About 20 dollars of PVC and a grill ignitor put together to launch a potato at high speeds in excess of 300 feet. Sounds like a gunshot. Typicly made by bored, immature teenagers, but is incredibly fun to create/play with. If you shoot a potato it'll scare the shit out of everyone within 500 feet of you.
Last friday night some nerdy freshmen made a potato cannon and shot my front door. I then went outside and ran them over in my ford bronco.