Most gun barrels are coated in a bluing agent that turns deep blue or black. This finish protects the metal surface from water, rust and scratches. After years of use in the field, the surface of a gun barrel will become worn. It's also possible that bluing will rub off in some spots. To refinish a black gun barrel, you must first remove the original finish.
Rub the entire metal surface of the gun barrel with a piece of fine-grit steel wool until the remaining finish rubs off. This may require vigorous scrubbing for several minutes.
Apply a degreaser, such as shellite or acetone, to a cotton rag.
Rub the degreasing agent on the barrel to remove all oils from the barrel's surface. Wipe the barrel dry with a clean edge of the rag.
Apply a gun bluing agent to a lint-free cloth and gently rub the solution evenly across the entire surface of the gun barrel. Rub in a circular motion to ensure an even coat. The barrel will begin to turn blue, then dark blue, and then black. The richness of the color depends on how much solution you apply. It's up to you to decide what color works best for your firearm.
Apply gun oil liberally to a cotton rag and rub the oil over the entire surface of the barrel. Make sure to saturate all areas of the metal with gun oil. Allow the gun to sit overnight with the oil on the metal.
Rub the surface of the barrel with an oiled rag 24 hours after you applied the first coat. This will remove excess bluing and polish the surface of the newly colored barrel.