penny cannon

I didn't exactly know where to post this but my step dad told me about this potato cannon that he made all the time when he was young. Well, naturally, I asked him how to make it. I didn't understand it really, but I asked him if he made any other ones. Well he said he made a penny cannon too, but he had forgotten how to make it. Does anyone know how to make one? I don't want it to blow something in half(just an expression). I am for some reason, currently, very interested in steam power. Could he have used steam power? I know times were a little simpler then, although not much, but still, just a thought.

I might be mistaken, but I do believe that you would use a clothes-pin and a rubber band for this, though I forget exactly what was done.