If you research caplock rifle target shooting from the 1800's, you'll find out that not many were shooting bores as large as a .50, most likely because it's quickly tiring, and even more likely, more expensive than a smaller caliber.
The target guns almost invariably had bull barrels.
.40 & .36 (which can use buckshot) calibers were lighter on both shoulders & wallets.
Some today use a .32, but that bore is too small for my fat fingers to handle easily. YMMV.
Holy Black & lead PRB's (patched round balls), in a slow twist barrel, is the path to accuracy.
I highly recommend a read of "The Muzzle-Loading Caplock Rifle"
, by Ned Roberts - it's a classic book that will edukimate anyone interested in shooting targets with a frontstuffer.