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A Brief Overview of Metal Finishes for Keeping Guns from Corrosion

By: Josh Wayner

Weapons are interesting objects in that they are expected to endure strenuous abuse and still function over and over as if they were new. The act of firing a gun essentially causes what could be described as damage to the weapon. The high pressures, heat, and friction will eventually wear out even the best guns.

Rusting and rotting are two of a gun’s favorite things to do. They are in a constant state of wear and erosion. Across history, many efforts have been made to create guns and other weapons that resist damage in the course of use. Swords would have been carried in their scabbards with a coat of oil on them to prevent rust. After a battle, the blades would have to have been cleaned and reoiled, as blood contains iron and oxygen, the basic parts of iron oxide, or rust.

The paradoxical element of shooting is that you are introducing something to a gun’s surfaces that will cause corrosion. In the old days of black powder, an especially dirty and highly corrosive material, the shooter had to maintain his weapon with great care. The residue of fired powder left a thick, caked-on and highly porous layer that could easily absorb water in the air and cause terrible corrosion because of the salts present in the powder. To wash the salt out, gun owners would pour hot water directly down the barrel, but this process would leave the metal vulnerable to rust. The bore and metal surfaces had to be mopped with oil or grease to protect them.

With this type of cleaning and firing cycle, one would expect that a gun would get worn out in a matter of hours, not the hundreds of years they can last. So how does one go about making a reliable weapon in a world full of corrosive agents, salt water, rain, hand oil and sweat, blood, carbon buildup, and harsh cleaning chemicals?

It may seem counterintuitive, but the way we can halt rust and corrosion is by controlling the rusting and corroding ourselves, which is where the process of browning and bluing comes in.

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Browning
Browning is an old technique that essentially involves the forced and controlled rusting of gun parts to generate a protective layer of rust that deters other corrosion. It is not used much today, because it doesn’t add a very deep coating, nor does it add any surface hardness to the metal.

Bluing
Bluing is similar to browning in that it is also a form of rust, but it oxidizes black or dark blue instead of red or orange because of differences in the process. Bluing is an extremely common type of modern firearm finish, and it provides a great looking product with good durability. A blued weapon is not immune to further rusting, but it is a huge improvement over browning or simple oil coats. Most competent gunsmiths will will be able to blue.

Parkerizing
Large-scale conflicts saw the expedited production of weapons and the need to make them as durable as possible. The early1900s became the era of Parkerizing, which is a method of phosphating that gun owners still utilize today.

Parkerizing, a name that comes from the Parker Company that popularized it, is an extremely durable, wear-resistant, and nearly corrosion-proof finish that turns metal a dark grey. This finish saw extensive use in the United States during World War II. Readers may recognize this as the surface treatment used on the M1 Garand and 1903A3 Springfield, among others. Many people use Parkerizing today on hard-use guns, often as an underlayer to which modern ceramic coatings can be applied.

This finish carried over into the Vietnam War, where it was used on the M14 and M16. The M16, making its war debut, had most of its parts made from aluminum and new steel alloys, and wasn’t at all prepared for the dense, wet jungles of Vietnam. The rifles literally rotted away in the hands of those trying to fight with them. To make matters worse, the enemy had the AK-47, a superior weapon in nearly every category. How was it that a space-age society delivered a gun to the battlefield that was so inferior?

The answer comes right back to the black powder days. Soldiers in Vietnam were told the M16 didn’t need much cleaning, because it was technologically advanced. Realistically though, the M16s were made of what were basically uncoated parts and unlined barrels. The powders used early on caused the guns to foul up and attract moisture, just as was the case in the olden days of black powder. This combination led to rusted chambers, stuck cases, and too many casualties.

We’ve come a long way since those days. Today we enjoy extremely durable and advanced finishes on our metal. Most pistols that are worth anything come with PVD or Nitron finishes that will outlast the owner of the gun. Modern rifles come from the gun store with ceramic coatings and classic case-hardening.

Josh Wayner is a professional freelance journalist, nationally ranked competitive shooter, and industry consultant.

The photos in this article were taken on location at Bachelder Master Gunmakers in Grand Rapids, Michigan and feature Parker shotguns that were restored using the techniques detailed above.

Disclaimer: The views expressed in this article are those of the author and do not necessarily reflect those of Gunpowder Magazine.