I have this ring around the inside of my barrel near the breech plug where the powder/bullet sits. I have only shot BH209 through my gun since buying it last year. I have swabbed with T/C bore cleaner and Hoppes #9 and scrubbed at it with my bore brush without any success in getting it out. Could it be circumferential pitting or is it just crud that I can't seem to get loose? Any tips for getting rid of it would be appreciated. It's driving me crazy!