GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: dmrey on October 27, 2021, 10:03:54 PM
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New owner. Love the fact that the 1377 is a great platform to build upon. Even as a pistol, it's fun to shoot for accuracy indoors. I'm keeping it down to 2 pumps and get excellent performance from 10 ft with the pistol stabilized. I'll probably keep this one near stock, but am thinking about another one and want to go crazy with it (stock, long barrel, sites, advanced trigger/sear).
BUT - if I add a barrel, how much faster is it going to shoot? I'd prefer to keep it under 400 fps. I'm not shooting to kill anything except bullseyes.
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why would you add a longer barrel if you prefer it to shoot under 400 fps ?? to pump less I assume..??
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With the usual power mods, a longer barrel will add approximately 10 fps per inch.
For in depth knowledge on modding the 1377 and 2240 platforms, check out CAPOF.
https://www.crosman-air-pistol-owners-forum.com/board/index.php (https://www.crosman-air-pistol-owners-forum.com/board/index.php)
Not as active as GTA, but some great collected info there.
JMJinNC
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I'm no pro or guru when it comes to the 13XX platform, but was able to find a ton of various information while searching for my 1377.
A longer barrel will increase velocity, but I think you'll need more than 2 or 3 pumps to see any real gains.
For low pump/higher velocity look up "valve stuffing", I believe this will get you the most low pump gains. Basically, the idea is to minimise valve volume to achieve higher pressure (higher pressure/low volume will "slap" the pellet harder to get it moving). Use of a "plug" inside the valve spring and wire/rod was used, but if your handy with JB weld, I'm willing to bet you can take it even further.
Hope this helps a bit, wish you the best.
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Just an FYI, I made a 3-4 pump 1377-based target rifle for my kids. Muzzle velocities in the 465-525fps range shooting 7grain wadcutters.
19” barrel, stuffed valve, longer compression tube, flat top piston is what I needed to get it there.
Just so you know what’s needed to get there with low # of pumps.
JMJinNC
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why would you add a longer barrel if you prefer it to shoot under 400 fps ?? to pump less I assume..??
I assume a rifle is more accurate. Plus to scratch that 'mod/upgrade 1377 itch'.
I'm looking to build a poor man's target/match rifle - but I'm really on the "still new to this" side of the learning curve.
In other words - instead of spending $500 on a PCP intermediate grade rifle... I'd rather piece together a frankenpump (and find out it's still poop) for half the price. Half the fun will be the tinkering. The other half will be plinking from 5-10m.
If it wasn't for youtube - I never would have considered modifying a 1377 into something like a carbine/rifle.
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flat top hybrid 760/1377 low volume valve. pin in check valve, adjustable brass piston, 14.5" LW barrel...
7.4gr Crosman super points
508FPS @ 5 pumps
660 @ 10
732 @ 15
772 @ 20
the hybrid valve and brass piston were made by "tach driver 10" and this 1377 rocks!
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A longer barrel will increase velocity, but I think you'll need more than 2 or 3 pumps to see any real gains.
Hadn't considered that - increased pressure/volume release from the valve is required to get it thru the longer volume of the rifle.
I'm ok using the pistol 1377 at 2 pumps indoors.
As for an upgraded rifle version - I'm more interested in upgrading for upgrade sake ... not so much for keeping the pumps down to maintain the same velocity as the pistol. Shooting indoors - I will understand if it becomes necessary to upgrade my backstop from four pizza boxes ;)
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Gains with increase of barrel length will be greater when you pump more.... In fact at 1 or 2 pumps, you might even lose velocity.... At full pressure/pumps, gains in FPE are typically about proportional to barrel length.... ie a 20% increase in length will give about that increase in FPE, which means about 10% more velocity.... That is why "X fps per inch" is really not correct, as going from a 10" barrel to a 14" will give much greater gains than going from a 20" to a 24" (still 4", but half the percentage increase)....
Bob
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rsterne is a guru when it comes to barrels, valves, pressure and port sizes. Scrolling through the archives I've read a lot of his posts in regards to this stuff. I'm only just learning and at the beginning of this journey ;D
When it comes to upgrades, the sky is the limit it seems. There are plenty of vendors who offer stuff. At this time, the only one I can remember is Magnum Air Power, but have visited others. Then there's a ton of stuff on ebay and such for other upgrades, if you don't want to modify OEM parts yourself. I've been eyeing a brass pump piston, but not sure if I'm going that way or not.
Hadn't considered that - increased pressure/volume release from the valve is required to get it thru the longer volume of the rifle.
I'm ok using the pistol 1377 at 2 pumps indoors.
As for an upgraded rifle version - I'm more interested in upgrading for upgrade sake ... not so much for keeping the pumps down to maintain the same velocity as the pistol. Shooting indoors - I will understand if it becomes necessary to upgrade my backstop from four pizza boxes ;)
A long barrel,steel breech, modified valve and piston, shoulder stock, LDC/moderator... Sounds like what I want to do with my 1322 :D
Have fun and take care
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my 1377 has an 18" barrel, steel breech, enlarged transfer port & extended bolt probe. It is my favorite @ 20 yards. it is scoped