JB non-embedding bore compound sure comes out black on my patches when I polish a bore with it, just like it does with Flitz, Maas, Simichrome and USP paste, it sure as heck does remove a very small amount of metal from the bore, they're all very mild abrasives. If they didn't remove any metal, what turns the patches black, and don't tell me it's carbon fouling, this is from new bores!!
I just polished the chamber on my 7mm-08 barrel, finally got it fitted to a frame, JB turns the patch black just like any metal polish, although maybe no as fast. It doesn't take long with a patch wrapped mop on the tip section of a 3pc cleaning rod chucked in a drill, which is SOP for me!!
Tim
SOP = Standard Operating Procedure