this was it what let me think of a problem of the hand. To be correct - you are pulling the trigger slowly, the cylinder starts to rotate and then, while pulling the trigger further, the cylinder stops anywhere before reaching the end-position (cylinderstop pops into the notch)? -> Did you check movement of the hand with cylinder open? How does it look like? I would disassemble it completely, clean and oil all parts and assamble it again. Then next try.
the problem begins when i put the side plate back on its position.when i run the gun slowly it works perfect. the problem starts when i run it fast enough .