Genuine antique Colt single action function. There are several features, mentioned singly above.
There is a "Half Cock" position on the hammer that allows raising the hammer a short distance, it clicks, and you lower the hammer into a notch that traps the hammer, allowing the Colt to be carried with a live round in the chamber. Although called the half cock, it is less than a quarter of the way up to full.
This is engineered such that if you pull hard enough to break something, the trigger itself breaks, not the notch. Few men are strong enough to break the trigger in this manner.
Pulling the hammer back with the finger off the trigger, and releasing it before the full cock position, the hammer falls to the half cock notch, and stops.
If the hammer is pulled half way back, the trigger is held, and the thumb slips off the hammer, it falls between the cylinders, and does not fire.
This has been repeatedly reported to be a real early Colt single action, and the features that I have described are included on all the Colt single actions that I have handled. Percussion Colts were not designed in this manner, but they lowered the hammer between cylinders for safety, a position which could break the firing pin on cartridge revolvers such as used in this movie.
Baldwin would have us believe that the hammer fell off the full cock position, and fired the weapon. No, it would have been caught on the half cock notch.
Perhaps since guns still find ways to kill people in movies, we need a law forbidding movies to be made with anything that even appears to be a gun.
The real problem on the set is that there are industry standard procedures that Baldwin has complied with on higher budget movies, that were skipped in this production. He had been taught the rules, and complied, on other peoples dime, but skipped them on his dime.
The gun did not kill the video operator, the people in the chain of custody of ammunition and inspections killed her. Baldwin was just the last in the chain of careless people. He also broke numerous rules, failing to personally check empty (there was no need for any blanks to be in the revolver at that time), pulling the hammer back (single action revolvers are not holstered with the hammer back), pointing the revolver at a human being, and pulling the trigger, whether he remembers that step or not.
Since this event, I have watched a large number of various quality western movies, paying attention to the practices on those sets, and find that when an actor pulls the trigger while pointing the gun, rifle or pistol, at another actor, there is no recoil. The BANG and smoke are added in the lab. Firing from horseback is the same, the horse never flinches, or even twitches its ears. The exception is movies made in the '30's or '20's.
A lot of rules have been created to make movies safe since those early day.