I have just tested three CFX/CFR rifles all using JSB .177 pellets at 8.44 GNS.The rifle holding a Custom Airseals ram clocked 757 fps. The one with the standard CFR ram clocked756 fps and the one with a lower powered Challenger ram clocked 690 fps.I don't know if this helps much as all have shortened barrels and have modified piston to use Weihrach piston seals. I cant give any numbers from months or years ago because I have only just bought a chronograph.I wonder if the rams lose a bit of pressure over time.
Leave the transfer port alone messing with it usualy turns out bad. Don't Ask me how I know!Sounds like your piston seal is a little tight. No big deal. Either resize it or just shoot the snot out of it. It should loosen up after a few hundred shots.Frank
Sometimes it does not take much to go from snug to loose.What chrono are you using and at what distance?
Quote from: Airnut on May 19, 2022, 05:30:31 AMSometimes it does not take much to go from snug to loose.What chrono are you using and at what distance?crony f1 & point blank.I am getting 700 fps with 8.3 gr Superdome pellet.The o ring on the breach is leaking some.blows tissue off .I tried a looser piston seal but actually lost 50 fps so went with back to the snug fit