I would go with the .54 caliber. Since the rifle will be shooting only round ball for the most part, I would try to get the hardest hitting one of the two. I notice people claim the .50 caliber to be easier to find supplies for. That might be true when your in a pinch, but I am well stocked and prepared when ever I go hunting, so supplies are not a problem. Many on line stores carry everything you will need. I have a .54 caliber and a .50 caliber, and they are both excellent rifles and shooters. I just like the heft of the .54 caliber more. Which ever you choose, you will be happy with the Lyman Great Plains Rifle. I have been trying to talk myself into one, but you know how it is when you have "too many" already (there is never too many in my book). Good shooting, let me know how it shoots......