[Doug G]

I've used a 3" x 4 foot barrel to launch 4, 1 lb water balloons, all at once to a distance of at least 50 yards. Using similar methods mentioned here but for storage tanks we use TWO scuba tanks, pressurized to about 80 psi and the only PVC part we use is the 1" Sprinkler valve. For lubricant I've found the best solution was to dump about a half gallon of water in the bottom of the barrell and then place water balloon(s) inside. When the cannon fires the incompressability of the water around the water balloons keeps them from popping on the way through the barrell. Using this method with LARGE storage tanks and a long barrell results in some incredible distances. The first time we tried this at my house, I figured the balloons might make it to my neighbor's house across the street (he was in on it), instead they flew over his tree, over his house, over the house behind his and hit in the street in front of that house. Incredible. Unfortunately the canon now sits on top of a robot and I don't dare let the student's launch water balloons until it's adequately waterproofed.