I’ve finally gotten in the parts I was needing to continue working on my 1322 ACP (air conserving pumper). One of those parts was a flat top valve and piston set from Airgunsmith. I highly recommend this setup, as the parts are well machined and thought out. The primary reason I chose this setup was for the felt oiler. Multistroke pneumatic airguns need to maintain a film of oil for consistent powerful results.
I also added a Crosman steel breech. I had to rethread the bolt handle, but aside from that, they make a killer breech for the money. It adds a nice heft to the carbine and gives a rock solid scope mount as well. There was a good deal of bolt flip with each shot, so for now, I’ve added a disc magnet below the bolt handle to correct that. This helped to tighten the extreme spread.
Once all the new pieces were installed, performance went up a good deal. With 11 pumps for the initial fill and 8 pumps between shots, it was averaging 505 fps with CPHPs. Accuracy is great when the LDC is properly adjusted and the right pellet for the barrel is selected:
H&N Sniper Lights and RWS Superpoints are nearly neck and neck in performance, easily capable of shooting dime sized groups at 20 yards. Since I am building this for hunting at sub 25 yard ranges, I just placed an order for 1750 of the Superpoints to keep the carbine well fed.
I wasn’t satisfied with the performance, as I’d like to be able to hunt squirrels with this rig. To improve performance, I turned my attention to tuning my free flight hammer. The spring guide and everything attached to it is accelerated with the hammer. The more massive this setup is, the more energy it robs from the hammer. I installed a nylock wingnut for the external stop, cut off the wings, and ground it as close to the nylon as I dared. All excess parts of the spring guide were ground down. Here’s the end result:
Performance has gone up dramatically. It is now tuned for an initial fill of 15 pumps, with 9 recharge pumps between shots. Average muzzle velocity with H&N Sniper Lights is now 553 fps and muzzle energy is 9.5 FPE. This is good enough for my intended purposes. Combining a quick sip of high pressure air with the LDC makes this carbine super quiet.
An even lighter spring guide combined with a 18″ barrel will probably get me over the 600 fps mark. I’m hoping to achieve that with no more than 10 recharge pumps. I’ll continue to document my progress as time allows.