I am not going to recommend a specific rifle. Just a couple things to consider concerning caliber before making your purchase.
I hunted a lot of years with a muzzleloader. Most of my hunting buddies hunted with them as well. I would recommend a 54 over a 50 or 45 caliber. All work well being effective. The difference is the blood trail. I have seen deer double lunged on several occasions with a round ball. Then run off with not much of a blood trail. The lack of blood is often very discouraging, although a fatal hit was inflicted. All things equal, a 54 leaves a better blood trail than either a 45 or 50 caliber.
If you wish to hunt elk someday with your muzzleloader, I would recommend a 54. With muzzleloaders, the velocity of your round is limited. Weight of the bullet becomes much more important. A 54 will you give you a decided advantage, in my opinion, over lesser calibers. The shoulder on a mature bull is much tougher than a shoulder on a 150 pound whitetail. Heavier bullets hit harder and tend to penetrate better.