Good ears! Hopefully the shooter already knew something was amiss. I had that happen one time several years ago (maybe 20), at deer camp. Everyone was enjoying plinking with my .357 Marlin levergun, (using my reloads). Another fellow was shooting it when I heard only a "POP", not a "CRACK". I did the same thing "STOP-STOP-STOP!!!

Thankfully he heard me and had already started lowering the gun. But I didn't know if he was about to rack in another, or it he knew something wasn't right. He knew. I learned to slow down.

Would have been worse I asume with a .45 handgun than that rifle, but wouldn't have done either gun any good, possibly shooter as well. Three Cheers to the S.O.!