Its a western right? One would assume they were using revolvers. Unlike semi-auto pistols which require a certain amount of force to cycle a revolver doesn't require that. A semi-auto that is a "prop gun" has a restricted barrel because when a blank is fired it won't cycle the action. Some revolvers are props with restricted barrels but others aren't because they are used for close up shots where the camera can see down the end of the barrel. Thus it might have just been a gun. It's just got blanks in it. You can put live rounds in it and shoot someone just like any other gun.

Most people don't get this but many of the guns on movie sets are quite dangerous. I can't remember which actor it was but there was an actor killed once because a piece of debris from a previous scene got into the barrel of a prop. So when a blank was fired in it doing the next scene that debris acted like a bullet and hit the actor he was pointing the gun at.