Repairing the bluing on a gun barrel protects the metal from rust and scratching, and helps reduce glare when shooting. There are two types of oxidation processes for bluing a gun. The "hot" process uses nitre bluing salts and requires liquid heated to 343 degrees C to activate the salts. There are also hot bluing solutions that require use of a blowtorch or other heating device to process the bluing. The "cold" bluing process is more common among gun owners who can easily return their barrel's blue finish without the need of a gunsmith. Proper metal preparation is key to successful bluing repair.
Use 600- to 1200-grit fine sandpaper to remove pits and rust from the barrel. Sand in the direction of the tooling mark on the barrel. Remove all rust from the repair area.
Degrease the barrel with acetone or denatured alcohol. Wipe dry with a soft, clean cloth.
Apply cold bluing solution to the barrel with a soft clean cloth. Focus on 1- to 2-inch sections at a time. When the finish reaches the required level of blue, wipe the area with a clean dry cloth. The newly blue finish appears dull. Buff the area with No. 0000 steel wool to blend the bluing with the rest of the barrel.
Apply gun oil to the repaired area, then buff with a clean, dry cloth.
The key to successful bluing is preparing the metal. Use quality gun oil after bluing to stop the oxidation process.
Wear protective gloves to keep handprints off the gunmetal and to keep your hands safe from bluing solution.