You are bring tears to my eyes! My brother and I used to make these cannons and shoot tennis balls at each other. Smashing up model cars was pretty fun too!
In Jr. High School I duct-taped a “tennis ball cannon” to the plastic stock from an NJROTC drill rifle and made a quite effective and “aimable” weapon out of it.
In the days of straight-sided, steel soda cans with welded/soldered seams, the tennis ball just fit PERFECTLY.
Unfortunately it is very hard to find that type of can in the correct size any more. When you do find a straight-sided steel can, it is usually a bit larger (or smaller) in diameter than a tennis ball (that is why we had to use an odd-sized foam ball with the “bean can cannon”).