I remember reading of one of those Kung Lee movies where an actor killed himself clowning around with a prop gun. During a break in filming, he picked up the Smith & Wesson Model 29 (I think) used in the previous scene, put it to his head and put a bullet through his head. What had happened?
As it was later explained, the gun was used in a close up, showing it being loaded. Dummy cartridges were used for this. The dummy cartridges were removed and blanks loaded for the nest scene. It would have been bad enough had it just been blank cartridges. But a bullet had come out of one of the dummy rounds and remained in the cylinder. A blank cartridge and a bullet equals a live round. Result: a dead actor.
Never, ever, clown around with a firearm. Posing for silly photographs and such can get someone killed very dead.