Somehow we got hold of some percussion caps from a friend. His dad shot blackpowder in the hunting season, so I guess he didn't notice if his son took a few.
They fit perfectly in the barrel of our air rifle--we'd shoot them at our metal garbage cans. Wow were we stupid...
My brothers had many play guns ala James Bond and the Rifleman that had an air powered cartridge in them.
We would jamb the barrels in the dirt and blast the bejesus out of the "enemy" (usually neighbors or cousins.)
Caution
Do not put light oil in the barrel of an air rifle
[Unless you want more fps]