is ur bolt facing down, etc?
also, do u have an evo length bolt in a reg cocker?
did you completely tighten the pump rod thing at front?
any leaks anywhere on marker?
also, if you hold the pump handle and keep it held back when u try to shoot, that could cause problems
can't really think of much... i'm prolly not the best person to be tryin to help you out, but i'll try =P