What type of bow do you have? From what I've been told here by those that know far more than I do about cross bows the Hortons are set up for half moons. It has something to do with the rail being raised at the end. The Excaliburs use flat backs and the rest I don't know.

List what bow you have and I'm sure someone with more knowledge will be able to give you a more concrete answer. Welcome to the forum.