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digital_blue · June 7th, 2008, 13:27

I just scratch built an MP5 from various parts and I slapped in the mag expecting at least 250-300 FPS from the stock well gearbox. What I got was a less than impressive 170 or so. I opened up the gearbox and it appears that the piston head was very loose in the cylinder and the O-ring wasn't sealing against the sides. Should the piston head be this loose?

June 7th, 2008, 13:27	#1
digital_blue Trader rating Join Date: Aug 2006 Location: In the sticks	How loose should the piston head be? I just scratch built an MP5 from various parts and I slapped in the mag expecting at least 250-300 FPS from the stock well gearbox. What I got was a less than impressive 170 or so. I opened up the gearbox and it appears that the piston head was very loose in the cylinder and the O-ring wasn't sealing against the sides. Should the piston head be this loose?