Tragedy nearly struck during rehearsals for an amateur production of John Steinbeck's Of Mice and Men in Sarasota, Florida. The actor playing George shot the actor playing Lennie, as per the script, but this time the gun was real and so was the ammunition.
It was an accident, and luckily the bullet didn't penetrate the actor's skull, Incidents like this illustrate the very real need for anybody involved in theatre to really know what they're doing before trying to use potentially dangerous props or equipment.
Here is an article on the incident in Florida.
Here is a good article on using guns on stage.
Below are some books on Stage Safety: