GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: darkcharisma on March 03, 2019, 02:49:34 AM
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Hi Bob and everyone that is interested.
I have a Gauntlet in .25 that is currently making 60fpe and can push to 64fpe with JSB 34 grain. I am interested in finding out if a build for .224 caliber is worth while. I am even contemplating .172 build. Here are the parts I currently have (not installed)
TJ .224 1/14 twist 25 Inches long.
Cothran Valve with .250 exhaust.
Walther .172 28inch barrel 1/9 twist
I want to push a 55gr slugs towards 990fps, is this gun capable with the limited 25cc plenum plus the cothran valve? I am asking a double FPE here. What do you think Bob? Everyone chime in if you have some experiences and recommendations...I can go with a lighter bullet also.
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First update: Gauntlet+cothran with 7/8 tube but 1/2 inch longer than oem tube. probably same 25cc volume due to the bigger and longer valve than oem valve. pictures on post #30
.250 caliber tested
1300psi=855fps/34gr-55fpe
1300psi=756fps/46gr-58fpe
1700psi=880fps/34gr-58fpe
1700psi=788fps/46gr-63fpe
2000psi=924fps/34gr-64fpe
2000psi=835fps/46gr-71fpe
2200psi=950fps/34gr-68fpe
2200psi=950fps/32.8gr vk slugs=66fpe
2200psi=936fps/34gr NSA slugs=66fpe
2200psi=915fps/36gr NSA slugs=67fpe
2700psi=1020fps/34gr-79fpe
2700psi=910fps /46gr-85fpe
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modded gauntlet valve. 25 cal
1300psi=800fps/34gr-48fpe
2000psi=909fps/34gr-62fpe
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.22 caliber tested
2700psi=1215fps/14.3gr= 47
2700psi=990fps /28.6gr=62fpe
2700psi=845fps /42.9gr=69fpe
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Second Update; Marauder 85cc, slugs
2200psi=925fps/39gr=74fpe (17 shots; 3.5ksi>2.2ksi)
2200psi=785fps/55gr=75fpe
2300psi=938fps/39gr
2300psi=800fps/55gr
2700psi=1009fps/39gr (enlarged barrel port, 10 shots)
2900psi=999fps/39gr=86fpe (12 shots; 4ksi>2.8ksi))
2900psi=850fps/55gr=88fpe
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I put a 24" .224 LW barrel in to a BSA Hornet and got 100 fpe with 48 grain 225420 bullets at 200 bar. Barrel size porting. IMO 990 fps with 55 grainers is asking a lot from a 25" barrel, you need a rather high pressure to be able do that. Not to mention that 55 grain bullets are likely to need more twist than 14". Bullets in the 40 grain area should do the trick, check Bob's cast bullet sheet for ideas.
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I don’t own one but I think it’s close enough to the QB guns that I can share . I would get rid or the regulator and get it as close to free flowing as possible from bottle to plenum . High power and regulators make the job that much harder , throw in a small plenum and the job gets even harder. As RKR mentioned a bullet in 40 grain would be a little easier to get to the 990fps . I’ll be watching this one . I’ve done a Cothran QB in .257 and it maxes out at 160 Fpe with a 30” barrel at 3000psi.
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I figure the 25"/25cc is asking alot even with Cothran valve. Regulated at 2k even makes it harder to reach 120fpe. But at the same time I have never play with the Cothran valve either.
yes I can settle for a 40 grains bullet. What are the proven accurate bullet designs for this weight? I know NOE has a 225-39grains but I have not seen the MOA results.
Currently I cannot go above 2000psi due to the stock tube. Any recommendation for 3000psi tubes? I may have to fit the TJ barrel and find out where my current velocity is with the 25cc plenum. Everything is set up and ready just needs to bore out the receiver.
Thanks guys I will update soon
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I would go with a longer barrel at 28" or longer and a faster twist rate.
You bottle are alredy rated for 3000psi so I do not see the need to replace it.
But I feel that 25cc of plenium is very small so I would run the bottle unregulated and opening up the ports from the bottle to the valve to .240 and after that you would have a plenium of 220cc+.
If you want to keep it regulated, you will have to make a longer plenum tube and buy a 4500psi bottle...
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It will be a challenge to get to 100 FPE at 3000 psi with a 25" barrel but it can be done.... You certainly won't do it at 2000 psi, not even close.... Trying for 120 FPE with those specs will not happen.... you would probably need at least 3600 psi to do that.... If you do go regulated, you will need at least 1 cc per FPE of plenum....
Also, a 14" twist will not work with a bullet the length of most 55 gr. ones.... Concentrate on bullets the length of the Arsenal Bowman 47 gr. or less.... In fact, that could be the ideal bullet for your build, at 950 fps it would be 94 FPE, which should be achievable....
Do NOT run the Gauntlet tube at 3000 psi, but you know that anyways.... You could use a CrMoly tube of 7/8" OD x 0.065" wall for your build.... The ID is the same as a Disco, so you could use a Cothran valve for a Disco.... then open up the passages through the tank block to 1/4" to allow the bottle to act as part of the plenum.... Don Cothran could probably make you a tube if you send him your old one as a sample.... Opening the passages through the tank block may be more of a challenge, depending on how much material there is....
Bob
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It will be a challenge to get to 100 FPE at 3000 psi with a 25" barrel but it can be done.... You certainly won't do it at 2000 psi, not even close.... Trying for 120 FPE with those specs will not happen.... you would probably need at least 3600 psi to do that.... If you do go regulated, you will need at least 1 cc per FPE of plenum....
Also, a 14" twist will not work with a bullet the length of most 55 gr. ones.... Concentrate on bullets the length of the Arsenal Bowman 47 gr. or less.... In fact, that could be the ideal bullet for your build, at 950 fps it would be 94 FPE, which should be achievable....
Do NOT run the Gauntlet tube at 3000 psi, but you know that anyways.... You could use a CrMoly tube of 7/8" OD x 0.065" wall for your build....
Bob
Is it not rated for 3000psi? does it have a burst disc for 2000psi?
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I assumed that since the Gauntlet is QB based it might not be.... However, upon re-reading the OPs post, he is starting from a .25 cal, which indeed uses a setpoint higher than what a 1.8K burst disc would allow, and has extra screws holding the valve.... I have never seen a Gauntlet, nor done the safety calculations, so all we can do is trust Umarex that they have done their homework, and that the gun is safe for 1900 psi, and allowing for a regulator failure that might spike the pressure to 3K and blow the disc....
That of course is entirely different than running the same tube, day in and day out, to 3000 psi.... Just because it will stand it once, doesn't mean the MSWP of the gun is 3000 psi.... It may indeed be safe for that.... but I'm guessing if you asked Umarex they would not tell you that was OK.... If you know the tube material and can do the safety calculations, then fine.... otherwise I would replace the tube with a known quantity that we know IS safe for a 3000 psi MSWP.... Alternately, you could test the assembled Gauntlet to at least 9000 psi to make sure there is a 3:1 safety margin....
Bob
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Maybe a disco tube is a alternative, those a good for 3000 psi with stronger valve screws.
I took a close look at a disembly vid of the umarex and it looks very conventional to a disco or a pr900w.
You could probably buy a disco tube to cut down and use the disco valve with the umarex hammer assembly and you drop-block.
Make only sure that you drop block is safe for 3000psi and is pinned with screws rated to that as well!
I did see that you have a corthan valve, are this a valve made for this gun or for the disco?
Or you could make a new airtube from crmoly, the dimensions Bob gave would be safe for 4500 psi fill (97200 psi Tensile Strength tube will give a 14000+psi burst)and with a stronger bottle you would have no problems reaching you goal of 110fpe with 25"barrel and 47gr slugs...
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110 fpe with bowmans, 25" barrel and balanced valve
at 3000 psi should be achievable as I got 100 fpe with traditional valve and 24" barrel.
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The manual stated do not exceed 2100psi. This could indicate they tested to 2100psi for the tube but I am not sure. The regulator is supposed to be set at 1900psi but I tested and found it at 1700psi. Since then I up the reg pressure to 2000psi. I may need to lower it down to 1900psi instead.
I have a disco tube but I have never seen or heard of anyone using the disco tube to 3000psi? Have you Jim? I may have to sort out proven material or use a parts gun that's rated to 3000psi.
The valve is made for disco so if I want to use 3000psi I need a longer 3000psi tube.
I think I am going to give the Bowman a hard look. But I am going to assemble the Cothtan valve and just see what it's doing At 2000psi and 25cc plenum while looking to replace/extend it.
RKR, that sounds a little more promising since you got some data I can relate to.
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The best I have done with my Hayabusa at 3000 psi with the Bowmans is 113 FPE (flat out maximum) with a 29" barrel.... The gun had porting larger than bore area, except that it did have a bolt probe in the chamber that reduced the equivalent area to that of a 0.206" diameter.... I sincerely doubt that just that single change to a retracting bolt face would make up for a 4" deficit in barrel length, but perhaps others can achieve better results than I can....
To achieve that 113 FPE the gun was using a LOT of air.... To get a realistic shot count, even with such a large reservoir, I had to back the power down to 98 FPE, at which point it was doing 1.20 FPE/CI.... This is typical of any unregulated PCP, what you can achieve for a maximum is significantly more than what you can tune it to shoot at, unless you are tethering the gun, and don't care how much air you use or how loud it is....
Knowing first hand what I got just a month ago with a balanced valve that was capable of handling a .357 cal.... is why I said I thought you would do well to achieve 950 fps with the 47 gr. Bowmans with a 25" barrel at 3000 psi.... YMMV of course, but you did ask for my advice.... There is no difference in the power that can be achieved with a balanced valve over a conventional one, you can just do it with less hammer strike.... If you are not planning on retracting the bolt face so that you can achieve full bore-area porting throughout, you will do well to even get to that FPE with a 25" barrel at 3000 psi with a usable tune, IMO....
Bob
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Yes I did ask for your advice and I got all the answers from you and everyone. This is my first slug build so I am ready to absorb any useful information from you gentlemen. Thank you all. I am all about performance and less asthetics. As long as it shoots accurately at 100-150yards, I can go with any weight as long as it works with 1-14 twist I have. Going to get a tube for 3000psi but will play with current setup for lighter slugs.
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Mr RKR,
Was your BSA regulated? If so what model of BSA and pressure?
I am ordering the Bowman now.
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Bob, I understood that a balanced valve will open and close more quickly thus allowing more flow at the beginning and end of the valve action? With my BSA I need to use super tight spring to get enough dwell, having the valve pop open more quickly should get the bullet moving a bit faster and thus get me some more fps?
Duy, I built the gun from old BSA Hornet. Took off the useless regulator and shoot it tethered. Got this shotstring with Bowmans, tune for max power and 3300 psi fill (BSAs are made for 3300psi fills). That's with a short 325mm airtube.
230 bar
941 fps
957 fps
970 fps = 100 fpe
960 fps
914 fps
158 bar
(https://farm5.staticflickr.com/4475/37178760223_0c8ca0e9ac_b.jpg)
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Open more quickly, maybe, if they are blowing open and you are not hitting them too hard.... but at maximum power the valve will still be driven open by the hammer and still be open when Elvis leaves the building.... which is why we don't tune that way, it just wastes air.... I have never found any increase in power with a balanced valve, and I have 3 different types now, in a total of 8 different guns, in 10 different calibers.... If you didn't have enough hammer strike to get maximum power with the conventional valve, then of course you get a increase with the balanced valve.... but the size of the porting and the pressure is the only thing that makes a difference in power, from my experience, in maximum power shots (ie what the plateau is)….
Does your BSA have a retracting bolt, or is there a probe remaining in the chamber on firing?....
Bob
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It makes sense since you had 8 balance valves that the main function of it's design is allowing light hammer strikes to open. The port size and dwell time when "Elvis" still in the house decides how fast he wants to get out. Am I correct?
I would love to see some of your own best designs for balanced valves I have read the "simplified balanced valves" but would like to see some actual pictures of the insides. Drawings are good but somehow actual parts made from drawings gives me courage to make one cause someone made one reasoning.
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My BSA has a needle nose probe, 1.5mm needle. I was planning to use pull back probe but it would have needed some major breech modifications.
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rkr, your results are almost identical to my Hayabusa at 3000 psi, adjusting for the difference in barrel length (25" vs 29" ) and probe diameter (0.216" vs 0.206" equivalent).... I got 113 FPE, and would predict 102 FPE for your gun with the Bowmans at 3000 psi for the plateau.... My recent .224 build, when corrected to the barrel length and pressure of your gun, actually falls slightly below your 100 FPE....
duy, larger ports allow shorter dwell to accelerate Elvis quicker.... but at the limit, with wide open porting, the type of valve seems to make no difference in the potential maximum FPE.... That is governed by barrel volume and pressure.... All that is happening in the first stage of the valve cycle is that the pressure behind the pellet is rising, there is no real airflow occurring, because the pellet has either not moved, or moved maybe 1/4".... Port diameter becomes important later in the valve cycle, when most of the airflow is occurring because the pellet is retreating down the barrel at high speed.... If the valve remains open until the pellet has left the muzzle, then dwell is meaningless, and so are opening and closing rates of the valve.... We are left only with port size (bore area being the maximum usable), pressure, caliber and barrel length as the factors governing FPE....
Bob
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if there is a way to know when exactly Elvis left the barrel and control valve closing time At the maximum port size, at that exact moment Then we have a winner...
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Sort of.... That would give you the maximum possible FPE without "wasting" any air (but you are using that air very inefficiently).... HOWEVER, if you close the valve when the pellet is only halfway to the muzzle, you have used only half that much air.... but the velocity will only be about 2-3% less.... Obviously getting 95% of the energy on half the air is MUCH more efficient....
1. If you keep the valve open until the reservoir is empty (long after Elvis departed), your efficiency approaches zero....
2. If you close that valve the instant Elvis goes out the door, it will be around 0.3-0.5 FPE/CI.... but the same power as #1....
3. If you close the valve when he is only halfway to the exit, the efficiency will be about 0.8-1.0 FPE/CI.... with about 98% of the velocity still there....
4. If you close the valve when Elvis has only managed to get 1/4 of the way to the door, the efficiency will be about 1.2-1.3 FPE/CI.... but he will still be going 95% of the velocity of #1 when he gets to the exit (because the expanding air is still pushing him for the remaining 3/4 of the barrel length)….
This is the reason we don't tune our guns "flat out" and operate them on the plateau (although a few big bores are incorrectly tuned that way)…. Just closing the valve at about the halfway point can double your shot count with hardly any velocity loss.... That is a very good way to tune a gun that you are going to tether, but you still want a couple of shots off tether.... If you want a bell curve with a reasonable shot count, you will be closing the valve MUCH earlier.... and sacrificing maximum power for shot count and efficiency.... This occurs at about 95% of the plateau velocity (roughly 90% of peak FPE)…. Therefore, if you figure your gun is good for 100 FPE maximum, you will end up tuning it for about 90 FPE.... Otherwise you will get a shot string where the velocity falls with every shot, and the gun will be an air hog....
Bob
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Thanks for your input. I haven't thought that far ahead other than fpe focused. Efficiency at 95% of maximum fpe sounds excellent. I thinK I will plateau it out and then tune it back for efficiency. I have a 2900psi parts gun on The way.
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I think I will plateau it out and then tune it back for efficiency.
EXACTLY the way to proceed.... Unregulated you will have to tune it back far enough to get a shallow bell curve anyways.... If you want to shoot at over 100 yards, you will want a narrow ES, which means you won't have to tune it back very far.... Good Luck....
Bob
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I think I will plateau it out and then tune it back for efficiency.
EXACTLY the way to proceed.... Unregulated you will have to tune it back far enough to get a shallow bell curve anyways.... If you want to shoot at over 100 yards, you will want a narrow ES, which means you won't have to tune it back very far.... Good Luck....
Bob
Thank you. I actually have a 2900psi tube coming in and will want to regulate to get the narrow ES. I think I am fine regulating it 2800-2900psi with a burst of 3k. I think I may have a limit of extending the plenum to 50cc max. I need to see the actual tube from a parts gun to figure that out. Still limited in plenum but much better than 25cc for sure.
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What are you going to feed the tube from, with an output pressure of 2900 psi?.... The bottle on the Gauntlet is only 3000 psi.... Are you getting a 4500 psi bottle?.... If not, you will only get a couple of shots before dropping below the setpoint....
Bob
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I have a 4500 psi bottle I can tether from And is ordering a smaller 4500psi bottle. Will need to make a custom dropblock unless someone can point me to dropblock rated for 3000/4500psi?
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Ask Travis at JSAR, they may have something.... I know of no other source.... The fastening to the tube is the issue, if you are running a 4500 psi bottle, they need to have a full 3:1 or more safety margin at 3000 psi, as do the valve screws, because a regulator failure will instantly reduce that to 2:1....
Bob
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What do you think about four 10-32 low head alloys that fits flush with the head bearing the pressure at 1/4's end of the tube? Should I go 1/2? The same type of alloy screws that is supplied with conthran valve kit. The valve will also be secured with 3 of the 10-32 low heads.
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That should be fine, providing they are not too close to the end of the tube.... You want the distance from the C/L of the hole to be at least 1.5 hole diameters from the end of the tube.... ie the remaining web between the hole and the end must be at least as large as the hole.... The holes and screws must, of course, be accurately located, so that the load is shared equally....
Bob
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just got me 2 molds for .225 39grains and .172 26 grains during the 10 year anniversay sale from NOE.
.172 barrel coming from LW Germany (might as well). and my 2900psi tube got here not too long ago from a Storm Rider. just waiting on carbon bottle and a drop block
the only hick up is that the Cothran valve is puffing air every shot by the securing 10-32 screws and back at the valve pin. looks like i need to seal it with an oring groove and thread tape. hmmm...
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so i have been playing with the how and why i should go with the gaunlet and working out the kinks with the cothran valve.
with the slightly longer than the stock tube shooting 33.95gr and my own custom 46 grains in .25 cal. these are the results
1300psi=855fps/34gr-55fpe
1300psi=756fps/46gr-58fpe
1700psi=880fps/34gr-58fpe
1700psi=788fps/46gr-63fpe
2000psi=924fps/34gr-64fpe
2000psi=835fps/46gr-71fpe
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modded gauntlet valve.
1300psi=800fps/34gr-48fpe
2000psi=909fps/34gr-62fpe
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.22 pellets
2800psi=1140fps/14.3gr
2800psi=980fps /28.6gr=61fpe
2800psi=835fps /42.9gr=67fpe
based on this i am going to go with the 2900psi tube cut to the QBs tube length.
the Cothran valve's long retaining screws has been shortened. the valve pin has a micro groove for oring later on, it has been wasting air and loosing pressure before hitting the pellet. also machined the valve retaining block on the gaunlet to fit the cothran valve and added a small push rod pin.
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Nice work . Out of curiosity do you know the mag length ? Looks like you’re well On your way .
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Nice work . Out of curiosity do you know the mag length ? Looks like you’re well On your way .
the max pellet the Gauntlet .25cal mag will take is .455. the 225 mold i ordered has slug length .410 and my custom pellet is .421.
the width of the .25 mag is .685
i updated the higher psi regulator testings...i am stoked. im going to swap the stock valve and compare. but that valve has bouncing problems, while the Cothran is minimal. i recorded the action with slow motion. i am not too worried about that right now.
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Wow , great work Duy !!!
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Wow , great work Duy !!!
thanks bother, looks like some parts are coming in. still lots of work to do to the breech and barrel before final assembly but things are moving along. really need to convert that 2900 psi tube before the carbon bottle arrives.
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Wow , great work Duy !!!
thanks bother, looks like some parts are coming in. still lots of work to do to the breech and barrel before final assembly but things are moving along. really need to convert that 2900 psi tube before the carbon bottle arrives.
Nice build, nice work.
Once you start getting into the higher FPE range the Gauntlet/QB repeaters have a weak link.... The breech flexes at the mag slot. Something to think about. I've thought of many ways to reinforce the breech, the easiest would be some type of solid scope mount that traverses the mag slot. it would have to be notched on the right side for the magazine to clear, if using mags.
I look forward to seeing this one progress.
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If the receiver is flexing, somebody should manufacture a figure-eight barrel band to fit over the shroud and main tube, immediately in front of the receiver.... to clamp the front of it down....
Bob
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I assume it flexes during the shot cycle via the transfer port?
if so, making a clamp and attaches the front of the breech to the main tube should work, so will Bobs suggestion. well, the barrel is kind of pointing up towards 12 oclock via the barrel band, i need to address it by clamping the receiver down...more work
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Bob, i am ready to sit and absorp some lessons about 1cc per fpe. is there a reason to why this is better against low cc vs high fpe?
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Bob's suggestion would definitely help with the flex. it occurs at the breech mounting screw, if you consider what is expected of that area, there isn't much metal to do the job....
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Duy, if the plenum volume is too small, the pressure drops during the shot.... This is because the response time of the regulator is much slower than the shot cycle.... The more FPE you ask the gun to produce, the more air it needs.... This drops the pressure more, and limits the FPE you can get.... A plenum of 1 cc per FPE is large enough to keep the pressure drop within reason.... You can get away with half that (1/2 cc per FPE), but you will have to compensate by increasing the setpoint pressure of the regulator about 10% to bring the average pressure during the shot back up.... If you try and use a plenum of less than 1/2 cc per FPE, the efficiency drops even more, you need an even higher setpoint, and raising the setpoint reduces the "headroom" (the amount of pressure the bottle can drop before reaching the setpoint)…. These three factors will combine to reduce shot count.... Eventually, if you keep making the plenum smaller, you won't even be able to reach the same FPE....
Bob
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thanks Bob that makes sense. the idea is to try keep higher pressure up until the valve shuts by supplying volume right?
i think there is also another way on how to achieve targeted fpe with minimum volume i think. i am sure you have seen 1/2 cc per fpe guns with relatively low set points. ie. the gauntlet with 25cc making 50fpe at 1300psi.
there is also another gun (nova liberty) that is making 45fpe with only 8.5cc at 2600psi in .22 cal. 2600psi is high but thats only 8.5cc.
so the old saying "just another way to skin a cat" or my own saying "many ways to cook an egg" applys here. dont get me wrong, i still think the 1cc/fpe has alot more potential then using just the minimum volume to get there. obviously i would like to go with the 1cc/fpe solution but i am going to settle for 0.5cc/fpe since the 2900psi tube has limited length.
i am sure i will reach 85fpe with 70cc volume at 2900psi, but my next question would be the loss of fpe due to the smaller bore of .225 vs .250.
what is the relative formular to this Bob?
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I have learned long ago that while there are, indeed, many solutions to a problem, but fighting physics is a sure way to find an inefficient solution.... My .25 cal BRod makes 58 FPE with 34 gr. pellets on 1400 psi, and can get 64 shots per fill on a 500 cc bottle.... At only 50 FPE the shot count would be much higher.... The point is that if you make a valve that breathes well, you can get a lot of FPE at relatively low pressure.... but you will burn a lot of air doing it, and using a small plenum will just make it harder to do.... However, if you are happy with your results, then that's great.... 8)
If the barrel length and pressure is the same, and the porting is full bore area, with no restrictions, then FPE tends to be proportional to bore area.... so a .22 cal will have about 80% of the FPE of a .25 cal.... If, however, the ports feeding the barrel remain the same, and they are restricted for both calibers, then the FPE may be proportional to bore instead of the area, so closer to 90%.... Most likely, the answer will be somewhere between those two values....
Bob
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i have much to learn...i used to think "just go as fast as you can" and forget anything else. but now i am thinking: "go fast but get there efficiently." i got to this state of mind after reading so much about tuning for efficiency. I just got to find the balance within my limitations...
now i need to make sure its making minimum 100fpe on 25cal before swaping in the .224 barrel...fun 8)
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Something else to keep in mind.... It is easier to achieve a certain FPE level with a heavy pellet going slower.... It will therefore also be more efficient to do that, than to achieve the same FPE with a pellet travelling in the 900s.... Conversely a light pellet, travelling well over 1000 fps, takes a lot more air to drive it for the FPE it achieves....
Trajectory, of course, mainly depends on velocity, so faster is better.... while the BC has some effect on that, more as the range increases....
Wind drift has a "sweet spot" at around 800-900 fps, at higher and lower speeds it increases, slowly at first, then more drastically as you drop below 600 fps or exceed 1000 fps.... This is one reason that faster is not necessarily better....
For the above reasons (internal and external efficiency) I never tune my pellet shooters for over about 960 fps.... nor bullet shooters for over about 1050 fps.... I have some guns tuned at around 700 fps, because they get a lot of shots on little air.... My Grouse gun is a good example.... I get 16 shots at 20 FPE (18.1 gr. @ 700 fps, unregulated), from a reservoir of only 65 cc filled to 2000 psi.... 8)
Bob
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My Grouse gun is a good example.... I get 16 shots at 20 FPE (18.1 gr. @ 700 fps, unregulated), from a reservoir of only 65 cc filled to 2000 psi.... 8)
Bob
you got to show that gun or link it Bob. thats awesome. taking notes...
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I built it before coming to the GTA, so there is no build thread here.... but this is a photo of it....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2260PCPCarbineEmail.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/2260PCPCarbineEmail.jpg.html)
It is based on a Crosman 2260 tube and a 14.5" barrel, trigger and stock from the 2289 pumper....
Bob
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Well...
I had a completely change of direction from Gauntlet to marauder platform.
the Gauntlet would probably be fine but the small plenum had me thinking hard, before i know it i had acquired a gen 1 marauder complete parts gun minus the stock for $100.
Baker big bore breech, RAI tube and drop block, RTI external adjustable regulator, 500cc Carbon bottle. Cothran valve.
almost Nothing on this build is "plug and Play"
Cothran valve had to be fitted with 1/2 od transfer body and 1/4 port. RAI tube had to be milled for Gen 1 marauder parts. Baker breech is Gen 1...and synthetic stock is gen 2 and needs to be fitted on. dont wanna go with wood since this assembly is already heavy...maybe 4-5 lbs already?
barrel is now 24.5 inches...i screwed up some...eh...i got a 30 cal 31 inch long coming from TJ... we will see how that goes fitted on this later on
i have a 22lr chamber reamer and that worked wonderfully. seating a slug is not butter smooth but very doable once sizing down from 225 to 224
anyway it took a while but here she is 85cc measured with fluid. i could use some more but its a better start. hopeful for a test soon.
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Awesome build , I’m really starting to like the .223/224 bullets . I’ll just received a pile of the RWS 41 grainers from Krale, super expensive but this is in the name of science . Hahahha
Post some groups ASAP .
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I think people will really start digging this caliber, as it has some definite advantages over .257.... There are two stumbling blocks for really high powered .224s, and that is barrel twist rate and bullet availability.... The 14" TJ's will handle the 47 gr. Bowman by Arsenal, which is a scaled down 257420, but anything heavier than that needs a faster twist....
(http://arsenalmolds.com/image/cache/catalog/224%20Bob%20Sterne-500x500.JPG)
http://arsenalmolds.com/products?product_id=165&limit=99999999999 (http://arsenalmolds.com/products?product_id=165&limit=99999999999)
TJ's does, however, have a 9" twist available (I have one), and I think a 12" as well.... There is not a lot of bullet choice, however.... the one I would really like to see has generated no interest at NOE....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/224%20cal%2065%20gr%20HP_zpscmnh5t46.png)
http://noebulletmolds.com/smf/index.php/topic,1135.0.html (http://noebulletmolds.com/smf/index.php/topic,1135.0.html)
I'm pretty sure that bullet would work OK in the 9" twist TJ's.... but unless others express an interest, I'll never find out.... ::) …. I'd even be happy with the 60 gr, about 58 gr. as a HP....
http://noebulletmolds.com/smf/index.php/topic,1134.0.html (http://noebulletmolds.com/smf/index.php/topic,1134.0.html)
Bob
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Denis id like to see some pictures of the 41 grains. will post some numbers before accuracy test next few weeks.
Bob you need to be a forerunner on some of these designs. if there is any accuracy data on these i would give it a try. i am too deep into this rabbit hole, cant get to the next one soon enough
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Here is what the 41.3 gr. RWS swaged bullets look like....
(https://i378.photobucket.com/albums/oo221/rsterne/224%20Long%20Range%20PCP/224cal41_5gr.jpg) (http://s378.photobucket.com/user/rsterne/media/224%20Long%20Range%20PCP/224cal41_5gr.jpg.html)
They are basically RWS .22LR match bullets, but a couple thou larger diameter.... They measure 0.224"....
Bob
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Here’s my personal favorite . Shooting these from a 15.5:1” twist seems just about perfect . Looking at those RWS bullets makes me think of the “Huben “ bullets from MP molds .
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Denis, you have a shot group for those 39 grains?
The RWS has a long gas check vs boattail with huben. huben goes for $350. and Nielson has 26 grain swaged slugs that works with 17.7 twist. noe has rws in cast form i think.
Bob is there a way to calculate barrel length and fpe in relation?
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Duy, you can get a rough idea of the maximum FPE you are ever likely to see, but in reality there are so many variables you are better off with a good guess based on similar builds.... My Hayabusa .224 with 29" barrel at 3000 psi is over 100 FPE, but backed off to get decent efficiency it is just under 100 FPE with the RWS bullets.... That still puts them at over 1000 fps.... It uses full bore-area porting, of course.... This was a group shot with a Drummen Sinner at 100 M with the RWS bullets in Holland.... It measures 17mm, shot outside....
(https://i378.photobucket.com/albums/oo221/rsterne/224%20Long%20Range%20PCP/17mm_at100M_DrummenSinner223.jpg) (http://s378.photobucket.com/user/rsterne/media/224%20Long%20Range%20PCP/17mm_at100M_DrummenSinner223.jpg.html)
FPE is roughly proportional to barrel length for a maximum power shot.... It is also roughly proportional to the pressure.... The heel of the RWS bullet is not really a gas check shank, it is where the .22LR bullet sits inside the case.... The RWS is apparently marginal in a 16" twist, the guys using them in Holland use .22 Hornet barrels with a 14-15" twist.... I'm not sure why that would be, as the standard twist for a .22LR barrel (with the same bullet) is a 16".... However, the Dutch maintain that the RWS bullet is more accurate in a 14 or 15" twist barrel than a 16".... I know that the Lyman 225107 (and the NOE 225-39 FN clone of it, above) are fine in a 16".... The Arsenal 47 gr. Bowman was designed for a 14" twist....
Bob
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Here’s a pic of some six shot groups of the 225-39FN GC . They were shot at 70 yards at close to 900 fps form an Evanix barrel . I should also mention I was using Knifemakers gadget .
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thanks for the picture Denis.i also have the 225-39 mold and i am looking forward to shooting it at 100 yards. i hope to get 1 inch groups. i also have Knifes recipe, wanna make it before going to the range
if it doesn't, i may have to get the 47 bowman. i got the 39 grains cause it can probably fit in a marauder magazine with minimal mod. we will see.
17mm looks good to me at 100y, Bob.
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I think i just built me an air hog...i was testing the 55 grains at 2900psi going 850fps. thats 88 fpe and should push the 39 grains in the 990-1000fps.
but i was only getting 5 shots from 4200psi to 2300psi...and the last 2 shots were declining...
since this is cothran valve and will consume more air with heavy slugs. i think going with 39, 47 grains may give more shots...i don't know. i was hopping 10 shots minimum for an accuracy test today but i dont know about going to the range with a hand pump hahaha.
i gotta find the cliff with a lighter spring with the valve. any suggestions are welcomed to tune for efficiency...
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That Cothran Valve will dump a whole lot of air with even slightly too much hammer . I would try some different spring rates and maybe even free flight . If you have a way to shorten the hammer throw , I’d use that too. That is some impressive power . Looks like you’re making some pretty good headway . I have just recently installed my first Marauder trigger on one of my builds . Quite possibly the best trigger I’ve used yet , minus the lawyer spring of course.
Which valve are you using , the full .250 or .180 ?
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Reduce the hammer strike until you find the cliff (the point where the valve nearly stops firing at all)…. Then increase the hammer strike until the velocity is JUST stable, with a low ES.... You will use the least possible air that way.... An SSG will help as well, but tuning just above the cliff is the main thing....
Bob
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Denis, the valves exhaust is .250. i plan to enlarge for 30 caliber when the TJ liner gets here. the barrel is currently .218x .245 oblong...i still have more room to work with.
Bob, i can tune above the cliff with the gauntlet but i will have to sort new springs and make an ssg for this one. right now its oem hammer and spring backed out to the max.
ahh...i just sat and thought about it. previously i filled the bottled to 4ksi but the output was at 2ksi. so when i up the reg to 2.9ksi. i think i lost overall pressure in the bottle. don't know how much exactly from 4ksi to top 85cc from 2ksi to 2.9ksi. but i will do a shot string again to see the shot counts. i thought it was weird...
yep just confirmed it was actually 3.5ksi to 2.3ksi for 5 shots.
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getting better but not by much. starting pressure 4000psi ending 150bar.
reg set at 2900psi shooting 39 grains.
8 shots...2-3 shots tight es. but declining afterwards.
the cliff was pushing these at 450fps. only a 1/4 turn and on is the valve.
i may have to set the reg lower...much lower than 2900psi. i should get more shots by working the reg around 2500-2600psi and port the barrel out for more fpe.
any other suggestions? i think my huben 22 has better shot counts haha
i recovered the 55 grains that was going 300fps. at that setting its very efficient haha.
this is clearly a deficit of the short 24 inch barrel and caliber size 224 vs 257 or 308
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There’s something definitely not adding up . With 500 cc you should be doing way better than that . It must be some loud with that much air getting passed through the barrel . I doubt you’ll gain very much by lowering the reg pressure to say 2600 psi ( just shy of 950fps ) . I’m getting close to the same power from a 480 cc bottle for 36 shots for example using a cobra chamber on my rifle . Is it possible that the valve is hanging up open due to the big ports . Maybe try a smaller transfer port close to full porting in 22 cal . There’s also a chance the valve has a bad shuttle and once open is dumping all the air in the plenum , only to close when the regulator moves enough air to seat the valve .
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It sounded like a rimfire and it rings in your ears but not as long and no sonic crack. I have no idea what the valve is doing atm. It maybe dumping all 85cc per shot, that explains why the first 3 shots already brought the 500cc bottle down to 200bar and it keeps declining from there. ill open it up again and see if it's internals are assembled correctly. I thought i did but it could be me. I can make a smaller TP and see if it's any better.
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Here are typical curves for a Cothran valve, plotting velocity vs. hammer strike....
(https://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg.html)
Note that the velocity is essentially constant, and as you reduce the hammer strike (in this case by increasing the SSG gap) the velocity suddenly drops drastically (which I call falling over the cliff)…. On the edge of the cliff, the velocity tends to become very unstable, and you can have shot-to-shot velocity swings of 50-200 fps, which is obviously useless.... At the bottom of the cliff, the gun barely "pops" (a 50% or more drop in velocity), or may nor fire at all.... and you get virtually no pressure drop on firing....
The best place to tune a Cothran valve is just above the cliff, but far enough up on the plateau that the velocity is stable.... In the above examples, that would be about 3 turns of gap on the black line, 5.5 turns of gap on the red line, and 6 turns of gap on the blue line.... Increasing the hammer strike (reducing the SSG gap) more than that will progressively use more and more air, and the effect can be very dramatic.... It is possible to reduce the volume of air used to 50% or more by tuning close to the cliff, rather than just bashing the valve open with brute force....
If you are tuning just above the cliff and the gun is using huge amounts of air (eg. dumping the 85 cc plenum), then you must have either a LOT of hammer bounce (reopening the valve after the bullet has left the muzzle), or something else going on.... Did you modify the Cothran valve in any way?.... eg. remove the metering rod from inside the valve stem, drill out anything, or change the way the balance piston is mounted in the front of the valve?.... The balance piston is supposed to be free-floating in the front housing, with virtually no axial (fore and aft) play, but able to move radially (sideways and up and down)…. That allows it to self-align with the moving poppet.... Maybe your poppet is sticking open until the plenum dumps for some reason?....
Bob
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i have not mod the valve in anyway. i opened it up once and assembled the metering rod with the machined smaller end towards the stem. which should be correct. ill make and ssg to eliminate bounce
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opened her up. nothing seemed out of the ordinary. lots of silicone oil i accidentally put in the valve and tube though. cleaned up and now shes shooting 10 shots from 4100psi to 180bars. reg still sits at 2800psi. got 39grains to top out at 1003fps. going to try again...10 shots is doable. want to see if i can get 15 or more.
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12 shots that averaged at 988fps. i wanna tune it down to 960fps for 80fpe.
the 55 grains were going 865fps...
no ssg yet. i probably need to go lighter on hammer weight.
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13 shots averaging about 990 fps with 39 gr. is 13 x 85= 1104 FPE total....
500 cc is 30.5 CI and the pressure drop is 110 bar, which is 3355 std. CI.... That works out to only (1104 / 3355) = 0.33 FPe/CI, which so me indicates that the valve is staying open until after the bullet has left the muzzle....
For some reason, your valve is remaining open MUCH too long.... Have you tried reducing the hammer strike until the velocity drops suddenly below 500 fps and then increasing it slightly from there until you are back close to 900?....
Bob
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yes i have tried from 300fps to 950fps by 1/2 turn. 1000fps is 1 turn from 300fps. right now i am trying to find the plateau then will tune down later. i think at 950fps which is just above the cliff will also yield but only a couple more shots...0.33 fpe sounds horrible. the regulator nno longer holds...the bleed hole keeps hissing air when i increase pressure from 0 bar to onwards. it was sitting at 4000psi and reg at 2900psi when it suddenly lets air out via the breathing hole...i think it is blown. so test on halt
any idea how and why the reg does that? it wont seal anymore when i increase pressure.
i am also thinking 77.6grams hammer weight is too much and it bounces?
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That hammer is some heavy for what you’re using . I’d be trying close to 40 grams . Can’t help with the regulator . Never had that happen . If your valve is working well and you’ve tuned it to just above the knee and stop dumping air , one I’d start looking for reduced hammer weight and second , a weaker spring . These valves open wayyyyyyyy easier than one would think .
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A half turn between 300 and 1000 sounds like you have a heavy hammer strike.... That could be hammer weight, but is more likely too strong a spring.... As Denis said, the Cothran valve is very easy to open.... An SSG should eliminate any hammer bounce problem, particularly if you are only 1/2 turn from the cliff..... Sounds like you have some other problem....
Bob
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i have a fixed 2800psi regulator i can still keep running tests. but the rti reg needs to be looked at.
ya, i am thinking about a slingshot hammer with less weight. that way i can keep the oem spring and oem tension adjuster.
who said building airguns was as easy as 1,2,3 right?
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I’m finding it strange that even with the regulator you have a declining shot string . I would think you would get at least 5 shots on regulation . Is it at all possible that your hammer is hanging up ? Either on the cocking pin or on the sear ?
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i have travel marks left by the hammer on the bottom inside the tube. if that tell you anything.
i noticed that too. but these slugs are not weighted and sorted so i thought it was variation of pushing heavier slugs or something like that. but it does look like a very fast declining string
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The velocity with a Cothran valve decreases with pressure.... If your regulator is typical, as the pressure in the tank decreases, the output pressure drops slightly.... This will cause a slight decline to the velocity, even if the regulator is working properly.... That 13 fps drop you are seeing in the first 10 shots could be due to that effect....
Bob
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that sounds like your describing what the reg was doing and its true. i keep watching the reg after every shot, and it seems to decline ever so slightly even when the bottle still has well over 200 bars. this reg was creeping at first but now the creeping is gone after only over 50 shots or so. such a nice reg. need to send it to RTI...but i wanna open it so bad...
ill make a slingshot with interchangable 25-35-45 grams and work on the efficiency this weekend.
TJ .308 31 inches long just came in...i think the cothran deserves .250 bore and up.
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I experienced my Cothran(s) staying open way too long (in spite of a light hammer and free flight) and wasting a ton of air---when using porting of .200 or smaller. I sleeved the stem to create a restriction and this resulted in the valve closing sooner. It has been debated why this occurred and I can't tell you the 100% accurate science behind it, but it did indeed work.
I would be interested to see if this worked for you as well. I used icemaker tubing as a temporary sleeve, it lasted long enough to test. now I have brass tubing epoxied in place. But, now that you have a 31" .308 barrel your .224 journey may hit a detour...
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Not a detour Mike. think of all the calibers as contenders for the platform. whatever gives the best power, efficiency, and accuracy gets to be mounted. but i am partial to the .224. the .30 or .172 is optional, they can always go to another marauder as i have purchased another breech and tube from crosman.
i can probably try your sleeving method, seems easy enough but with a disassembly. ill show and tell how the slingshot hammer works soon
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Dont mind me guys, i am just documenting my findings. and what do ya know? this thing shows promise.
i tried drilling the stem hole bigger, went with .04 but the cheap drill broke so filed it away and re-drilled to 1.5mm.
the 55 grains were going 860fps for 23 shots from 4000psi to 2600psi. thats way better than before for shot counts and at the same FPE. rough numbers from chinese regulator but its something
the 39 grains were going slower at 977fps compared to 1009fps. i didnt do a shot string on the 39 grains.
aired up and shot at 10 yards just to find out if its gun range ready.
3 shots(all i had) 55 grains sized .223, same hole
5 shots, 39 grains sized .224, 0.6 inches
5 shots, 39 grains sized .223, 0.54 inches.
well now, i still dont have an ssg. stock spring and maybe 10 grains lighter hammer since i reamed the ID from 0.500 to 0.530 for shorter spring but that spring was too short.
so i gotta cast some more 55 grains, 47 grains, and 39 grains to go to the range and find out what it does at 55 and 100 yards.
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That looks very much like the first test of my .224. I ended up adding a barrel band to make it accurate. With that thin barrel cf sleeve might also be a good idea.
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yah, iam gonna make a shroud and barrel band at the same time. i am stoked about the same hole 55 grains on the far left though.
i have yet to test the 47 grains. also ordered a tube to make it longer for more plenum.
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Another documentation. dont mind me guys
i have gotten the gun to shoot 55.6grains max at 881FPS for 96 FPE at 2800psi. i think can getting closer to 100FPE if i bump the regulator pressure to 3000psi or more. i will never build anything with shorter than 29" barrels anymore lol.
With 1.5mm stem vent hole. this thing is ultra adjustable! and with a shortened spring, i can tune on the cliff just as easily with the oem hammer. i can go from 750fps to 880fps with the 55 grains. and the 47 grains maxed out at 956fps. i am guessing i will get a couple of more shots from 23. I am liking it.
still havent been able to go to the range, but i am piling up 55 grains 47 grains and 39 grains. currently tuned at 89 fpe. i think thats good enough if the 55grains can touch something at 50yard and the 47 grains touching something at 100 yards.