Tennis Ball Cannons
At this time (twelve years ago from 1988) most soft drink cans were rolled tin rather than the molded aluminum. We would cut the tops and bottoms off of a bunch of them and tape them together with duct tape, forming a tube of two feet or more.
At the end we would tape a can with the bottom intact, more holes punched (with a can opener) around the top, and a small hole in the side at the base. We then fastened this contraption to a tripod so we could aim it reliably. Any object that came somewhat close to filling the tube was then placed therein.
In the shop, we used the clock as a target and an empty plastic solder spool as ammunition, with tape over the ends of the center hole and sometimes filled with washers for weight. When taken to parties or picnics, we would use whatever was handy. Hot dog rolls or napkins filled with potato chips provided spectacular entertainment.
Once loaded, a small amount of lighter fluid was poured into the hole in the side of the end can and allowed to vaporize for a few moments. The "fire control technician" would announce "Fire in the Hole" and ignite it.
BOOM! Whoosh! The clock never worked after that!
Our version of the potato chip cannon, originally designed around the Pringles potato chip can, was built similarly. Ours used coke cans, six with the top and bottom removed, and the seventh had Bottle opener holes all around one end, the top of this can was covered with a grid or piece of wire screening to keep the tennis ball from falling all the way to the bottom. This was spiral wrapped with at least two rolls of duct tape.
A wooden shoulder rest and forward hand grip was taped to the tube. For ignition we used lantern batteries to a model-t coil, actuated by a push button on the hand grip. A fresh wilson tennis ball was stuffed all the way back to the grid, and a drop or two of lighter fluid was dropped in one of two holes in the end. The ignition wire was poked through the other hole.
We would then lie in ambush, waiting for somthing to move. When fired with the proper air/fuel mixture, a satisfying thoomp! At maximum range the ball would travel about 100 yards with a 45 degree launch angle. Closer up the ball would leave a welt on an warring opponent. When launched at a moving car the thud as it hit the door would generally rattle anyone inside. Luckily we never completed the one that shot golf balls.