More rifle bores are damaged from improper cleaning than most likely any other reason, and in the case of the muzzleloader, I wore the muzzle almost smooth in a .50 cal flintlock in 5 yrs of shooting and had to cut 6" off the barrel to get back to crisp rifling, so it doesn't take as much as you think. Using a bore guide for cleaning is paramount to maintaining accuracy if you clean regularly, but for a lot of old timers, they clean seldom so it's a non-issue.
Tim