LD, The number one problem I found with rifles in my shop that had lost accuracy was due to improper cleaning.
Yeah in our case with muzzleloaders, leading is rarely a problem and there is no copper fouling, but I have two or three old customers who still remember me as the guy who "saved" their favorite modern rifle, and all I used was some copper removal solution and JB Bore Restore.
Still there were guys who told "the new guy" to buy something huge, and I fitted the guy with something "accurate" instead, usually saving them money, and gave him sighting-in tips...., and these guys always brought home venison even though they were laughed at in "deer camp"....
Now this isn't to be confused with folks who simply want a larger ball going downrange from a muzzleloader. Guys shooting .62 rifles or even a .72, rifle or a .720 ball from a musket, "get 'er done!"
Pedersoli Gibbs Rifle, "African" (.72 caliber)
Because...., That's still a single shot and the shooter still needs develop an accurate load, know the max range for the accuracy, and then choose a stable position in the field when firing at the game to make it all "work".
OH and I've asked a few guys about the really big bores..., several used historic repros, but one guy with a .72 SxS rifle asked me if I had always had a BANG-FLOP result or had I once in a while tracked a deer.? I have tracked two of my deer in the past, but I've done a bunch for friends of mine, and he said, "I've never had to " and winked.
LD