I shoot a LOT of blackpowder muzzleloaders. I don't have much interest big bore fowlers myself. My personal choice is a small caliber Southern Mountain Longrifle. That said..Mike did a GREAT job creating a really nice historic piece in that one for you.
Last September I competed in a "Woodswalk" competition at the NMLRA National Championship matches in Friendship, Indiana.
A fellow in my group was shooting a 62 caliber Fowler, built for him by Tip Curtis. I don't remember the details of his load, but I got a whole new respect for what a
well developed load and a
highly motivated skilled individual can do with roundballs loaded in a
smoothbore at longer ranges that day.
He was ringing the longer range gongs like Cathedral bells..!!
Good Luck with that one...Once you find the "right" combination, I'm quite sure that Colerain barrel will certainly do it's part, if you do yours.