Getting piston to work

[Shrimphead]

I am working on a 3" piston cannon. I made foxx's 3" piston, just a little differently. The problem is that the piston won't ever seal against the barrel. I think that it's just because the piston won't slide easily. I think to fix this I need to deepen my or-ring grooves so it isn't so tight inside of the chamber. Any other ideas?

[saladtossser]

instead of letting it seal on the barrrel, put a coupling on the barrel and let the piston seal up against a pre manufactured smooth surface

[Shrimphead]

The edge of the barrel is pretty smooth. My grandpa cutted for me on his miter saw. Just a quick drop of the blade and it was cut straight and smooth. Also, I just realized that if I put a coupling on the end of the barrel, the equalization holes would be covered and the main chamber wouldn't fill. But thanks for the idea, any others?

[schmanman]

build this piston.much easier. and add the rubber coupler http://www.spudfiles.com/forums/viewtopic.php?t=1666&

[Shrimphead]

I need a 3" piston not a 4", but thanks.

[schmanman]

oh,I thought you ment a 3" diameter piston for a 4" valve,sorry