GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on March 14, 2013, 06:37:40 PM
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Well, let me start by saying I don't have a Marauder.... I did, however, purchase a .25 cal valve a couple of years ago out of curiousity.... Today I decided to see how big I could hog it out.... and here are the results....
The first thing I did was remove the velocity adjusting screw and glue in a brass 8-32 screw tightened fully (partly into the port) and cut and grind it off flush on the outside.... I figured if I was going to enlarge the ports, there was no point in having it adjustable.... I did a lot of measuring, and decided that I could enlarge the exhaust port to 3/16", which is 75% of a .25 cal barrel, and should be plenty big enough to make big power.... I needed the valve throat at least that much area, so I drilled it out to 15/64" (0.234").... which when you subtract the 0.125" stem diameter is the equivalent of a 0.198" hole, about 11% more area than the 3/16" exhaust port.... That should be plenty, and doesn't enlarge the seat, so the valve shouldn't be any harder to crack open.... I then ran a 7/16" end mill down the inside, followed by a 1/2", to 1.95" from the end, just shy of the valve seat.... I then ground the end of a 1/2" drill to fit over the seat area and used it to finish the 1/2" ID hole down to when it JUST removed the anodizing on the botom of the valve around the seat area.... I then milled out the exhaust port, first to 5/32" to remove the end of the brass screw, then to 3/16", and enlarged the transfer port recess to 5/16" so that a 5/16" OD Teflon transfer port can be used.... Here are the photos....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_3192_zpsea5d59d3.jpg)
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_3194_zpsf458c506.jpg)
As you can see above, I also modified the inlet plug to allow more air into the valve.... I milled two 1/4" slots in the sides at 90* to the screwdriver slot, just removing the threads.... I marked the end of the valve where those flats tightened up, and plunged a 1/4" end mill down to remove the thread as far down as I could reach with the mill (but staying clear of the 4-40 breech screw holes), tightened the end cap in, and then countersunk the end of the holes and smoothed them over with a Dremel.... Here is a photo of the assembled valve....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_3196_zpsdb3426b0.jpg)
I also drilled the middle hole in the end plug to 17/64", and shortened the shoulder around the spring seat to 0.120" and reduced the OD inboard of the threads to 7/16", to unshroud the bottom of the new outer slots.... The total inlet area is now more than double what it was originally, and more than 3X the exit area.... In addition, the much larger ID virtually completely unshrouds the head of the poppet, removing any previous resistance to flow through the relatively narrow gap there.... The new ports are 78% larger than stock, and of course the barrel port would have to be enlarged to 3/16" as well, and a 3/16" ID transfer port fitted.... The bolt probe might also need some work....
There are a couple of areas where Crosman left VERY little material, and when you are hogging out an MRod valve, if you go too far, you will ruin it.... The two 4-40 screws that hold down the breech are 0.58" apart to the inside of the screws, so 0.50" is the largest you can go with the ID of the valve and still leave enough material around them.... The transfer port is VERY close to the back of the inside of the valve (thanks, Rescue35?), and if you enlarge the exhaust port too much, you will cut through behind the raised valve seat.... That will also happen if you cut too deep when boring the valve out to 1/2" ID.... If you try and radius the front edge of the exhaust port, where it goes around the corner into the valve throat, you can easily destroy the seat.... All I did was smooth the sides where the 3/16" vertical port meets the 15/64" horizontal throat, and JUST broke the edge on the forward side.... Even so, there is little material remaining on the top edge of the seat....
Why did I go to all this trouble when I don't own an MRod?.... Good question.... I did it so that I can understand what you guys are going through trying to free up the flow on an MRod.... Crosman left so little material in the areas mentioned, that you can actually get bigger ports in a Disco valve.... Having said that, the ports I have achieved could be done reliably and if a guy set up for it, at relatively low cost.... I see no reason why this shouldn't allow an MRod to produce enough FPE to use 50 gr. cast bullets like those from the RCBS mold for the .25 auto, or the 50 gr. Mr. HollowPoints.... I checked both of those, and they both fit in the .25 cal MRod magazine and it still rotates freely.... The 54 gr. Mr. HollowPoint will fit inside but drags, and the 58 gr. is simply too long.... I'm thinking that given what Lloyd and I achieved with a .25 cal Disco, it should be possible to get very close to 100 FPE at 3000 psi with 50 gr. bullets (OK, maybe 90ish FPE with a 20" barrel) and a valve like this in an MRod.... Who's going to be first to do it (or has it already been done)?....
Bob
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Ship it, I'll try it.
:)
Thanks for the experimentation Bob!!!!
SAFE & Happy Shooting!!!!
Dave
8)
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^^^ What he said !
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Very funny, guys!....
Bob
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U better just hook up ur 4500 psi tank directly to your rifle.. :) U might get 5 shots with your stock air tube... :)
Gene
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I got 6 shots within a 5% ES from 3000 psi down to 1900, averaging ~95 FPE, with those bullets in my Disco.... should be nearly 10 shots on an MRod at similar power.... just based on the reservoir volume.... I could be wrong, of course....
Bob
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I snuck a little information into this thread about using 50 gr. cast bullets in an MRod magazine.... I'm surprised nobody jumped on that discussion....
Bob
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Nope, missed that. My eyes were glazed over and watering from the 95fpe number.
:o
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Well that's part of the trick to get that kind of FPE.... heavy bullets.... I was surprised when I found that the 50 gr. (actually 53 gr.) RCBS, the 46 gr. hollowppint version, and the 50 gr. Mr. Hollowpoints would all function in an MRod magazine.... I don't think I've ever read of anyone trying that before.... Here is what happened in my Disco with different weights....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/25DiscoPelletWeight_zps57e0ebb5.jpg)
Note that the FPE was still rising at 65 gr.... I eventually pushed a 50 gr. bullet to 1002 fps (112 FPE) at 3000 psi during testing.... The ports were only slightly larger than what I was able to get in the MRod valve, and the Disco has a 24" barrrel, not 20".... but I'm thinking somewhere in the 90's for FPE should be possible (maxed out) with this valve....
Of course the power would have to be backed down a bit to get a usuable shot string.... but it would sure be interesting to see what you could get for an 8-shot (1 clip) string with a 3000 psi (maybe even 3200?) fill.... Makes me wish I had an MRod to try it in.... :(
BTW, I see Hunter's Supply sell a 53 gr. round nose.... it looks like the RCBS.... $28.00 per hundred, $93.00 for 500.... You can cast for less, but that would be a good alternative for those than don't.... http://www.hunters-supply.com/shop/index.php?cPath=27 (http://www.hunters-supply.com/shop/index.php?cPath=27)
Bob
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If you have knowledge of a valve change in the new Marauder, please share that.... They may have moved the trigger, but unless they took that opportunity to redesign the valve (which would surprise me) then nothing would change.... If you were OK with moving the port back in the valve, main tube, breech, and barrel (not sure how you'd do that) then you could use a bigger port.... The parts you showed are more than likely the result of somebody boring the exhaust port out and ruining a valve.... That would certainly be a way to fix that problem, however.... The seat could also be made from metal (OD still sealed with an O-ring) and use a stock MRod poppet, just machine some of the back of the valve (there is enough material, I checked into this idea already) to get the valve travel back.... That would also increase the hammer travel, which is not a bad thing....
So, it is possible to increase the porting larger than I did, but only if you replace the seat in the valve, moving it forward a bit.... or move the ports back.... You have to ask yourself if that is really necessary when the heaviest bullets that will fit the magazine are about 50 gr., though....
Bob
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Just tagging to read later. Looks great!
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hey Bob,
Now go and cut down the poppet head diameter a wee bit closer to the seat diameter. That goes in direction of boring the ID of the main valve body out, and since you can't go over .500, might as well take the poppet diameter down...:)
One of Jim Gaska's magazine covers, perhaps taken further than he does usually would lengthen the allowable bullet selection. I may try this; I have a 24-1/2" BSA barrel for my 2563..:) and a 500cc tank. I am a wee bit tired of hearing about, 'get a sumatra iff you want big power, mrods can't do it'...lol
cheers,
Douglas
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might as well take the poppet diameter down
Not quite sure why?.... The area around the poppet is already about 4 times the throat area with the 0.5" valve ID.... I guess you might benefit from a slight streamlining, but since the spring is the same OD as the stock poppet, do you really think there is much to be gained?.... The choke point is still the 3/16" exhaust, transfer, and barrel ports....
If you figure you can get over 100 FPE from a quarterbore MRod, then you might need to go heavier than 50 gr.... otherwise, why bother?....
Bob
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i shot the rcbcs 50 grain casts out of my mrod was curious had the trajectory of a lobbed softball lol slowpitch leaugue it would be mice to get some more oooomph considering how accurate they are
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might as well take the poppet diameter down
Not quite sure why?.... The area around the poppet is already about 4 times the throat area with the 0.5" valve ID.... I guess you might benefit from a slight streamlining, but since the spring is the same OD as the stock poppet, do you really think there is much to be gained?.... The choke point is still the 3/16" exhaust, transfer, and barrel ports....
If you figure you can get over 100 FPE from a quarterbore MRod, then you might need to go heavier than 50 gr.... otherwise, why bother?....
Bob
Well Bob, how about cutting the poppet down instead of the slightly more difficult opening the valve...if yours has gotten 4x the area, do you really need all that...can you get 2.5x by just cutting the head?
cheers,
Douglas
nevermind, I'll just get a big one...:)
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how about cutting the poppet down instead of the slightly more difficult opening the valve
The OD of the head has virtually nothing to do with the force closing the valve (that's mostly the stem diam.) and nothing to do with the force to crack the valve.... which is the sealing diameter....Changing the head OD or the valve ID is just about area for flow, and IF the area is relatively small, the associated drag through that space, IMO....
As I said, the spring is the same OD as the poppet head anyway, the best you could do is a slight tapering towards the throat....
Bob
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Thanks for thinking it through with me Bob...going to have some fun modifying drills...:)
cheers,
Douglas
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I just ran the 53 gr. RN Lyman through the Border Barrels Twist Calculator.... With an 18" twist, the Stability Factor is 1.6 at Mach 1, and 2.6 at 500 fps.... The 46 gr. Hollowpoint version works out to 1.7 at Mach 1 and 2.1 at 500 fps.... The 50 gr. Hr. HollowPoint is 1.5 to 1.9 at subsonic velocities.... These are the three cast bullets that will fit in an MRod magazine, so it looks like conventional airgun twists should be perfect for them.... A stability factor of 1.5 - 2.0 is "optimum" and anything over about 4.0 is "overstablized", while 1.0 or less is unstable....
Bob
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Bob, I just saw this thread 'cause it was going on when I was sick and moving (yes, both at the same time, yuck.)
I ran into the same situation when trying to boost the power for the .308 M-rod bottle gun I just did. Like you, and everyone else, it seems, when I first saw that big, fat M-rod valve, I thought, wow, plenty of room to open it up. But with no extra metal behind the valve seat, and the two 4-40 breech screws crowding the hole thru the valve, and the restriction of the spring retainer, I finally gave up on modifying the valve and made my own from scratch. It wouldn't be necessary for smaller calibers, including maybe the .308, but I wanted to do it anyway.
What you have done is good for over 120 fpe, but of course, I needed more power, LOL. :P
I didn't take a lot of pictures, but I ended up moving the valve seat forward to get a .437 O.D. transfer port, sealed with o-rings and with a .301 hole. I opened the front end of the valve up as big as I could and made a spider to capture the front end of the valve spring. The main restriction in the system is the nose of the flow-thru bolt. The breech is now attached to the tube with four diagonal 4-40 SHCS that are threaded into the air tube, not the valve.
I didn't have the gun long enough to really play with the tune, but hopefully, I will soon.
Lloyd-ss
.328 valve throat, .312 exhaust port
(http://i226.photobucket.com/albums/dd79/loyd500/Grumpys%20Mrod/DSCN2794_zps1147ae3f.jpg)
The front of the spider isn't too pretty with all the hand work done late at night.
(http://i226.photobucket.com/albums/dd79/loyd500/Grumpys%20Mrod/DSCN2795_zpsda3c2fea.jpg)
.308 M-rod bolt. The .238 hole thru the tip of the bolt will be the choke point, and I don't know if it will be a problem or not.
(http://i226.photobucket.com/albums/dd79/loyd500/Grumpys%20Mrod/flowthrubolt_zps3a397b3f.jpg)
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Looks good, Lloyd.... I know you can make a bigger custom valve, I just wanted to see what the limits are on modding a stock one.... If it will reach 100 FPE in .30 cal that would be great!....
Bob
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Excellent Lloyd.. So the one in the picture is your own design? Again can u explain how you hold your custom valve in the air tube?
Great work
Gene
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Bob,
I think with the mods you have made to the M-rod valve and porting you should be able to get 100fpe in .30 cal, don't you?
Two different approaches to the same problem.
Gene,
Yes, the valve is my design, but it is fairly conventional. The valve itself is still held in place with the three 10-32 socket head screws just like the stock valve, but the attachment of the breech to the tube is what makes the difference.
So as not to hijack Bob's thread, I put some more info on this thread.
http://www.gatewaytoairguns.org/GTA/index.php?topic=38581.40 (http://www.gatewaytoairguns.org/GTA/index.php?topic=38581.40)
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Hijack away, Lloyd.... not a problem, my friend.... It's all about trying to make an MRod breathe better....
Bob
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:'(
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Thought I'd present y'all with a power update. I got some Hunters Supply 53 gr, .251 bullets. At less than 700 fps they did not fly well...so in went a de-sleeved 22 cal valve with .160 port and sleeve on a .165 barrel port. I got 800 fps, and at 50 yards shot a 5-shot dime-sized group. Was dancin' in the streets. Throat is .250"...I suspect a bit more area between stem and port makes it work better.
Next up, taking a stock sleeve to .169" and the exhaust port to the same, maybe .172" The spot where the OE O-rings ride will be paper thin at that size, but I think I'll see a few more FPE out of it. Also planned is a stem seal. I plan to shorten the rear of the valve about 1.2mm and adding a 2mm thick plate screwed on with an o-ring stuck in between in a liddle relief volume, likely countersunk, held on with countersunk itsy bitsy screws. There is enough flow past the stem to blow moly-loaded 2C45 Krytox all over the face of the hammer( added moly powder to the Krytox and it thickens a bit ).
cheers,
Douglas
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I think with the mods you have made to the M-rod valve and porting you should be able to get 100fpe in .30 cal, don't you?
As an update, Lloyd, I would think it would be VERY close to that figure shooting 50 gr. JSB .30 cal pellets.... My .30 cal Disco Double has a 3/16" valve port and hit 97 FPE with a 3/16" transfer port and 102 FPE with a 0.219" transfer port, both at 3000 psi with the 46 gr. JSBs.... I'm guessing the MRod valve with 0.188" ports will be within spitting distance of 100 FPE at 3000 psi in .30 cal....
Bob
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I think with the mods you have made to the M-rod valve and porting you should be able to get 100fpe in .30 cal, don't you?
As an update, Lloyd, I would think it would be VERY close to that figure shooting 50 gr. JSB .30 cal pellets.... My .30 cal Disco Double has a 3/16" valve port and hit 97 FPE with a 3/16" transfer port and 102 FPE with a 0.219" transfer port, both at 3000 psi with the 46 gr. JSBs.... I'm guessing the MRod valve with 0.188" ports will be within spitting distance of 100 FPE at 3000 psi in .30 cal....
Bob
That tears it...I'm going big...lol But seriously, doesn't speed in that regime take a bit more energy just to accelerate that much air in the barrel? I think I'd add mass to slow it down to 900 fps. All in the name of efficiency, on a rifle that is getting more shots than game spottings on a hunt.
cheers,
Douglas
cheers,
Douglas
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Well, the pellet choices in .30 cal are two weights of JSB, 46.3 gr. and 50.2 gr.... They are both the same length (0.38"), the heavier one has a larger waist.... We won't know how the BC changes with velocity until we test them, but they are a bit heavier than a scaled up JSB King, with approximately the same SD as a 25.4 gr. JSB Monster .22 cal.... which certainly still have a great BC in the 900s.... While it's true that there is more air to accelerate in a .30 cal barrel, there is also a bigger area for the air to push on to accelerate the pellet (and that air)....
The actual numbers that can be achieved by a .30 cal MRod will probably be heavily influenced by the length of barrel used.... If you stick to the stock 20" barrel, it could be tough to hit 100 FPE.... with a 25-26" barrel, not quite so tough.... Either way, actually tuning the gun for 100 FPE is probably not going to be great, the first shot will likely be the fastest.... To get a decent shot string I'm thinking more in the 80 FPE range would be a more likely result.... That's what I'm hoping for in my .30 cal Disco Double....
Bob
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I'm looking forward to seeing what I can get out of my newly acquired 25 marauder.
It sounds like the bottle marauder would be perfect for these power mods as well as a longer barrel. Where can one get a 25" barrel that isn't a 257 groove?
Todd
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I'm looking forward to seeing what I can get out of my newly acquired 25 marauder.
It sounds like the bottle marauder would be perfect for these power mods as well as a longer barrel. Where can one get a 25" barrel that isn't a 257 groove?
Todd
I don't know about 25", but mine is a BSA I got from England, and it is only 24.5" long. But I have to say that .257 stuff is much more common, I may have to get another and barrel it thusly...lol
cheers,
Douglas
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.25 Auto liners from TJs are .250 groove and .243 land, which is correct for .25 cal pellets.... and bullets sized to 0.250" of course.... They are available in any length, and in 1/2" OD which will fit an MRod (and 7/16" to fit a Disco).... IIRC, he charges more per inch for 29" and longer.... They are a 14" twist....
Bob
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Bob,
Any thoghts on 1/4" OD transfer sleeving with OD near the 3/16" ID? Or is it required to cut the barrel and valve to run 5/16"? I assume a drill can be taken to the breech itself fo clear the bigger stuff, or did I miss something?
cheers,
Douglas
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Don't have an MRod, remember, illegal in Canada... I've only punched out a .25 cal MRod valve as big as I could.... I don't know about the transfer port on an MRod, I've never seen one.... When I go to a 3/16" ID I usually go to a 5/16" OD on the Disco.... I mill a new flat on the valve and barrel that is 5/16" diameter to get a sealing surface and drill the breech and the main tube to 5/16" to clear it.... Using Teflon rod for the transfer port still works with a 5/16" OD up to a 7/32" ID.... Over that I go to 3/8" OD.... The largest I have gone with a 1/4" OD transfer port is 0.166" (the same as a poly tube port).... Thinner wall than that they tend to collapse.... You MIGHT get away with 11/64 (0.172") in a 1/4" Teflon port if you get the length perfect.... If you drill the steel transfer port sleeve in a Disco out to 0.169" it tends to buckle where the rubber seal sits.... sounds like the MRod might be similar?....
Bob
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Since I just purchased another .25 Mrod, and since you cannot own an MRod, I again say send it to me or sell it to me and I'll do some real world numbers on it.
:)
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I don't know about the Disco, never seen one's insides either...LOL Motorhead has some tubing with .180 ID he's sending. Seems quite a thin wall, and like you mention, length will be critical...I hope I wind up with enough for several tries. That said, I can certainly get the barrel and valve spot faced 5/16, and deill the tube and breech the same. I confess I will be tempted to do one in Al or steel and seal it with square o-rings...and the 3/16 port is certainly attractive. Much more area than the .160 I am now running. Something will have to be done...:)
cheers,
Douglas
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Since I just purchased another .25 Mrod, and since you cannot own an MRod, I again say send it to me or sell it to me and I'll do some real world numbers on it.
:)
he did call it first...:)
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hey-Hey!!!,
With a .180 transfer sleeve, exhaust port and barrel port I got 19 shots between 790-810-790 on 750 psi of tank pressure drop. With the smaller port, the speed dropped off much earlier; it took higher pressure to maintain the speed. Peak is now 10 fps faster...but the curve is pretty manageable...:) going to have to see about a 3/16 porting and 5/16 Teflon transfer sleeve as soon as I can manage it...:) Pressure at start was 2k85 and I ended at 2k1 psi. Turning it up for use at 3k2 fill ought to deliver some more energy...lol...again with the 2-clip tune
cheers,
Douglas
.88 FPE/ci...:)
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19 shots between 790-810-790
What pellets?....
Bob
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19 shots between 790-810-790
What pellets?....
Bob
The 53 gr that look to be from an RCBS mold. The ones from Hunters Supply that just suffered a price increase of nearly 20%.
cheers,
Douglas
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So about 75 FPE....
Bob
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So about 75 FPE....
Bob
I used 75.5 as the average. Is a velocity curve quite similar to your green DD .30 curve.
cheers,
Douglas
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So who supplies power junkies without valve modding skills a nice upgraded unit?
I am itching to try something like this.
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So who supplies power junkies without valve modding skills a nice upgraded unit?
I am itching to try something like this.
The full job would take a bit more than just the valve. Up to what I have done can so far is just the valve( with the exception of a .165 barrel port on the 24" BSA barrel )...so perhaps see Lloyd.
cheers,
Douglas
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What do you guys think about discarding the inlet plug all together and just drilling a 1/8"
hole all the way through the valve body so you could compress the spring and slide in a 1/8" pin to retain the spring at the correct distance? One could grind a flat side in the middle of the pin for the spring to stay in place?
Like this.
(http://i40.tinypic.com/21boscp.jpg)
Edit: I might have to cut in another oring groove on the backside of the pin to keep air in?
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You would definitely have to cut another O-ring groove as drawn.... unless you drill the space between the existing O-ring groove and the end of the valve (1/8") and use a thin pin.... A 1/16" steel pin would be strong enough.... but you still have to figure out how to locate the spring on it....
How much area do you figure you need on the inlet side of the valve?.... I already have 3 times the outlet area.... If you were dealing with a regulator in the way and needed more plenum volume I could see doing it, maybe....
Bob
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It looks like there is enough room for an oring groove after the pin and before the breech screws. I might be able to make a stand off that the pin slides through for the spring to sit on, like your idea but I think it would want to try to rotate around the pin and bind up on the side of the valve under pressure? edit: (or use a longer spring.)
I am going to be running a Huub vented regulator into an opened up gauge block, into the valve pushing a .22 pellet and probably eventually with an air tube extension. I am not really a numbers guy so I was just going for big and easy. ;D
Looking at what you and LLoyd did, this looked easier to me and seemed like it would flow well with more (maybe not more) plenum space?.
edit again, One could make a spacer that fits on the valve head to hold the spring to makeup the difference in length?
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Just use a longer spring....
Bob
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Joel,
I can't escape thinking the spring will jump out around the pin and valve body. Also, the bolts that hold the reciever to the air tube are too close together to allow you to bore the ID so large. With the Marauder valve a big flow impediment seems to be the sharp turn to the exhaust port right behind the seat. If you can move the seat forward by ~3/16" you can andle the port by 20 degrees from its vertical, OE configuration. This seems to help a great deal.
For your 22 cal, I'd suggest a .234" throat, and an angled .165 exhaust, a .165 poly transfer tube, and a .165 port in the barrel. If you want to get really nuts, a slightly bigger throat, and a 3/16" exhaust to go along with an oblong ( a slot in the barrel )barrel port will enable some serious power and require heavy slugs. Without going past .165 round barrel port, you should be able to achieve 60 FPE with the heaviest pellets...and at reasonable efficiency to deliver a full magazine worth of low-velocity-spread shots.
cheers,
Douglas
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Thanks Bob..
Douglas, That drawing was not to scale or anything and I had no intentions of opening it up bigger than the breech screw depth (1/2") if even that. Just trying to get rid of the inlet plug restriction easily and give you big bore guys some other ideas. Thanks for the advice.. ;)
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Thanks Bob..
Douglas, That drawing was not to scale or anything and I had no intentions of opening it up bigger than the breech screw depth (1/2") if even that. Just trying to get rid of the inlet plug restriction easily and give you big bore guys some other ideas. Thanks for the advice.. ;)
Whilst playing with a stock config, bored valve I re-installed a stock valve body cap and got no drop in performance while running in the 85 FPE neighborhood. I still modify the cap, but I can't excape the conclusion that it matters very little, and efforts should be spent elsewhere.
cheers,
Douglas
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Thank you sir, that is helpful!! My goals for this .22 are modest fpe and more about the flat string, shot count, and education. Then go nuts on the next one... 8)