My opinions on cleaning a black powder, muzzleloader bore should be weighed with the fact that I have been getting serious about this activity for only a year and have had traditional muzzleloaders for a little over 2 years.
That said, I have seen some rifles with minor, but visible pitting in the corner of the rifling grooves. These are rifles owned by people who use only patches during the flushing of the bore (and some with pinned barrels that don't get the flushing). That pitting, however minor, concerned me enough that I use nylon, pistol bore brushes to get the crud out of the corners and crevices. Of course it took me one experience with a bronze bore brush to shift to nylon only!! My dogs learned an entirely new vocabulary during that activity.
The nylon bristles change direction in the bore pretty readily, so I don't have much concern with using them.
I put the nylon bore bushes in the dishwasher between each use, otherwise I am just putting crud back into a bore if I use a dirty brush.
After shooting, I put a toothpick in the touch hole, pour a water, dish detergent and Simple Green (just a few drops) mix in the barrel, let it sit for a minute or two, then remove the toothpick and run a patch up and down the bore, driving the water out the touch hole. I will add more of the mix and do that a second time until the water runs clear from the touch hole.
At home, I put the rifle in a padded carpenter's vise, add some of the mix, and use the clean nylon bore brush. The water that comes out looks dirty again. (It was tough decision getting that vise because I told my wife I have no vices.
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Then I run several dry patches through and finish off with "*Fluid Film" corrosion protection on a patch and run a few more dry patches so that only a residual film is left in the bore.
Then, after all that work, I take a nap.
Ron