The frist mention that I heard of a potato gun was a tennis ball cannon built from PVC. A classmate was talking about a home-made gun that her dad had built. He used it to shoot tennis balls 100's of yards for entertainment at family reunions and such. The father of another close friend was reminiscing of his younger (more foolish) days, and told of a tennis ball cannon that was made from old steel cans. The ends of the cans were cut out & it was taped together with duct tape. The crack-pot design used gasoline as a fuel; a lit match as shoved into a hole in the base of the home-brewed mortar in hopes that it would ignite. Obviously this was extremely stupid AND dangerous.
Albeit almost all of us have heard of these kinds of home-brewed cannons, there are untold numbers of horror stories of when things go wrong. I want to make it known that a lot of us spud gun enthusiasts despise the outright idiots that do stupid things to give our hobby/sport a bad name. For every horror story heard, & told there are twice as many times where spud guns are used in a safe & responsible manner. The foolish actions of a few have helped to create the bad image generally associated with spud guns & spud gun enthusiasts.
This brings us to the next topic is Safety but first a quick disclaimer.