[bluesea112]

The only way to permanently stop rust is to treat it with ospho, which is phosphoric acid. You can buy Ospho at any hardware store. It will be a green liquid or greenish blue liquid. Use steel wool to remove as much rust as you can. Then pour Ospho on the metal. Let is sit on the metal for several minutes and then pour some more on the metal a second time. Let the second treatment sit for several minutes. Any rust that is left on the metal will turn black or completely disappear. Now rinse the metal with extremely hot water and let dry. You can lightly rub steel wool over the metal one last time, but try not to remove the black coating left by the Ospho. These black areas help to protect the metal and will blend in once you apply cold blue. The last step is to apply cold blue. Your gun should never rust again.

The reason Brownell's cold blue works so well is because it contains Ospho (Phosphoric Acid). By using straight Ospho first, before using cold blue, you get a little better protection.

Phosphoric Acid actually changes the chemical traits of the metal surface to make it immune to rust formation. The only purpose of the cold blue is to turn the entire surface black so all the metal is the same color. The cold blue does not protect the metal, as it is simply a colorant. The phosphoric acid treated metal can be left just as it is without being colored or painted and it will never rust again.