My dad did this type thing when he was young. He found a picket in the back yard fence that had a knothole that was just the size of a 12ga. shell, emptied the shot out and forced it into the knothole. It took a long period of target shooting before he actually hit it, splitting the picket.
When I was a little kid, my best friend lived next door.
Him and his neighbor friend took to shooting .22 shorts with their bb guns until his friend got hit in the knee with one of the flying cases.
Like you said, that's how people get hurt.