When I was just a tyke, and society was not so "correct" every kid had a few cap guns. And caps came in a few different styles. Roll caps, perforated roll caps, stickem caps and flat sheets of caps, that could be torn off individually like postage stamps.
For 20 cents we could invest in days worth of noisey fun and games. However, sooner or later, we all discovered that instead of one lame pop, we could combine the effect of several caps at one time by overlapping them and hitting them with a hammer. And one day, at about age 11, we discovered that a tightly wrapped roll of caps could launch a rather sigificant boom, if stuck just right with a 10 pound sledge. My buttocks still warm at the memory of my father discovering that we had broke a corner off the concrete front steps to the house.