I started shooting black powder rifles in Dec. of 1972, with a .50 TC Hawken. By 1974, I had learned to re-crown the barrel, use .022" denim and .005" undersized ball, 2F GOEX powder and it stopped "fouling".
No barrel nor rifle or smoothbore I have had since and there have been a LOT of them, has ever "fouled". All could be shot all day without swabbing, wiping or in any way cleaning the bore, as it was cleaned each time it was loaded, just as Ned Roberts noted in "The Muzzle Loading Cap Lock Rifle".