Captchee is presenting a good point on reading a patch. It's a good practice and I ready Poly-patches, sabots as well as cloth patches. It's a way of reading the performance of your patch and in the end, it's effect on the flight of your RB. PRB's are very forgiving but there are always limits and pitted bores is one of them. ....
Each pit is basically a cavity with very rough/sharp edges. Those edges cut into your patches on loading as well as firing. Eventually the pits will pack up with lead and so it goes. When I read my patches and see cutting or any kind of damage. I proceed to determine the cause. Might add that one common cause, is "new" rifling; again, sharp edges.
Not much you can do about the pits but a buddy of mine goes in the smooth's out some of the rough edges with a wire brush with good but not perfect results. ....
Be Safe !!!