GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on February 07, 2015, 10:54:30 PM
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After months of planning and collecting parts while the Motel was too busy for me to get into the shop, I have finally made some progress on my latest project, converting an XS-60c (FD-PCP) to a .30 cal, regulated repeater.... The work starts at this point in this thread in the Chinese Gate.... http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.780 (http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.780)
The basis of the build is an XS-60c from stalwart with the receiver bored through to accept a 7/8"OD x 0.065" steel tube capable of handling 3000 psi.... It is no longer threaded into the receiver, and the valve and tank block will be mounted directly into the tube to allow 3000 psi with a 3:1 safety margin.... The valve is modded, the hammer, spring, and rear preload adjuster are new, the bolt is new, and the receiver is machined out to accept a seven shot .30 cal MRod magazine from Lloyd at AirGunLabs.... The gun will be powered by a 22 CI, 3000 psi tank equipped with a Ninja 2000 psi output regulator, both from Tim @ Mac1.... mounted in a custom reversed tank block I am making.... The 25" barrel is a TJ's with a 1/2" OD, designed by Sean Pero and I, with a .294 land and .300 groove and a 26" twist.... It is the same barrel that Tim used to win the Extreme Bench Rest recently.... Mine will be sleeved with a 0.595" OD carbon fibre sleeve and the receiver will be drilled to accept that slightly larger diameter.... and I plan to fit Hatsan Air Stripper to the muzzle....
Performance, ultimately, ends up being whatever you get, and I am using the same port sizes as in my Disco Double .30 cal, but that was a 3000 psi gun, and this one runs at 2000 psi.... I would be pretty happy to get two magazines in the 90 FPE range from this build, but only time will tell.... If you are interested, please follow the build in the thread linked above....
Bob
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Initial tests.... 87-100 FPE at 1800 psi.... and 115-138 FPE at 2900 psi.... These are tethered at those pressures, and the maximum achieved, dependant on pellet weight....
http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.880 (http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.880)
Bob
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Strings at 2200 psi regulated have been posted.... 92 FPE for 17 shots with 45 gr., 94 FPE for 18 shots with 50 gr., and 110 FPE for 14 shots for 70 gr.... Maximum power at 2200 psi is 102 FPE, 107 FPE, and 121 FPE, respectively.... Tank is 22CI / 3000 psi.... The Grizzly is a 7-shot .30 cal. repeater, and weighs just 6 lb. 14 oz. complete....
Bob
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I finally got a chance to let the Grizzly stretch it's legs today.... It was one ragged hole to groups you could cover with a quarter at 50 yards with both types of pellets tried, and at 100 yards there was a noticeable difference between the Daystate 50 gr. and FX 45 gr. pellets, with the FX performing slightly better.... Here is a 5 shot group from the bench at 100 yards, 970 fps.... Small squares are 1/2", large black squares are 2"....
(http://i378.photobucket.com/albums/oo221/rsterne/Flying%20Dragon%20PCP/Grizzly%20FX%20100%20yd001_zpsstcgntfc.jpg) (http://s378.photobucket.com/user/rsterne/media/Flying%20Dragon%20PCP/Grizzly%20FX%20100%20yd001_zpsstcgntfc.jpg.html)
I measures 1.30" C-T-C, so I'm very pleased.... It has the same trajectory, and the same scope (Hawke 3-12 x 44 SF) as my 2260 and 2560 HPA Varmint rifles, and is sighted in the same, all three being zeroed at 35 yards.... The POI is about 1 MilDot low at 50 yards, 2.5 Dots low at 75 yards, and the aim point is the top of the post (5 Dots low) at 100 yards on all three rifles, at 12X.... so I will be able to switch between rifles depending on the size of the quarry.... I'm really looking forward to introducing the Grizzly to Mr. Marmot in the near future....
Bob
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That is simply fantastic. I especially appreciate both the power and efficiency that you obtain from the 3000 and sub 3000psi levels. If I remember from reading, this barrel is a 20 or 24 twist? Youve tested the BBT for power, which I believe you designed specifically for these .30 barrels, how are they for accuracy? If I recall, I thought they perform better with a faster twist, but excited to see them in use. I have not found them anywhere, other than the mold availability.
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The barrel is a 26" twist, and I did not get a chance to test the BBT's for accuracy yet.... They should be fine in that twist rate, they were designed for it.... I don't know of anyone casting them for sale, but the molds are available from Accurate....
Bob
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Thanks Bob, glad to hear that. I did see the mold at Accurate and would have given it a shot if I was set up to cast, but might even get it to have someone cast for me.
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.30 cal Grizzly Meets Mr. Marmot....
http://www.gatewaytoairguns.org/GTA/index.php?topic=89969.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=89969.0)
Bob
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Hey Bob,
Love how when I am thinking about building a big bore (or anything) all I have to do is come to the GTA and look up your work to try and get ideas.
I'm planning on using an old discovery for the base of the build.
I have a source for barrel liners, I'm planning on purchasing a 28" 357/9mm liner from a gentleman.
Would you recommend 1cc/1fpe of plechamber regardless of barrel volume? I'm planning on using a regulated .6l CF cylinder with the reg pressure to be determined while testing the setup.
Thanks in advanced!
Cameron
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If you use 1 cc of plenum per FPE you want, you really can't go wrong.... If the gun is really efficient, you can go smaller.... If you are going for very low power for the caliber (which is generally very efficient) you can go smaller.... If you are installing an in-tube regulator, where increasing the plenum volume makes the main reservoir smaller, you are actually better to go smaller (as small as 1/2 cc per FPE) and increase the regulator setpoint to make up for it.... because at 1 cc per FPE your reservoir will be so small you will lose too many shots....
Since you are using a separate 0.61 L CF tank, your reservoir will be that size regardless of how big you make your plenum.... so I would make it as large as is reasonable.... Are you planning on shooting pellets (JSBs are about 81 gr.).... or bullets?.... If bullets, how much power are you after?.... You don't say if your CF tank is 3000 psi or 4500 psi.... If it's a 3000 psi fill, and you are regulating at about 2000 psi, you are very unlikely to be building a practical bullet shooter, IMO.... Even with a 28" barrel, 2000 psi would be hard pressed to get enough power to make a strong bullet shooter.... With 7mm (9/32") ports, which is not unusual for a .357/9mm.... you will be very lucky to hit 160 FPE (950 fps) with the 81 gr. JSBs with a 28" barrel at 2000 psi.... You should design for about a 150 cc minimum plenum to achieve that power....
Bob
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If you use 1 cc of plenum per FPE you want, you really can't go wrong.... If the gun is really efficient, you can go smaller.... If you are going for very low power for the caliber (which is generally very efficient) you can go smaller.... If you are installing an in-tube regulator, where increasing the plenum volume makes the main reservoir smaller, you are actually better to go smaller (as small as 1/2 cc per FPE) and increase the regulator setpoint to make up for it.... because at 1 cc per FPE your reservoir will be so small you will lose too many shots....
Since you are using a separate 0.61 L CF tank, your reservoir will be that size regardless of how big you make your plenum.... so I would make it as large as is reasonable.... Are you planning on shooting pellets (JSBs are about 81 gr.).... or bullets?.... If bullets, how much power are you after?.... You don't say if your CF tank is 3000 psi or 4500 psi.... If it's a 3000 psi fill, and you are regulating at about 2000 psi, you are very unlikely to be building a practical bullet shooter, IMO.... Even with a 28" barrel, 2000 psi would be hard pressed to get enough power to make a strong bullet shooter.... With 7mm (9/32") ports, which is not unusual for a .357/9mm.... you will be very lucky to hit 160 FPE (950 fps) with the 81 gr. JSBs with a 28" barrel at 2000 psi.... You should design for about a 150 cc minimum plenum to achieve that power....
Bob
Thanks for the response!
I'm not planning on shooting bullets, more than happy with the jsbs or anything that shoots well. I'll let the barrel choose what it wants to shoot.
I'm using a discovery tube, either a modified disco valve or homemade with a 23cuin 3000 psi bottle regged for testing, if I need the additional air volume I'll use a 4500psi .6l CF bottle.
I'm planning on finding the knee of my power curve and then slowly take up space in the air tube to find the minumum amount of CC's needed to maintain that level of power and then chop the air tube and install the bottle using a tank block.
160-200 fpe would be nice but I'd be happy with 150fpe, this will be a coyote gun and potential small pig gun. This is more just a fun experiment to see what I can put together.
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Running a Disco tube, I would run the whole tube as your plenum, that is 135 cc.... about right for a pellet shooter in .357 cal.... You may be able to shorten the tube, but if you do, you will have to increase the regulator setpoint to make up for the pressure drop during the shot from the smaller volume.... Eventually, FPE and efficiency will suffer if you try and use too small a plenum....
I would start by tethering the Disco tube, full size, to a regulated tank, until you know what you've got....
Bob