You chrony the shot with the power adjustment wheel all the way in for max preload. and then beack off 1/4 turns while chronying the shots.When you get to about 3-4 turns out from fully in you shoudl start to see a drop in velocity. KEep it right before the drop for maximum efficiency. I use to get about 40-42 full power shots from a 20-22gram fill. Thats 1/2 gram of gas per shot efficiency. I think my hammer spring used was from a crosman model 118 which makes it a little more beefier. Maybe yours is too strong though. Could your exhaust valve spring be too strong holding the seat closed even with a hammer strike?? So when you cock it and fire it the hammer is striking the stem of the valve -right? Check that distance and length of the valve stem to where its suppose to be in the chamber.If the whole thing is short of the striker could also do this. Those barrels like RWS pellets as they are on the large size. Hobbies and Superdomes worked best for me. You should see 525fps with the Superdomes.
This message has been edited by cvarcher on Jun 25, 2012 2:13 PM This message has been edited by cvarcher on Jun 25, 2012 2:12 PM