I made these high powered SteamPunk cannons using Steel pipe and fittings that were laying around (Free) although if you do not have accese to a steel yard or steel fittings, this project is probaly to expensive for you :(. Just layed out the peises until I liked the look of it [longer barel, large tank/air capacity, and trigger valve position are things to pay attension to], and put the pieses togeter using teflon tape, a vice and a pipe wrench. The main reason to using steel piping it the finished cannon is a lot safer than PVC (at high pressures) and I personaly like the over all look and feel better (a little weight good)
Air Cannon- My record distence was 249 feet (76 meters) with 125 psi at about 45 degrees.
Paint Ball Cannon- Shoots at about 100-150 fps (one round at a time)