I had one of those "starter pistol" that you could buy almost any where back in the 1960's. Took it and opened up the cylinder so it would accept .22 pellets. Most of the pellets would get stuck in the barrel because the nose of them were too thin. So then we started pushing a .177 pellet into a .22 pellet base to reinforce them, they always made it out the barrel.I used to shoot .22 crimp blanks with a Crossman .22 pellet. It would penetrate about 1" into a 2x4. Good rat round.
Then there were the ZIP guns.....