We called them Polish cannons. Five pop cans, when they were tin, top and bottom cut out of four, a hole in the bottom side of the bottom one. Taped together, lighter fluid and a tennis ball as Gary mentioned.
Squirt fluid in it, shake it a bit, stuff the tennis ball in the top and light it in the little hole at the bottom.
It would shoot that tennis ball out of sight!
I was in the sixth or seventh grade and my teacher heard me talking about it. Asked me to bring in in and demonstrate it.
We went out to the football field and I lit it off. He had me explain what and why I was doing. Lit it off one more time. Got an A for that!
Cant imagine what they would say now if I brought one to school.