They make replicas, and they still produce real, single-action revolvers today that are similar to those used in the period that this movie is supposed to take place in, it depends on what kind of gun they were using. But even if they were using a blank firing gun, you know, a prop gun designed to work with blanks. Specifically, there is a possibility that someone could have loaded a live round into that gun, and it could still propel that bullet projectile down and out the barrel towards somebody, even if it's not designed to do that necessarily.