In the movie "Shane", Alan Ladd carries an SAA but in the shootout in the bar the SAA mysteriously vanishes and a DA revolver (Colt New Service?) appears. Ladd was a small man with small hands, and he just could not fire a SAA as fast as the scene required.
Today, of course, they would probably not use a real gun at all; the "back room boys" would add the flash and noise to the digital master. In fact, after a couple of movie set tragedies, the insurance companies have pretty well stopped use of real guns and blanks on movie sets.