I agree with pvc arsenal. You should make the chamber out of pvc and buy an air compressor. My pneumatic pb gun shoots paintballs straight through 1/2" plywood at 100 psi and is very accurate with iron sights. I would put a picture of mine but i cant upload pictures. Nice gun though.

It looks almost exactly like my pb rifle but i used 1 1/2" for the stock. What kind of barrel did u use?

I have seen numerous bbmg guns but i dont exactly understand how they work. Could someone draw a diagram or something?

I use 3/4" pvc for my paintball rifle barrel. It seems to work fine with decent paintballs.