I imagine its a prop gun. First, for a set of a TV show, there isn't a need to have real guns on a set, when its a gun who's duty is to hang above a fireplace. Second, the foreend of the stock appears to be very thin, to where it could not accommodate a ram road. The forend is no wider than the barrel past for the for end, judging by the photo. If its percussion, it should have a ram rod store spot underneath the barrel. Also judging by the lock plate and trigger, it almost looks like a toy, more so than an actual gun. The lock plate is reminiscent of the ones found on zinc / pot metal "percussion" cap guns, from years back.
Winchester 73, the TFL user that won the west