I recdntly did a gas nitro piston conversion to my benji as well as sanded and polished my gas spring and piston. Im noticing after about 10 to 15 shots my gun drops from 750 to like 400 next shot will be like 580 then back up to 745 then down to 450 like the fps is all over the place. Replaced all the seals with new ones. Changed and tested breach seal and i know the loss of fps is 100% not from the breach. I also swaped the piston with a diffrent one and it still did the fps drop. Which leads me to think its the gas spring or the lube. I switched to a molly lube and its still doing the fps drop. I even changed to the whole compresion tube. So im thinking its the gas spring does any one know a way i can test the gas spring or have had this problem or know of another cause for the fps drop?