GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Big Bore AirGun Gate => Topic started by: Fullblown on October 24, 2016, 10:05:35 PM
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https://m.youtube.com/watch?feature=youtu.be&v=5es7Ta4mh5g
Using .35 caliber 82 grain JSBs. 3 power shots over 200fpe or 10 shots at around 70fpe. Still working out the kinks though. Stay tuned
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Only part of a disco left was fill nipple LOL
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I would back up quite a ways from the chrony. hope your not reading the High Pressure Air flying over those screens.
Big bores have a problem with this phenomenom and require at least 6-10' of spacing from the chrono
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Certainly not impossible.... I have managed 192 FPE with my Disco Double in .357 with a 28" barrel on 3000 psi with ports that were 0.219", for one shot.... although it was with a 132 gr. bullet, not an 82 gr. pellet.... Impressive to say the least.... We need more details to properly evaluate this accomplishment....
Bob
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The build has a Disco tube, Cothran Powerhouse valve with .250 transfer hole, a 21 inch barrel and upgraded valve and breech screws. Got around 10 consistent shots at 70 fpe when filled to 3000psi. The power adjuster helped out with balancing that shot string. The first time it was shot, it was filled to 2500psi and went from 120fpe up to 240fpe.
The chrony is reading as it should. Just got to get this thing sorted out to about 5 good shots.
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I just want to make sure I got that right.... You got 240 FPE at 2500 psi with a 21" barrel and 1/4" ports?....
Bob
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Ooohhh.....
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Any pics of the rifle?
Joe
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733, 1048, 1153, 683
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I assume those are velocities.... without a fill pressure and an ending pressure, I still have no idea what is going on.... but I would sure like to....
Bob
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Those are velocities RSTRNE. No fill pressures because there is no gauge on the tube. Replaced it with a block. Will try to get a better video with a shot string on the gun. That was the first time the gun was shot. The goal is 150 fpe with pellets.
Hopefully someone will tell me what that acronym stands for.
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I just want to make sure I got that right.... You got 240 FPE at 2500 psi with a 21" barrel and 1/4" ports?....
Bob
Didnt happen with those specs. No chance no way. 120fpe yes but 240 is out of the question there simply isnt enough stored energy thats useful in that short of a barrel to hit 240 fpe at 2500psi.
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Looks interesting, but I would really like to see the numbers with the chrony further away from the muzzle.
Sound of the discharge bothers me somewhat or is it just the mic not picking it up. Or does it have ldc on it?
Do test more and more details please.
Marko
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Congratulations on the build brother! The cothran valve definitely puts out some power. Looks like from the video that you have a sleeved barrel? Also, what others have said, may want to back up about 6 feet or so. I see the grass being hit hard right behind your chrony. Honestly I've done the same thing, then moved it back on someone else's suggestion, and had my own... uh oh...moment :D. Please continue to post results, everyone is here to cheer you on and help!
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Andre - Are you working with Troy on this? I've been following his posts on the Facebook groups.
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DMEGUY, Yes I'm working with Troy. In fact, trying to get a good video in right now before it gets too dark. I actually spoke to a few shops today about some new parts for a 45 build since this build looks extremely promising.
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Well you guys were right! A little too close to the chrony. Got 5 shots ranging from 715 down to 685. Shucks!! Back to the drawing board.
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Well you guys were right! A little too close to the chrony. Got 5 shots ranging from 715 down to 685. Shucks!! Back to the drawing board.
Thats what I come up with using my spread sheet. Up the barrel length and those numbers will climb a lot partner.
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Glad to see you got it sorted out.... For a while I was thinking the spreadsheet I have been using to calculate ballpark numbers was in the wrong ballpark.... Actually, those numbers seem pretty low.... The real potential probably lies between the two extremes.... My .357 Disco Double can do three shot strings at 170 FPE, starting from 3000 psi, ending at 2100, with 127 gr. bullets in a 24" barrel, and 0.219" ports.... You should be able to get about the same FPE with a 21" barrel with your larger ports.... but I still have 250 cc of reservoir available with the double tube setup, instead of only 135 cc.... With pellets I can get 10 shots at 125 FPE, so half that many with a single tube Disco should be attainable....
Bob
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Rsterne,
What valve are you using in your double to get those numbers?
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A Disco valve that I modded myself.... It has a 0.266" throat with a PEEK poppet and the stem is 1/8".... The exhaust port is 0.219" on a 20 deg. angle, and the transfer and barrel ports are also 7/32".... The valve was optimized for a .25 cal bullet shooter or a .30 cal pellet shooter, so is a bit undersized for a .357, even with pellets.... However, trying to get much more power from a Disco than what I did (my gun peaked at 192 FPE at 3000 psi) will leave you with just one shot per fill from the single 135 cc tube, without a drop in velocity.... I plan to install a Cothran Powerhouse Valve in my Disco Double as soon as I can get some shop time.... It is, in fact, my first winter project.... I am hoping for two shots of equal velocity as close to 200 FPE as I can get (with a 127 gr. bullet).... but I hate making predictions, there are just too many variables....
Bob
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The goal was to get a 5 shot string averaging 100fpe so you are giving me hope. I'm going to redo the transfer port and add a heavier spring tomorrow. We'll see what happens. A tip on the cothran valve. Use a front screw breech. The valve body has enough meat to drill and tap for a 6-32 bolt. I bought 5 of them at the depot for only .98¢ In stainless. I shortened one. Turned the head down on the lathe so it is the same dia. as the stock breech screw and you can attach the breech directly to the valve. Just drill the threads out of the tube. Very secure with the amount of air it pushes. It stripped the threads and blew the breech off during the first test. Wasn't using any barrel bands.
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My breech on the Disco Double currently uses a 4-40 SHCS tapped into the tube in between the front and back stock holes, but the breech has a breech band that holds down the front, so strength is not an issue....
Bob
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Got 3 shots today at 108fpe avg. Installed a heavier spring and a new brass transfer port. The rubber one I was using collapses in on its self when the breech was tightened and limited air flow. Getting a little blow by but once the new breech is made I should be able to fix that. Going to have a 150cc tube made for the gun and should get 5 shots over 100fpe. May look in to a longer barrel as an option. I just want to be able to offer the Airgun world over 100fpe Bigbore entry level gun @ $400 add your own trigger/stock. That's the reason I am going with the discovery/22xx trigger pattern. People can use the trigger group and stock off a 2260/ disco/ maximus/ 2289 that they already own or I can add a trigger group and stock and sell the full rifle. Accuracy tests begin tomorrow. Hopefully all goes as planned.
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Got 3 shots today at 108fpe avg. Installed a heavier spring and a new brass transfer port. The rubber one I was using collapses in on its self when the breech was tightened and limited air flow. Getting a little blow by but once the new breech is made I should be able to fix that. Going to have a 150cc tube made for the gun and should get 5 shots over 100fpe. May look in to a longer barrel as an option. I just want to be able to offer the Airgun world over 100fpe Bigbore entry level gun @ $400 add your own trigger/stock. That's the reason I am going with the discovery/22xx trigger pattern. People can use the trigger group and stock off a 2260/ disco/ maximus/ 2289 that they already own or I can add a trigger group and stock and sell the full rifle. Accuracy tests begin tomorrow. Hopefully all goes as planned.
Troy I can't tell you how bad and idea this is for you. The liability alone is enough to kill this idea but you will find like many before you that it costs far more than you think it will and profit margins will be very small. I'd suggest to you to make your own gun and share your results and have fun with it.JMHO
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I finally got to do some testing. 3300psi fill 5 shots starting at 823-730fps 108fpe avg ending at 1800 psi. Tube does still have a gauge block so that is taking up some room. Re-crowned the barrel and getting 5 shots a 50 yards less than 1-1/2" with the first 4 shots less than 3/4" at 50 yards. Using a Maximus stock and trigger. A better trigger will really help out as well.
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:D
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Sound like you can back down the hammer strike a bit and even out the shot string.... lose a bit on the first shot but use less air and end up with a narrower ES.... 11% is a bit of a spread, IMO....
Bob
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Rsterne I agree. It still needs some final tuning but darn happy with the grouping. Now to get started on the new breech.
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Rsterne I was able to acquire 24" barrels from the same maker. With new tubes made out of stainless 3500psi rated with out the gauge block and keeping .25" transfer port I believe 150+ fpe with pellets over 5 shots will be obtainable. Does that seem like asking too much?
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Just make sure that EVERY part of the gun is safe for 3500 psi.... Valve screws are an obvious one, but it's easy to forget things like the bolt handle shearing off when you fire the gun.... There is 350 lbs. of force on that ever time you pull the trigger, so at the ASME's 3.5:1 safety margin it needs to be good for 1225 lbs. without shearing off.... That's just an example of something you may not think of that could bite you....
5 shots at 150 FPE with pellets?.... You are still only dealing with 9 CI of volume without the gauge block.... However, if the stars align for you, you never know unless you try it.... I got 9 shots averaging 130 FPE with 77.5 gr. pellets with my Disco Double, starting from 3000 psi.... It had a 28" barrel and 0.220" ports, but it had over 15 CI of air in the reservoir....
Bob
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125fpe with pellets was what I meant and hoping 150fpe with some slugs. With the new longer barrels I may try to add an inch or two to the tube as well.
Thanks
Troy
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Annihilator .357 update:
Replaced the 21" .357 barrel, which was getting 108fpe, with a 28" barrel. Should put this rifle just beyond 135fpe. Chrony tests in the morning. Still have to fit the barrel band.
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Very nice, Troy.
Joe
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Very nice, Troy.
Joe
Thank you Joe. Still have to blue the barrel and dye the barrel band but it should look pretty good when I'm done.
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Need to put my .357 barrel to use.
Joe
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Annihilator .357 update
New 28" barrel. 1st shot 889.5 fps and 142fpe 3000 psi. Drops to 125fpe over 3 shots. Testing has shown this valve to work best on a regulator. Looks like a bottle fed baby to be born soon.
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Very cool!! Nice looking gun, your ready to hunt!!
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I really want to see it as a bottle fed beast and the numbers you get then. What regulator are you using?
Joe
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I really like the Robert Lane regulator. Will probably regulate the tube to 2000psi and run a 3000 psi tank.
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If you are using a separate bottle, I would think it would make the most sense to use a regulator that simply threads into the bottle, like a Ninja.... You can purchase them in any pressure you want, up to 3000 psi, in 200 psi increment (1800, 2000, 2200 etc.).... Since you are using a Disco as your base, and you want a gun that shoots over 135 FPE, using the full Disco tube as your plenum makes sense, as it is 135 cc.... The very simplest way to do this it to simply tether the bottle to the fill fitting on the front of the main tube....
I would not recommend using an in-tube regulator when going for over 100 FPE, you simply won't get enough plenum, unless you mount it in the front of the tube.... and then you will have to anchor it against the end force created by the pressure differential across it....
Bob
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That make sense Rsterne. Thank you again for the knowledge. Weren't you able to get over 125fpe @ only 1500psi or so? I'll have to go back and check your double disco cothran valve thread.
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With the 78 gr. JSB pellets I got 111-113 FPE at 1500 psi.... I got 131 @ 1900 psi and 137 FPE @ 2000 psi.... That was with a 28" barrel....
Bob
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This might be the perfect setup for a regulated double setup.
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Just a quick off the cuff calculation would go like this.... If we assume 2000 psi and 135 FPE, with an efficiency of 1.35 FPE/CI, that needs 100 std. CI of air per shot.... The lower tube is 120 cc (7.3 CI) at 3000 psi, and the setpoint is 2000 psi, so we have 1000 psi (69 bar) of "headroom" which gives us 7.3 x 69 = 504 std. CI of air available.... That should give you about 5 shots before the lower reservoir pressure drops below 2000 psi.... If you tether the gun to a 3000 psi regulator you can shoot as long as your SCBA tank lasts, and untether whenever you want for 5 shots.... Sound very workable to me....
Bob