They don't (and I'm an actor who's been on stage and on movie sets for over 40 years). Which is why this was particularly tragic, because it should have been avoidable. Gun safety 101 says "always treat every weapon you're handed as if it's loaded!"Not any knowledge of movie rearms.... but are there "prop" revolvers with functioning/rotating barrels that have "fake" (not blanks) bullets/casings permanently in the chamber for the realistic look when filming up the barrel of the gun, or for closeups? In other words, why do any film/tv productions nowadays need to use real firearms even if they "only" have blanks?
Baldwin, however, is a notorious anti-gun zealot. I doubt he was ever taught the proper way to handle a weapon, or ever attended a gun safety class.