I have a MLer that has a regular Blued Steel Barrel that no matter what I do I still get a light brown colored patch from it after it's clean. The Bore is sh shinny and clean that it would blind you yet I still get that light brown colored patch.
If I dont have time to clean right away I Always run a Oiled Patch down the bore, using a alcohol patch dries it up. Also some oils cause a reaction to the steel in the barrel, so sometimes what you think is rust, sin't.
(BP)