I can't believe that my boys and I are the only ones who have made compressed air cannons and fooled around with different configurations and such, so I figure I would start a thread on the subject. Tonight I get home and the boys are working on a project we started a few weeks ago. The air tank is an old CO2 extiguisher, godd for 2000 PSI, we have added a gate valve, a fill valve and an adapter that we can thread on different barrels to. Currently it has an 1.25" schedule 80 PVC pipe for the barrel (all other pressurized fittings are brass or steel). The barrel is 10 feet long, which I think is too long and we are losing some velocity out of it but the boys refuse to cut it. The projectile started out as a standard glow stick. It doesn't go too far by itself (out of a smaller bore) so we taped a broken arrow with the fletching on it to the back. That did OK, but only made it about 200 yards. Tonight, they had made a wooden head out of a closet rod, it is about 3" long. In one end they drilled (on the lathe) a hole for the glow stick and the other end got a hole for an arrow shaft. This sucker went exactly 321 yards 9 as measured with a Leupold laser range finder). We retrieved that and put the wood plug on the lathe and made it more of a teardrop shape for aerodynamics. First shot the thing came apart, but we found all of the pieces. We didn't get a second shot because mom called us in for dinner. Oh, and all of this is being done in the dark. Its much easier to find the projectile when we use a glow stick in the dark rather than watching for it in the daytime and calling the boys into it from the house (we did this with tennis balls- lost a couple). Here is a pic of the last configuration.