10' Air Cannon

Well, I figured I might as well start this blag off with a quite literal bang. This is an air cannon I made about a year ago that fires projectiles at 800 feet per second. The barrel is 10' of either 1.5" or 2.5" PVC pipe and the chamber is a total of 10' of 4" PVC pipe (All the components on the cannon are pressure rated). This cannon doesn't use a ball valve or any other slow opening valve to fire, instead it uses a chamber sealing piston valve to quickly dump the air pressurized  to 120 psi in the chambers out the barrel. The effects of all this energy imparted on a tennis ball or arrow are quite substantial, as evidenced by the video below.(+1 Internets if you caught the XKCD reference.)