[user104658]

Originally Posted by bitontheslide

When ever a live round gets in to a prop, i would say there must be a deliberate action involved. People are saying things like .... he didn't deliberately do it, because of the actors name and nothing else

Some movies that want to be "authentic" and rely on practical effects use live rounds to shoot objects in one scene, then swap to blanks with the same prop gun for another scene where people will be in the line of fire. So basically (assuming accident) either someone left a live round in the gun from a previous take, or someone messed up when they were loading it for that take and loaded the wrong rounds.

To reiterate again I think in a time of cheap, effective CGI there's no real reason to have live rounds anywhere near a film set - you can get close enough with post processing effects. TV shows for example will unlikely ever be using live rounds, and people just don't notice.