Barrels should never be cleaned to bare metal until groups fall off. Really good barrels can go 100s of rounds w/o cleaning. As was pointed out cleaning wrecks more barrels than shooting. Nothing with any abrasive ever goes near any of my good barrels. As long as they shoot well, I could care less how shiny they are inside. One of the most famous barrel makers would invalidate his warranty if any abrasive stuff was used in his barrels. Another maker loved those who believed in "barrel break in" as they needed a new barrel far sooner than those who did not break them in.