Sounds like your getting a lot of back pressure. Make sure the valve is in correctly and make sure the velocity isn't high (under 300 fps). Also check the stricker spring and the rear bolt bumper. The rear bolt bumper is on the rear bolt plug. The bumper is there to prevent the bolt/striker from moving too far back when the marker is recocking. Also visit the Brass Eagle Owner's Group http://pub101.ezboard.com/bbeog
There is a modification posted there that will help the bolt/striker rear travel. Its called the "eraser mod" or something like that. Check in at the Raptor forum or check the Mod/Tech archive forum for the directions for this mod. Good luck and be sure to post back here to let us know how it goes.