I’ve taken a major break from spring piston air rifles and have really been focusing on multistroke pneumatics lately. The Crosman 1377/22 is a very popular air pistol to modify, and I’ve tinkered with them off and on for the past 15 years. Here’s what I’m currently working with:
It currently has a 14.6″ barrel and will put out 540 fps with 14.3 grain pellets with the stock valve. I 3d printed a barrel band that keeps the barrel locked in place, enabling me to use the infamous Crosman intermounts with great results. It is topped with a LDC to quiet things down and is a fairly accurate shooter at 30 yards:
Today, I got a wild hair and decided I wanted to quiet it down further by conserving air in the valve. These normally dump all the air in the valve, which is noisy and inefficient. To retain air, I cut down a spring that was slightly heavier than the stock hammer spring. It is cut short enough to where there is no preload when it is reinstalled. Now it no longer dumps all the air, and functions loosely like a PCP. It lost a foot pound of energy, but is much quieter and smoother shooting than before. Here’s a chart showing the speed vs number of pumps from an empty valve:
There are a couple of ways to approach a setup like this. The first is to find a point where you can get 2 shots close in velocity without needing pumps in between. The magic number here was 23 pumps. This gave a first shot of 479.7 fps and a second shot of 483.9 fps. This gives 2 shots averaging 7.4 FPE, more than enough for close range small game hunting. A quick, no pump followup shot can be useful in many situations.
The second approach is to figure out how many followup pumps can be used after pumping to the maximum velocity to give a consistent shot string with a minimal recharge pumps. I determined that 9 pumps between shots would give me an average of 501 fps with an extreme spread of 12.7. Ultimately, this saves me a pump each shot with much less noise and vibration than before. This easy modification has been well worth the little effort.
The 13XX platform really needs an oil wiper to produce consistent speed. I guess a better piston with a wiper will have to be my next project. This should push me over the 8 FPE mark and tighten up that extreme spread even further.