Revolvers don't have safety locks. I still say it was a mislabelled prop gun. Prop guns are disabled from shooting live rounds.

@eschatologyguy Apparently they were using fully functional guns, but with blanks. Steve Turley reported information that they sometimes used these guns for target practice when not filming, in which case they would use normal rounds. This would certainly explain how a normal round could have made its way into one of the guns used for filming. Someone must not have been careful enough to reload with only blanks (?).

I don't know if the guns they used included revolvers, but I agree that revolvers don't have safeties like semiautomatics do. Smith and Wesson makes revolvers that can be locked with a key to prevent them from firing, but that is hardly the same thing.

@KeithThroop the movie was a cowboy movie. Yep, old-style revolvers. Also a working gun used as a prop would not make it a prop gun (just a regular gun used as a prop) just like a working pistol used as a starter pistol doesn't make it a starter pistol. They're supposed to be disabled from shooting live rounds.