My G3 was shooting at 280 fps stock (I put a full cylinder into it because the gearbox came from a G3-SAS) I put an SP120 spring in it and the fps decreased to 260. I have a really good seal in the cylinder, I just re-took it apart and tested it, there are no air leaks and i can only compress the piston about 1/4 of an inch when I cover the nozzle. I am not sure what else is wrong with it. Any ideas would be welcomed because this is my primary weapon and without it I would have to run around with a pistol... thanks.