We have squirrels, grouse, ravens, Bald Eagles, a few bunnies and moose all around our place. I don't shoot 'em because having them around is better than the neighbors dog. House cats are fair game. The most lethal predator on the planet.
When I was taking my state-approved black powder qualifications, we had to use Knight in-line guns. We were not even allowed to bring our side-locks to the range. We had to clean them out at the end of the day and I still had no trouble cleaning it out and I learned about how those things are put together. I still like my side lock CVA Mountain Rifle. I have the pride of knowing I built it and I love how accurate the thing is.
This "crud ring" you guys are talking about......Must be from pellets and always being at the same spot. I don't seem to have one. But I always use a stainless steel brush and scrub hell out of the bore all the way to the breech plug. I wrap a patch around the brush too. I do this until it is clean and smooth, then run a few patches with some Bore Butter down to give it a light coat. Seems to do the job for me anyway. Then it goes up on the wall where it can look pretty and add to the ambiance of my small home.