SpudFiles

does the piston have to seal on the way backward when it's in it's farthest back position or just against the barrel in a piston QEV design?

i would but you dont have to be as careful as the barrell sealing part. you also might want to add a spring behind it too because i have heard the impact of the piston slamming back can damage the gun.

It only has to seal against the barrel. But ya, definately put a bumper or spring or something behind the piston.

wouldnt a seal on the back increase preformance though? if it didnt seal when it slides back then air could escape around the piston instead of going out the barrell. it wouldnt be that big of a deal but it seems like it should seal both ways.

Not really, because your piston should already have somewhat of a seal against the wall of the chamber, so it'd be easier for it to go out of the barrel.

well thanks for the help guys. i found some neoprene and made it seal in the back. What I did was just have the rear pipe be the bumper and the sealer for the piston. I reinforced the rear pipe with a screw through the fitting. it's definately not going anywhere. I hope it has a long life

i'm waiting on a valve but as of now i can move the piston by lightly sucking and blowing. (sounds gay but honestly i'm not)