The so called "Charcoal blue" that Uberti uses is nothing more than nitre blue and abrasion and stronger acids will strip it since it is very shallow. Using any good gun oil should be fine and clean the bore as usual. Personally, when I encounter these guns after the nitre blue wears off in short order, I then have those parts slow rust blued as it looks period correct and is the most durable real blue finish you can put on a firearm. Eddie Janis of Peacemaker Specialists uses this on Colts.