I put a new exhaust valve in my Eun Jin Sumatra .22 PCP air rifle today. The old valve was leaking, I tried to machine one myself from Delrin, which worked, mostly... It held air and fired, but it was too light and I got the dimensions slightly wrong as well, so shot power was very inconsistent... In any case I ordered a new factory valve, installed it and sighted the rifle back in. These were my best groups:
I’m leaving the scope dialed slightly high, as I sighted it at middle-red on the power wheel (I know that makes no sense unless you own a Sumatra, but it’s slightly over half power), which is throwing those 21 grain Baracuda Match 5.52s at 1050fps, and the ~16 grain JSB Diabolo Hades at about 1180fps. I often hunt with a 26 grain slug, or turn the power down a smidge to get more shots out of the tank, so this is a reasonable POI for these pellets at these powers... Very “middle of the road”
I'm quite proud of that Baracuda group.