A dark bore may shoot well. It is never very gratifying to clean.

Patches tend to come out black & green forever. It is hard to know when to quit.

IMHO - 'Wire-Wheeling' with a drill powered cleaning-brush and grinding compounds may get things shiny, but, introduces lots of irregularity to the bore and probably worsens accuracy.

Lead Lapping, as some have suggested, has been a long used technique to improve pitted bores. It does change optimum bullet diameter.