This is a picture of a Capewell horseshoe nail. You can go down to the feed store and buy one of these today. Horseshoe nails have been the same shape for many years. The head is tapered so that when it is seated in the shoe, and the shoe wears down, the nail continues to hold tight. The tip is beveled so that it will come out of the foot. The nail is designed so that the horseshoer can aim the nail to come out where he wants. The shoer will start the nail at the same angle as the hoof wall, and if you were watching, you will notice that he starts out tapping the nail, doing that he's aiming where he wants it to come out of the hoof wall, so it usually goes, tap, tap, tap, tap, whap, the nail is driven in and comes out of the hoof wall, and eventually all four nails come out at the same height and in a neat straight row. So you can't really date horse shoes by the nails, nor by shape, nor style, because a horses foot hasn't changed in hundreds of years. Hand made shoes are still made today exactly the same way they were, dating is pretty much a scientific wild guess. If there is other datable stuff found with the shoe, that's probably the best, most accurate way to date it.
