Idioticgenius made a dual chambered air cannon, 90 psi and an interchangeable barrel – “I started this project when a friend of mine put a Shrader valve on a large rectangular assembly of glued PVC, or what he called an air cannon :-. He used a ball valve and a one inch SCH 40 barrel. We would pressurize the cannon to 100ish psi, and launch anything we could find including rocks, dirt, water balloons, mops, 7/8″ solid oak dowels, and c cell batteries.” [via] – Link.