If your looking for a percussion cap in .45 or.50, I would look into a Thompson Center Hawken. Although, they have recently been discontinued, I
assure you that it was not a quality issue. I have just finished reconditioning mine and it looks and shoots great. I use round balls and maxi balls in it. I have this muzzleloader for 30+ years and I also have a T/C 209/50 and I'am very happly with both.
Currently in the process of gathering parts to put together a .45 or .50 Hawken Flintlock.
The 209/50 has a 1in 28" twist and the Hawken has a 1 in 48". I would be happy to help you gather any information you need to make a decision on what to purchase.