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 waitin...

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?