- 9mm in a .40 S&W
- .40 S&W in a .45 ACP
Here's what can happen when the smaller round ends up in the magazine. The slide goes forward, putting the smaller round into the chamber and probably pushing it in just far enough that it doesn't go off and isn't seen. If the gun is pointed downward, the round just slides out the barrel. BUT, we are all well trained in safety, so when the gun goes click, we keep it pointed down range, and figure that the round didn't load. So, still keeping the gun horizontal, we jack another round, of the right caliber, into the chamber and fire.
The bullet speeding down the barrel encounters the live round. Shortly thereafter, another ka-boom is charged off to a defective pistol!
Jim