I gave up on plugs quite awhile ago. I give the bore a good coat of auto wax and suspend the barrel on a piece of cold rolled rod. A coat of wax after running a couple of dry patches through the bore after boiling every cycle. I can't see any signs of pitting in the bore with a good borescope after the job is done. The muzzle and breech ends don't get blued or browned since it's hard to keep off the wax. It worked well browning a muzzle loader too. I've been using Laural Mt. Forge.

JS