Tennis ball canon. Dad was still at the house, so age ~8.
Saw my brothers do it so my friends and I copied.
Needed four 16 tall boys, two regular cans of beer. These were stronger cans with straight sides with a seam on top and bottom and side.
Use a can opener, cut the tops and bottoms off of four 16oz Budweisers.
Bottom two were 12 oz'ers. Use an awl to punch a hole in the bottom side of the bottom one. A church key hole in the top across from the tab hole.
2nd one up, cut out the bottom with a can opener, and a church key to cut out the top so it had an Archie type opening.
Bottom one was combustion chamber, 2nd one was the throat. Tape them all together, end to end, with duct tape.
Drop 10-20 drops of lighter fluid in the top, wave it in the air for a ten count, stuff a tennis ball all the way to the top of the 2nd can.
Match to the igniton hole, BOOM!. Tennis ball would come down 8-10 seconds later.
When we got more adventurous (or stupid), we would soak the tennis ball with lighter fluid and send it out, flaming.
When dutch elm disease came through and wiped out most of the trees, we would then try to lob the tennis ball down two blocks and someone would try to be there to catch it. IIRC, our aim was never that good, and even if it had been, the ball was way too fast.