I made it with the PVC I had just to do some testing on different valve desgins and things. The piston right now it is a 3'' end cap. And on the barrel inside is a 2'' rubber coupling(Thanks to Schmanman.)And then the piston seals against it.
For its size it is pretty powerful, it puts holes in 1/2'' plywood with a D battery, and it also brakes apart Way-lights really easy. I am desgining one and going to build a new bigger cannon, I think bigger than anything on the forum, period. It has a chamber volume of 4519.371ci plus a nother 10' chamber, but with a 2'' barrel inside of it.
Here are some pics-

The whole cannon.

Looking in the back at the barrel with the rubber coupling.

Looking in the back again with the 3'' end cap.

Looking at the front, the barrel is flush with the bushing.

A pic of the modded valve with the 3/8'' ball valve.

Were the valve connects to the end cap.

A pic of the PSIG and the male quick connect.

A nother pic of the valve.

A pic of the back assembly.
If ya got any questions, ask.
Here is the video#1!!
