is this just for target shooting or hunting?
I'm a traditionalist, using a 50 cal T/C New Englander sidelock, for target shooting at the club and for deer hunting.
If just targets then a .45 caliber is easy shooting, but the .45's are scarce.
.50 caliber is next up and good for both hunting & targets.
Action is open as you can get the modern style in-lines or the sidelock.
little more info be helpful.
Call T/C arms and ask for a free copy of the muzzleloader manual, its a good read and explains the aspects of black-powder arms.