if the gun has seen alot of use replacing the Orings in the gear box may help bring up the FPS. Using a nozzle with an O ring also may help. You can also try using heavier bbs like .25 .28 see what that does for your fps. You could also add a another hole to your piston head. I picked up an Oring for my cyma piston head at ACE hardware and it brought my FPS up from 250 to 285.