Wax It
An old trick my dear departed uncle taught me , once you get the rust removed take a black Crayola crayon and rub it vigorisly into the pits and wipe with a cloth cupping the barrel , then wax the whole gun . The wax keeps both air and water off the steel , ergo , no rust ! Can't have oxidation without oxygen ! Plus there is no odor , which we all know is not our friend in the woods !