewSpring_zpse1daef68.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleNewSpring_zpse1daef68.jpg.html)
I backed the preload down another turn, and cranked the velocity adjuster in 2 turns (which does very little) and shot another string.... This time I got 13 shots, starting from 2920 psi, 904-940-906, averaging 94 FPE at an efficiency of 1.09 FPE/CI.... I cranked the velocity restrictor in one more turn and repeated the string, starting at 2900.... I got 14 shots, 878-897-864, averaging 86 FPE at 1.10 FPE/CI, and the string should have started 1 shot earlier if I had a full 3000 psi in the tank.... Even so, this 2-clip string spanned less than a 4% ES, and over 14 shots will be a bit tighter with a 3000 psi fill.... The string stayed within a 4% ES down to 1860 psi, which is 100 psi lower than with a similar tune using the Disco poppet.... The PEEK poppet was truly showing its stuff !!!
I'm very pleased with the new PEEK valve, now that I have the proper hammer spring to compliment it.... The valve is easier to knock off the seat, reducing the hammer energy required to get this gun to full power from over 1.12 FPE (over, because I never quite got there with the Disco poppet) to 0.90 FPE.... or putting it another way, the valve gets a third more lift from a 1.12 FPE hammer strike.... The PEEK valve opens so easily, however, that it is prone to being reopened by hammer bounce.... I cured that by using a shorter, stiffer spring, that instead of preload, had a bit of free space for the spring to rattle around when uncocked.... This DRASTICALLY reduced the report of the gun from reduced air wastage.... I had thought previously that this was the case, but today's experiment proved that it can and does work.... The only downside is that the new spring is harder to cock.... The ultimate solution would be more hammer travel and going back to a QB spring without preload, but adding that much hammer travel is not an easy thing to do when I've already increased the travel from 0.58" to 0.75".... One thing I know for sure, there will be more PEEK poppets in my future, particularly on high pressure, large throat valves, where driving them open is difficult anyway....
Bob
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I finally got around to fitting my new .357 cal barrel this week.... Sean Pero and I designed a new airgun specific barrel to run anything from roundball to about 160 gr. bullets.... It is 0.357" groove, 0.350" land, with a 26" twist, with 6 narrow lands, and is hammer forged in CrMoly with a 1/2" OD.... The one I got is 28" long.... I had a chambering reamer I had made for my LW 9mm barrel, and it worked just fine.... I made the chamber long enough to work with the 132 gr. Lee RF bullets I had, but in fact even the 154 gr. will chamber without too much effort.... When you chamber a JSB .35 cal Exact, the head is most of the way engaged into the lead and the skirt stops just short of the beginning of the leade, which starts about 1/10" past the barrel port.... The bolt is sealed with a 9mm x 11mm x 1mm O-ring in a groove in the barrel.... It's a very skinny O-ring but seals well and so far seems to be standing up just fine.... The only thing that is a no-no is pushing the pellet out backwards into the breech, the skirt cuts the O-ring.... I found that out when I was checking what the rifling engagement was like....
The valve in the gun is the same PEEK valve I recently made for it, and it has a 1/4" throat and 0.219" ports, which are on the small side for this caliber, so I really didn't know what to expect for power.... The gun was still set up for the .300 cal I recently tested, so the first couple of shots were at that setting, and went across the Chrony at about 920 fps, which was a pleasant surprise, at nearly 150 FPE.... I topped up my SCUBA tank during dinner and this evening got down to some serious testing.... I filled the gun to 3000 psi, cranked the hammer spring preload to just shy of coil bind, and tested all the various 9mm/.357 ammo I have.... Here are the results.....
68 gr. Roundball: 999 fps (149 FPE)
78 gr. JSB Exact: 961 fps (159 FPE
90 gr. Air Venturi HP: 925 fps (171 FPE)
117 gr. Air Venturi RN: 848 fps (187 FPE)
126 gr. Air Venturi RN: 817 fps (187 FPE)
132 gr. Lee RF: 808 fps (192 FPE)
154 gr. Lee RN: 742 fps (188 FPE)
In every case, the second shot was a lot slower, and 2 shots dropped the pressure to 2260 psi, which works out to an ear-splitting 0.40 FPE/CI for (non)efficiency.... Well, the gun was a bear to cock like that, but at least I had enough hammer strike to get everything out of the restricted porting that was possible.... It was pretty apparent that with the porting the gun has, the 78 gr. JSB pellets, which were the original design intention for this gun, were just about perfect.... so the rest of the testing was done with them.... I shot strings at gradually reducing hammer spring preload, recording all shots with 4% of the peak velocity for that string.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/35DiscoDoubleStrings_zps9344a063.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/35DiscoDoubleStrings_zps9344a063.jpg.html)
At Max. preload the second shot was down more than 4%, and at 1 turn out the velocity was only down 2 fps, but the gun did manage a 2nd shot within 4% ES.... The velocity was obvious plateaued at the 3000 psi fill pressure, confirming that I had enough hammer spring to get everything out of the gun.... It got 3 shots at 2 turns out, and 4 shots at 3 turns out, with the first two nearly identical, and at that point the efficiency had improved to a still dismal 0.65 FPE/CI.... At 4 turns out the spring has no preload but also no slack when the gun is not cocked, and the gun was now showing signs of a normal shot string, delivering 6 shots with 4% ES at 0.78 FPE/CI.... At 5 turns out, the velocity had dropped quite a bit, and the first two shots were more than 4% below the peak, but the string had 9 shots with a 4% ES, starting from 2800 psi, at an efficiency of 0.96 FPE/CI, not bad for a big-bore.... I turned the preload back in 1/2 turn for the final test, and got 7 shots with 4% ES, the first 6 were within just 17 fps (2% ES) at an efficiency of 0.85 FPE/CI, with the string ending at 1940 psi.... The 7 shots averaged 884 fps (135 FPE), which I'm pretty darned happy with....
This barrel was kind of an afterthought for this gun, the porting was optimized for .25 cal bullets and .30 cal pellets, weighing about 50 gr.... I'm pretty sure that with larger porting the efficiency would increase significantly, and it would probably be possible to tune for a string in the mid 900s with the JSB pellets (ie 150-160 FPE) with decent efficiency.... Anyway, when you consider the gun started out as a humble Disco, and it's still using a stock valve with the ports just opened up to 0.219" and a PEEK poppet.... I think it's pretty impressive to get 6 times the original FPE with a usuable 7 shot string....
Bob
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Bob, that thing is just nasty. ;D When are you going to chase down a moose with it? ;D ;D ;D
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Great information and practical demonstration as usual Bob.
The 7-shot string seems a nice compromise between power, ES and count. I'm reading someone who is working on tuning up the Rainstorm and reducing the ES at the same time as well - and his early results (with minimal changes) are v. promising. Wish you'd turn your eye to that gun. I'd almost donate one to you to see your results ;D
That 28" barrel must be quite a sight on the Disco. Seems that you swapped it in pretty handily onto the Disco. What do you think it would take to put one of those barrels (maybe a 25) on an Evanix Rainstorm?
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Backing the preload out just a whisker from the 4.5T setting might squeek out an 8 shot string starting from 3000 psi within a 4% ES in the 850-890 fps range.... My Disco Double has a repeater breech (single shot loading in .35 cal) that I made myself, and it has a 1/2" ID the same as the breech on a .25 cal MRod.... I'm not at all familiar with the Rainstorm, but if the barrel OD is 1/2" it would slide right in, if it's larger, the barrel may be available with a larger OD, or it could be sleeved to fit.... I know Sean is pretty busy right now, but I'm sure he could do pretty much anything you want....
I've thought about working on a Rainstorm at some point, but funds and time are always the problem.... It certainly can't happen this winter, and during the summer I don't have the time because of the Motel....
Bob
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I put the .300 cal barrel back on today because I had more testing to complete.... I never worked out a useable tune with the PEEK valve, new hammer spring, and the 70 gr. Bob's Boattails.... So, here is the data, along with that for the JSB 50 gr. (Daystate) pellets....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleNewStrings_zps7385bc70.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleNewStrings_zps7385bc70.jpg.html)
In a similar state of tune, the heavier, cast bullets produce about 20 FPE more energy than the pellets, but at about 80 fps lower velocity.... To do that, they require one more turn of preload on the hammer spring to compensate for the greater mass.... The shot strings are shorter because you are extracting more energy per shot from almost exactly the same pressure drop.... In both cases, for the "black" strings, the end pressure was just over 1800 psi, starting from 3000, which is a fairly wide range to stay within a 4% ES.... That seems to be a characteristic of the PEEK valve, extending the useful pressure range, and hence shot count.... Here are the tabulated results:
50 gr. JSB pellets:
7 shots @ 100 FPE @ 0.93 FPE/CI
13 shots @ 94 FPE @ 1.02 FPE/CI
14 shots @ 86 FPE @ 1.01 FPE/CI
70 gr. Bob's Boattails:
4 shots @ 131 FPE @ 0.51 FPE/CI
6 shots @ 119 FPE @ 0.76 FPE/CI
9 shots @ 110 FPE @ 0.85 FPE/CI
11 shots @ 104 FPE @ 0.93 FPE/CI
The valve in this gun, which has a 1/4" throat, is plenty for the 90-100 FPE range for the JSB pellets, but it's struggling a bit with the 70 gr. boattails, just as it is with the .357 cal barrel.... It simply can't flow enough air to develop over 100 FPE with good efficiency.... I understand that Sean is planning to fix that by sending me a new valve to play with.... My problem will be to figure out how to make the transfer port large enough to handle the extra flow....
Bob
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Bob,
Looks like it took some work to get the peek valve figured out. I know the peek valve is easier to open, but does it make the valve poppet any lighter?
So the short, heavy spring ended up being the most efficient?
How many additional foot pounds do you think the peek valve was able to extract from the DD? You are getting incredible power from a valve with only a .25" throat. Excellent.
Lloyd
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The PEEK valve is not really allowing me to get more power, technically.... It's allowing the hammer to open the valve without having to use so heavy a spring I can't cock the gun.... *LOL*.... I never tried the .357 barrel with the Disco poppet, but on the .300 cal, the best I got was 113 FPE, but with the PEEK poppet I got 135 FPE, nearly 20% more, and that was using 70 gr. bullets.... I have no doubt the difference would have been larger with heavier ammo....
Yes, getting 192 FPE from a 1/4" throat is pretty impressive, but the efficiency is dismal at that power (0.4 FPE/CI).... Unfortunately, even set up for a proper shot string, the efficiency isn't that great (about 0.9 FPE/CI).... Not only are the ports being sonically choked, they are just plain too small for that bore, or even for the .30 cal at anything over 100 FPE.... The short heavy spring helped the effiiency quite a bit, I was getting a lot of hammer bounce with the QB spring and the PEEK valve.... just too easy to crack, I guess.... Maybe be careful what you wish for?.... *LOL*....
Bob
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Bob,
Sorry to keep pestering you with questions, but this is very intriguing. So if I am understanding this correctly, the peek valve, being much easier to open, allows lighter (compared to the usual Delrin poppets) spring forces to open the valve. And this allows you to max out the flow in the system without it seeming like you are hammering the valve to death. And now the new maximum is higher than the old because you can drive the valve harder. But then you have to change the spring methodology to avoid hammer bounce. Wow! Quite a journey but that is really good as it does open up some very new possibilities, as you and Sean have already show with the other peek applications.
The dismal efficiency you refer to when driving the valve really hard (with the barrel area being.... gulp.... over twice the throat area!!!!).... I assume the calculator shows that the valve is staying open well past half way down the barrel and the low efficiency isn't being caused by something else?
Thanks a bunch,
Lloyd
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You summary of how the PEEK valve changes things is correct.... As to the dismal efficiency (when cranked to the max.), it's no worse than my DAQ .308 Exile was when I first got it, at 0.38 FPE/CI for only 3 shots with a 90-95 fps (rapidly dropping) spread and using 400 psi per shot....
As you know, Lloyd, your spreadsheet has no way to differentiate between dwell and efficiency, they go hand in hand.... The further the pellet is down the barrel, the lower the FPE/CI, and vice-versa.... Just using the ratio of HPA released to barrel volume, my calculations show that the valve is open for 76% of the barrel length.... The port to barrel area ratio in this gun (38%) is only slightly worse than on a stock .22 cal Disco (42%), so we're not in uncharted territory.... However, getting 192 FPE from it would be like trying to get (over) 71 FPE from a .22 cal Disco through the stock 0.140" transfer port.... admittedly with 3000 psi and a 50 gr. bullet....
Bob
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I've been watching this thread with great interest. I've ordered a 30 cal barrel from Sean. Now I NEED a 357 and some bullet molds ;D From an engineering perspective, Do you think there is any efficiency to be gained by going the smoothtwist way and only rifling the last 4 inches? Would doing this minimize damage during loading as I assume that the pellet would be well centered by the time it hit the rifling?
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I don't understand how the smooth twist idea works, as the rifling is about a 16-18" twist, but only results in a 100" or slower twist rate, so the pellet must be skidding across the rifling.... When they start winning all the benchrest contests instead of conventionally rifled barrels, I'll likely pay more attention....
Bob
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I shouldn't have mentioned smoothtwist as it implies other concepts and baggage that I know nothing about....
My real questions are: Do you think there is any efficiency to be gained by only rifling the last 4 inches? Would doing this minimize damage during loading as I assume that the pellet would be well centered by the time it hit the rifling? It seems to me that this might be a good way to go when using a liner as the edges of the rifling are not as sharp.
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For the same reasons I stated, I can't imagine why you would want to do that.... Instead of the pellet being engaged into the rifling before it starts it's journey, and being accelerated in rotation at the same time as longitudinally, it will be travelling at high speed with no rotation before hitting the rifling, and while it will pick up "some" spin at that point, if will also be stripped of it's outer diameter, sizing it essentially to the land diameter.... If you look up photos of recovered pellets from smooth twist barrels (essentially what you are describing) you will see that they show virtually no residual rifling marks.... While that smoother surface may increase the Ballistics Coefficient by decreasing the drag, the resulting very slow spin rate (it has been measured as low as 1 turn in 156" - 13 feet).... would never work with a cast bullet.... Without the inherent drag stabiizaton of a diabolo (waisted, or shuttlecock) pellet, the bullet would be prone to tumbling with such a low spin rate....
IMO, the proper chamber length is one where the nose of the projectile is engaged in the tapered leade between the smooth chamber and the full depth rifling....
Bob
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Thanks Bob,
Now I get it. They made a pellet only smooth bore barrel with a choke that imparts a small amount of spin.
John
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Correct, good description of it.... When they choke it, they do so over a mandrel with the rifling on it....
Bob
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I've been working on my marauder valve in preparation for a 30 cal barrel and probably a 357 in the near future. The thru flow is 0.360 and the transfer port is currently 0.188. I can go as big as I want on the transfer port in this configuration, but at some point it becomes to easy to damage the pellet or bullet. I'm considering using 2 transfer ports and a slightly longer bolt probe. I'm planning on going regulated with about 115CC of plenum. My 500cc fill pressure will be rated at 3625 PSI. I'd like to solicit any thoughts as to this configuration and the optimum port sizes and regulated pressure.
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Not sure how having a .360 "through flow" (which I assume you mean the valve throat?) helps when the valve exhaust port is so tiny as shown in that photo.... I realize that with the MRod valve body having the exhaust port so close behind the throat increasing its diameter helps the angle of the flow.... but the ultimate answer is to move the seat forward to allow a bigger exhaust port.... Likewise, once the flow is choked down to 3/16" by that exhaust port, I see little point in using huge (or multiple) barrel ports as all they do in increase the volume between the valve and the pellet, dropping the pressure.... I don't go larger than 75-80% of the bore with the width of the barrel port to avoid pellet damage, but you can make a longer, oblong shaped port....
If you look down the page on this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=61527.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=61527.0) .... to a post by SeanMP with photos of the 2-piece MRod valve he made, you can see just how big the ports can be by redesigning the valve.... It is possible to get to .30 cal boresize porting straight through, even the barrel can achieve that by using an oblong port (say 0.24" wide by 0.36" long).... but in reality, just going to a ~75% boresize port of 7/32" (0.219") will allow well over 100 FPE performance in .30 cal.... For a .357, then you would ideally want to go larger (17/64" or 0.266" would be a good choice).... If you want to do both, then I would use the larger size, 0.266", which gives you 75% porting and allows a round barrel port in .357 and you don't have to go ridiculously oblong in the .30 cal to have equivalent area.... a barrel port of 0.22" x 0.31" could be made to work with the 0.266" transfer port very easily.... The throat required, assuming a 1/8" stem, would be a minimum of 19/64", but I would go right to 5/16" (0.312") like Sean did in that valve.... Those port sizes are larger than what I used in the Disco Double in this thread, and it achieved over 100 FPE with pellets and 130 FPE with 70 gr. bullets at 3000 psi.... With the bullets, at 2000 psi, I achieved about 108 FPE, so with the bigger porting you should be able to do a bit better, and I would think that would be a good place to aim at with a regulated .30 cal....
Bob
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Thanks Bob,
The valve throat is 0.360 and the poppet diameter is 0.400 in delrin. I still need to run some numbers on this set up, but it appears to be reasonable. I eliminated the valve spring in order to use the spring guide diameter as the new valve throat. I thought I'd mess with Peek after I get it functioning.
So, In order to accommodate both the 357 and 30 cal and trying to take your advice, I'm going to open the exhaust and transfer ports to 0.266 and just choke it at the barrel port on the 30 cal to 0.219 and use the full 0.266 on the 357.
I guess my next problem is going to be trying to get sufficient hammer energy at a reasonable cocking force?
John
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BTW,
What do you use for a transfer port? I've been using rubber tubing in my small calibers, but I would assume as the energy levels increase I need to be a little more careful in my material selection.
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I ran up to .375 transfer sleeves by supporting them with the breech and air tube; they can't expend very much, and the teflon I made them from is about .020 longer so that they are compressed by the breech clamp screws. With a throat that big, I suggest using PEEK for the valve heads as it is more able to tolerate the stress and opens easier for a given hammer hit.
cheers,
Douglas
http://www.gatewaytoairguns.org/GTA/index.php?action=media;sa=media;in=2116;preview (http://www.gatewaytoairguns.org/GTA/index.php?action=media;sa=media;in=2116;preview)
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You can cheat a little bit on the barrel port on the .30 cal to take advantage of the 0.266" transfer port.... Make the barrel port 7/32" wide, but 5/16" long at the boreline.... You do that by first drilling it 7/32" (0.219") and then using a 7/32" mill, move the back of the port back 0.023" to line up with the back of the 0.266" transfer port.... Do the same at the front, but angle the mill about 30* forward so that the port is only 0.266" long at the transfer port face, but 0.312" long at the boreline.... The actual angle you use will depend on the amount of meat you have between the transfer port flat on the barrel and the boreline.... A little careful work with a Dremel will blend the sides of the barrel port to the round transfer port, without making the port at the barrel any wider than 0.219".... Here is a drawing for a similar port in .25 cal....
(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/25OblongPort_zps678624e7.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/25OblongPort_zps678624e7.jpg.html)
In that case, the transfer port was 1/4" (boresize) and the barrel port was 3/16" x 5/16" to get the same area....
Bob
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Thanks Gentlemen.
I'll see if I can implement this in the short term. I'm anxiously awaiting my 30 cal barrel from SeanMP and not sure what the barrel port will actually be, I'm trying to get everything else ready.
I think a better long term solution for the marauder might be to make a new breech, move the loading port forward and use a thru bolt design, thus eliminating the barrel port. This would also allow for correcting the poi shift - breech flexing problem as well. If it was a side level it would allow a larger range of hammer springs. With a little careful design it would allow for future larger calibers. Anybody interested in working on a design and sharing a small production run? (I saw LLoyd-ss has already made a very cool marauder side lever).
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If you asked Sean for an oblong port to match to a given diameter transfer port, I'm sure that's what you'll get.... or could get....
By "through-bolt" are you talking a rear tank like a Condor?.... Otherwise how will you eliminate the barrel port?.... Also, then you are faced with the problem of the restriction on flow caused by the bolt itself, which obvioulsy has to be smaller than boresize....
You may be underestimating what you call "a little careful design", if it were that easy, it would have already been done, and in several versions.... JMO....
Bob
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What I'm imagining is something like a 0.625 dia hollow bolt with a hole in the side that lines up with the valve exhaust port when the bolt is locked into place. You would put the bullet directly into the barrel. Here's a quick drawing of the bolt.
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I just don't get it, sorry.... How do you "put the bullet directly into the barrel?.... If the bolt is larger than the bullet, it can't push on it, right?.... The hole for the air would have to be smaller than the bullet as I see it.... I also don't understand how that bolt would align the bullet with the bore if it's 5/6" OD.... The other problem is the hugely increased volume between the transfer port and the base of the bullet, which drops the pressure during the all-critical first part of the shot.... I'm probably just not understanding what you are trying to achieve, perhaps if you showed the bullet and bore in relationship to the bolt and the transfer port?....
Bob
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My goals are to make the breech more rigid, possibly add side lever to aid in cocking larger springs, maximize air flow, and make it easier to change caliber. Currently I'm shooting single shot as I have found that the magazine tends to damage the skirts and open up my groups at 75 yards (.25 cal and smaller).The barrel could be allowed to extend into the loading area, with the top half cut away, to make a single shot tray. if you wanted to use the magazine a caliber specific probe could be screwed into the bolt. I don't see much increase in air volume between the valve and the barrel with this proposed design, less than 1.5 cc.
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While 1.5 cc doesn't seem like much.... it's t least double the normal volume between the valve seat and the pellet for a .30 cal.... Let's assume the volume only doubles, from 0.75 cc to 1.5 cc.... In an MRod with a 20" barrel, in .30 cal, shooting 90 FPE at 3000 psi, doubling the volume between the valve and the pellet costs you 4 FPE with no other changes....
Bob
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It would seem to me that the increase in flow all the way to the bullet must offset the added volume, to a point. It seems like the basic understanding is that the energy is limited by the smallest restriction in the system, but a water hose gets a huge velocity increase from a significant restriction right at the nozzle. So if you ran a 0.5" flow all the way to a .357" barrel would it force a velocity increase right where you want it? Or would you be better off with just .357" flow or something even smaller?
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I'm not sure if the same dynamics apply with HPA as with water, which is incompressible, for your garden hose analogy.... HPA acts somewhat in between what we think of as a gas and a liquid, and the higher the pressure the more it acts as a liquid.... On the other hand, we are pushing the pellet near the speed of sound (with beyond it being possible but ill advised for other reasons)....
Just as having ports too small can cause "sonic choking" of the flow, making them larger than boresize could, presumably reduce the drag of the air moving through the passages between the valve and the pellet, and increase the force at the pellet as a result.... The velocity of that flow is basically irrelevant, because once the air molecules reach the pellet, only the force they can exert accelerates the pellet, and that is proportional to the pressure.... As you make the ports larger, however, you drop that pressure because the air moving out of the valve has to expand to fill that space before it gets to the pellet.... That is where I got that 4 FPE loss I mentioned above.... The data comes from an Internal Ballistics spreadsheet put together by Lloyd Sikes that he graciously gave me, and has proven an excellent tool for understanding the dynamics of what happens inside a PCP when you change things.... The losses from too large a transfer port volume are pretty significant....
Where the "optimum" port size is, is still open for debate.... I can tell you that I have seen increases in FPE right up to bore-size porting, and I have not tried to do beyond that as I can see no reason to from the current knowledge bank we have.... If it possible that further gains may be made, but it's difficult enough just to get there, let alone beyond....
Bob
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Thanks Gentlemen.
I'll see if I can implement this in the short term. I'm anxiously awaiting my 30 cal barrel from SeanMP and not sure what the barrel port will actually be, I'm trying to get everything else ready.
I think a better long term solution for the marauder might be to make a new breech, move the loading port forward and use a thru bolt design, thus eliminating the barrel port. This would also allow for correcting the poi shift - breech flexing problem as well. If it was a side level it would allow a larger range of hammer springs. With a little careful design it would allow for future larger calibers. Anybody interested in working on a design and sharing a small production run? (I saw LLoyd-ss has already made a very cool marauder side lever).
Lol...Here is an example of it pays to snoop around once in awhile...never know who's talking about you ;D
My standard port for the 30cal is an oblong port .225"x.300 giving an effective area of .055sqin. Thats within 15% or so of the effective bore or TP of .290ID. Thats about all you can squeek out of a 3/8OD. You could get away with .300ID but the walls would then be .035" and thats getting fairly intricate to cut a teflon seal half that dimension.
My usual TP is a simple barrel with a step on each end to hold a small ring of teflon. the metal body is .020 shorter than the total height and the rings are sized to give .010" of interference
John I can definitely save you some time here. That delrin will not survive a .360 throat. Its going to extrude and lock the valve. You may as well start with PEEK and avoid the need to to back track. I absolutely assure you it will fail at any reasonable pressure
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After a busy Summer in the Motel, I finally got a chance to get back into the shop.... I dragged out the Disco Double, which had been leaking, and pulled the valve because I knew all the other O-rings weren't leaking.... While it was out, I drilled out the throat from 0.250" to 0.266" to make it about 10% larger than the rest of the ports.... While that doesn't tend to increase the power, it does tend to increase the efficiency, and that small change I could do without disturbing the OD of the seat, so that the valve wouldn't be any harder to open at 3000 psi.... I put new O-rings on the valve, reassembled the gun, and that indeed was the source of the leak.... I tested all the barrels, and there was basically no increase in velocity, but the efficiency went up 5-10%, so the experiment was not only worth it, but confirmed my previous experiments with slightly oversized throats.... The exhaust, transfer, and barrel ports are 0.219", and the equivalent throat area (ID minus stem) is 0.241", which is 10% oversize in diameter, and about 20% in area....
During the testing of each caliber I used one pellet and one bullet.... In .250 cal I used the 25 gr. JSB King and my 51 gr. Bob's Boattail.... For the .300 cal I used the Daystate 50 gr. pellet and my 70 gr. BBT.... In the .357 cal I used the JSB 78 gr. pellet and my 127 gr. Boattail.... I tried different preload setting with each until I found the one that would give me a starting velocity just within 4% of the peak for that pellet/bullet.... When I was finished, I decided to put my "Best Tune" picks all on one graph, so that we could see how the different calibers compare, and here it is....
(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/DiscoDoubleTunes_zpsef65df88.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/DiscoDoubleTunes_zpsef65df88.jpg.html)
The dashed lines are pellets, and the solid lines are bullets.... black for .25 cal, blue for .30, and red for .35.... All strings except the .25 cal with the JSB Kings (and the .357 with bullets) were shot with the barrel port wide open, and the hammer spring preload adjusted so that the first shot at 3000 psi was just within a 4% ES of the peak for that string.... Therefore, they represent the most powerful and longest string I can get with a 4% ES starting at 3000 psi.... Had I done that for the .25 cal Kings, the velocities would have been approaching 1100 fps (the gun can drive a King at over 1200 fps, WFO), so I cranked in the adjuster that prevents the flat nosed (probeless) bolt from being withdrawn clear of the transfer port a full 5 turns (7 is fully closed).... That dropped the velocity into the 950-1000 fps range, and I know that the Kings are still accurate there, so it seemed like a good choice.... and easy to change my mind on the velocity by small adjustments on the bolt restrictor.... I ended up with 26 shots (over 3 magazines) at over 55 FPE average from the 250 cc reservoir, which is over 1.20 FPE/CI, stellar efficiency at that power, IMO.... The other exception is the 127 gr. bullet in .357 cal. where I got 3 shots within a 3% ES, without regard to the efficiency, which turned out to be 0.62 FPE/CI.... not bad for 170 FPE....
The other 4 strings all ran from 0.91 to 1.06 FPE/CI.... I should mention that if I want to tune those 13-14 shot strings for a single magazine with the minimum possible ES, by increasing the preload about 1 turn I can get less than a 2% ES for 1 mag. at significantly more FPE.... This is always an option to trade shot count for more power and a tighter ES if necessary.... Of course if you want to tune for slightly less power by turning in the bolt restrictor slightly, then those 13-14 shot strings can easily be stretched to two full magazines as well.... Anyway, all in all, I'm very pleased with the final results.... The gun turned out to be good with pellets and bullets in all three calibers.... It spans the range in power from Ground Squirrels to Deer and Hogs, and everything in between, depending on choice of caliber and ammo.... Pretty good for what started life as a Disco....
Bob
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I knew the barrel Sean and I designed for this gun was good.... but I had NO idea how good.... Tim @ Mac 1 just won the Extreme Bench Rest contest with his USFT, rebarreled with one made by Mike at TJs.... in a 1/8" wall CF sleeve.... shooting 45 gr. JSBs.... WAY TO GO, TIM !!!
Bob