GTA
All Springer/NP/PCP Air Gun Discussion General => American/U.S. Air Gun Gates => Crosman-Benjamin Air Gun Gate => Topic started by: Ryden on February 28, 2023, 05:05:49 AM
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I've got myself a Crosman Drifter and gone down the rabbit hole of modifications, for legal reasons I'm more or less stuck with the original barrel length of 14,6" so how much power can I really expect to get?
Will a bigger valve assembly be wasted?
The plastic pump doesn't feel reliable, but will a a metal pump for higher pressure make any difference with the short barrel?
A new trigger is a given, it's horrible!
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I've put a steel breech on it, and it's really amazingly accurate.
Even with a sloppy folding stock and a cheep scope, it will consistently make a ragged hole at 10m. Impressive.
A better scope is on its way, but is there no input about what tuning steps are worthwhile?
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I have built a 1322 with a 14.5" barrel. Testing for power now.
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Currently using layers of cardboard to test. Waiting on a chronograph.
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folded
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Very much like mine, those three shots are the first after tearing it down and rebuilding it completely, including fiddling with the sight
Quite astounding at 10m
(https://i.postimg.cc/JnSn5LHP/20230219-105737.jpg)
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13xx tunes, opening up the barrel port, valve porting, , and either filling some of the piston to get more power with less pumps, to a point. Or removing a couple threads on the valve and also removing some internal material from the valve, so it holds more pumps for more power with more pumps. With those mods, one may want to beef up the pump linkage pivots.
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Since the original poster and I are going down the same path, I will hijack if he doesn't mind. I drilled and bushed the big pivot and sized it for an aircraft grade bolt. I also lapped in some very thin washers to give a good lateral bearing surface. This is my 10.5" version. I plan to do the same to my carbine. 14.5" barrel. I also made a tighter fitting pin for the piston. Any way to beef up the riveted joint?
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I am trying the metal piston from Magnum Airpower along with his valve, but I won't have numbers until I get a chronograph and figuire out how measure valve volume and get some baseline numbers. link to that thread https://www.gatewaytoairguns.org/GTA/index.php?topic=206558.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=206558.0)
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Since the original poster and I are going down the same path, I will hijack if he doesn't mind.
By all means, feel free to add as much contributions as you like.
The more info we can get on one page the better
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13xx tunes, opening up the barrel port, valve porting, , and either filling some of the piston to get more power with less pumps, to a point. Or removing a couple threads on the valve and also removing some internal material from the valve, so it holds more pumps for more power with more pumps. With those mods, one may want to beef up the pump linkage pivots.
I get what your're saying about the ports and valve but im confused about filling the piston, could you please clarify?
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13xx tunes, opening up the barrel port, valve porting, , and either filling some of the piston to get more power with less pumps, to a point. Or removing a couple threads on the valve and also removing some internal material from the valve, so it holds more pumps for more power with more pumps. With those mods, one may want to beef up the pump linkage pivots.
I get what your're saying about the ports and valve but im confused about filling the piston, could you please clarify?
It would help if I used the right word, I meant valve, some use a larger plastic intake valve seal, or add some material inside the valve to take up space, so less air can be held, but holds it at higher pressure.
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Ok, I get you.
Less air, but more highly compressed.
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On my 14.5" barreled 1322, I bushed the front pivot, and installed the Magnum Airpower CUP-SEAL VALVE & PISTON KIT and apx. .148" transfer port and tested in my cardboard layer box. It exceeded the stock set-up at 10 pumps and beyond. Stock=20 layers at 10 pumps Modified=26 layers at 10 pumps Stock=26 layers at 15 pumps Modified=30 layers at 15 pumps Modified=38 layers at 20 pumps. I used a low sample number because I am receiving a chronograph soon(maybe tomorrow) and will do more testing with that as I can also do accuracy testing simultaniously. For reference, my Weihrauch HW 95 does 38 layers. It was tested new with 15.9 grain pellets for an average of 571 FPS or 11.51 FPE. I really feel that the rifle has broken-in and may be shooting faster.
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Front of my target box.
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I received my chronograph and tested the 1322, 14.5" barrel with Magnum Airpower valve and piston kit and oversized transfer port. 14.3 grain Crosman Premier Domed pellets.
10 pumps = average of 523.4 FPS and 8.7FPE. 15 pumps = average of 595.7 FPS and 11.27 FPE. 17 pumps = average 610.5 FPS and 11.84 FPE. 20 pumps = average 634.16 FPS and 12.77 FPE. The little Chinese chronograph is the bees knees for $30.00. Over 20 pumps was very erratic losing over 100 FPS at times. For reference my Weihrauch HW 95 with 12" barrel clocked at average of 669.6FPS and 14.24 FPE.
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For lower valve volume like James is talking about, some make their own fillers. Tack Driver 10 pointed me in this direction...
https://www.ebay.com/itm/112297985209 (https://www.ebay.com/itm/112297985209)
It is the check old style check valve from a 760. It is longer than the 13xx check valve and works very nicely. Drop out the original, drop this one in and done. ;)
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Thank you for the information, that check valve seems promising
I can't find it for sale in Europe though
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The 1377/1322 in stock form can hit 25 yards all day in the black. 10 meters is nothing these for these guns.
Put a x9 Power scope and 2 stage trigger on it and watch that grouping tighten up even more.
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Yes, I know. I've tried it out too 35 m
I was just surprised that a rifle that had been totally disassembled, modified and generally messed about could hit so extremely close to the aiming point with the first shot, especially since the front sight has been replaced and the rear sight has been changed