General

The Skinny on Nitride Barrels

After I wrote about the Faxon barrel I’m using in the latest project, a question arose about the benefit of nitrided barrels. I’m not surprised, since the gold standard for so long has been chrome lining. Nitriding is just the “new thing” that all the cool kids on the internet are talking about.

But, what is it? Does it have any benefits over the tried and true methods? I want to dig into that for a bit.

Here is a quick description of the process from an industrial coating company, IBC Coatings, I’ve bolded some key elements.

Salt Bath Nitriding/Nitrocarburizing was originally created as an alternative to gas nitriding that would produce a more uniform case through surface contact between the substrate and liquid salt. When steel parts are placed into a preheated liquid salt, there is sufficient energy localized near the surface due to differences in chemical potential that then allows nitrogen and carbon species to diffuse from the salt into the steel substrate. The process is carried out at 750-1050°F, making it faster than gas nitriding. Lower temperature cycles produce an S-Phase/Expanded Austenite case in stainless steels. Post-oxidation after nitriding combined with polishing produces coatings with exceptional appearance (black color) and high corrosion resistance (greater than electrolytic chrome plating). To ensure part quality, our salt baths are continuously monitored, with chemistry adjustments made when necessary.

Salt Bath Nitriding/Nitrocarburizing is well known under various trade names, including ARCOR®, TENIFER®, TUFFTRIDE®, MELONITE®, and QPQ®.

The idea here is that the barrel is immersed in a sodium-nitrogen solution and heated to a high temperature. The ensuing chemical reaction causes the nitrogen to diffuse into the surface of the barrel (inside and out) and convert a thin layer of the surface into a very salt-bath-nitriding-dhn.gifhard coating. From what I can find, the surface of a nitrided barrel is in the realm of 60 to 65 Rockwell, while the typically gun barrel steel is 28-32 Rockwell. This surface layer becomes a very corrosion resistant “case” around the barrel steel.

Additionally, the surface layer created by the nitriding process has a much lower coefficient of friction compared to bare metal or chrome. Ostensibly, this would mean that nitriding barrels may present a small boost in velocity. I have read some accounts verifying this on Accurate Shooter, but it was only by about 1% or so. Still, a boost is a boost and nobody will ever turn down velocity.

 

The real benefits of this process is that nitriding performs all the same functions as chrome, such as increasing corrosion resistance and prolonging the life of the barrel, and it does it without the associated negative impacts on accuracy. Since the surface of the bore is being converted into a harder material, rather than adding a new layer of material, the uniformity of the bore is maintained. As I’ve mentioned before, consistency is accuracy.

From my reading, this process is not perfect, though. The surface may be harder than chrome, but it is not as heat resistant. Weapons fired on fully automatic for prolonged periods may burn through the nitrided layer quicker than a comparable chrome layer. This should not really be a factor for semiautomatic weapons, though. Also, per the bolded portion in the paragraph above, the barrel must be heated to a temperature of 750 to 1050 degrees fahrenheit. Coincidentally, this is about the same temperature that barrels are heat treated/stress relieved. There is a very real risk that heating to such temperatures (particularly with stainless barrels) can undo heat treatments already performed by the factory that machined the barrel to begin with. While I haven’t seen anyone mentioning decreases in accuracy after nitriding, I have seen many warnings to not perform the process on a barrel that’s already been fired a significant amount. The micro cracks in the surface of the bore and chamber of such barrels may be aggravated by the high temperatures, making them worse and degrading accuracy.

The Faxon barrel I purchased is my first real experience with a nitrided barrel. I’ve handled at shot some rifles with them before, but I’ve never done accuracy evaluations or had to care for one. For the most part, I’m told that care procedures are the same- except that some products (like those from Bullfrog) will tend to discolor the finish.

I will continue reporting back on my results. If you are waffling back and forth on a standard barrel or chrome lined barrel, I don’t think you can really go wrong either way as long as the barrel is well made. Find one that suits your needs in size, profile, and accuracy and let the manufacturer worry about the rest.

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2 thoughts on “The Skinny on Nitride Barrels”

  1. What’s interesting is that it is well known that moly coated bullets (which have a lower level of friction than copper bullets) reduce the Velocity of the loading.

    This is in part related to the reduction in pressure required to accelerate the bullet down the barrel. The copper bullet acts as a stronger cork allowing the powder to reach higher pressure as it accelerates the bullet down the barrel.

    So friction (to a point) in the system should increase pressure and thus velocity while lowering friction should have a opposite effect.

    So whatever melonite is doing to increase velocity that your sources are noteing may be attributed to something else, but what?

    1. What you write makes a lot of sense. My own searching seems to turn up about 50/50 with one side saying there is a velocity decrease due to reduced friction, and the half saying velocity increase.

      Perhaps the velocity increase has less to do with the nitriding itself, and more to do with other factors such as changes to barrel dimensions.

      I have been wondering the same thing about polygonal/ratchet rifling. If the rifling pattern has less “grip” and reduces friction, how is it that folks are seeing higher velocities?

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