My close call was having reloaded 10mm and took the batch out shooting. One of the taper crimps wasn't tight enough and the hammer fell when my much younger friend pulled the trigger...click, but no bang. Naturally, he racked the slide to extract the 'dud' and chambered the next round from the magazine. When he did, an empty shell casing flew out. He cleared the pistol and showed it to me. There was gunpowder everywhere inside the gun. I tried to blow out the powder, seated the magazine and chambered a round. I was just preparing to fire, when it hit me...why an empty shell casing?
I pulled the magazine, cleared the chambered round and visually inspected the throat. Guess was was staring back at me?
Another one I heard of from a friend who was at a pistol comp. Some dude was firing a .45 with his reloads. He also reloads for his .40S&W; managed to accidently slip a .40 in with the box of his .45s. He was chatting with someone while loading his magazine and didn't notice the .40 snuck in with it's bigger brothers. While firing under time, he had a misfire, racked the slide to clear and fired again. Of course, the diameter of the .40 set the primer too low for the firing pin to strike it, but it struck the upper rim, stuffing the live cartridge into the throat. When he racked it, no round ejected, but he was in a hurry.
Needless to say, that next shot ended his set.