Ok, try the semi-chrome stuff, if that does not help, get some "bar keepers friend" powder (or cameo or similar) make a paste with liquid dish soap. This is where you will want a once fired shell soldered to a rod. use slow speed on a hand held drill ( low or medium on a cordless drill is about right) and burnish the chamber with the brass shell, and home made polishing compound. This will remove high spots, but will not remove metal. Clean up is easy, and no you do not have to flush it with water.