SpudFiles

This piston can be made to any size because of the pvc/material disks that can be cut how you like.The o-ring is placed between the disks but supported by a smaller disk. The diagram is self expanitory.

*sorry,I forgot to add the rubber bits

Nice, i will use this design if i ever make a piston cannon, so simple yet so
effective.

I really hate fiddling with o-ring grooves I will make this today sometime.