Trebuchet03 writes “A pneumatic cannon for launching plastic soda bottles…. or ketchup packets. Almost all parts can be obtained from home depot and probably any local hardware store with a plumbing section. Bigger is cool looking… But not always better. I have found smaller more robust designs to be far more fun that the gigantic heavy cannons. I can recharge (with a foot pump) and reload in less than 30 seconds and hold this thing much easier than its heavy breathing counterparts. Other than this design, I no longer build using PVC as it does fail catastrophically.”Link.