Gun Coatings And Treatments

BY Herschel Smith
1 month ago

Shooting Illustrated:

Plated
Reflective, plated finishes such as hard chrome, nickel and gold have been around longer than anyone presently reading this magazine. While no longer popular on long gun exteriors, surface treatments like chrome-plating work well on and in certain internal components. Most tactical-rifle shooters have experience with chrome-lined bores, which provide wear- and corrosion-resistance. We also find chrome in less-obvious places like piston-rod ends, the inside of an AR’s bolt carrier and in the open end of the carrier’s gas key. One complication to chrome-plating is that it adds to the dimensions of finished parts, so components must be undersize by whatever thickness the plating will add.

Attempts to chrome-line rifle bores date back to the first half of the 20th century. The process has long since become standard in military and police battle rifles and carbines around the world. Sources for true match-quality, chrome-lined barrels can be counted on one hand, with fingers left over. Most chromed bores are very durable, but they typically come up short in the accuracy department due to variations in thickness throughout the bore. Chrome-plated parts are slicker than bare steel, allowing for easier cleanup of pistons and bolt components. Unfortunately, the constant slamming of metal on metal can cause chrome to wear or flake off of hard-use parts like bolt-locking lugs, which can affect accuracy, reliability and even safety. Chrome plating seems to do its best work inside of components subjected to high friction—but not hard impacts—and when done well, is still a great solution to limit erosion and wear.

Nickel-Boron
Nickel-boron (NiB) is an “electroless” gun coating, instead applied chemically. That makes for extremely uniform surface coatings on parts with tight tolerances, like a trigger’s sear-engagement surfaces. NiB reduces friction and speeds the cooling of high-heat components due to the increased surface area created by the coating’s texture. Internal rifle components appear to be the best-suited for NiB, and in my experience, this gun coating is much more durable than traditional plated finishes on contact surfaces like bolt-locking lugs. NiB provides excellent corrosion resistance, but over time it will give way to the ravages of high heat and pressure on hard-use components. NiB-coated components are relatively easy to clean up but may become discolored when subjected to high heat.

Nitride
Names like Melonite, Ni-Corr, Black nitride or salt bath nitride are all variations of a surface treatment formally known as “Liquid Salt Bath Ferritic Nitrocarburizing Non-Cyanide Bath” (FNC) or simply nitriding. This process isn’t really a gun coating, since it doesn’t change a part’s finished dimensions, so it is well-suited for both precision internal components and bores. An added plus is, unlike chrome lining—which is mostly limited to chrome-moly steel blends—nitriding is optimal for stainless-steel bores, too. Its high resistance to wear and corrosion also make it useful as an external surface protectant. Nitrided surfaces are very hard and, since the FNC process transforms the surface rather than coating it, the metal itself must be removed to get through to unprotected steel below. I have been using nitrided barrels, bolts and trigger groups for years and have yet to wear one out. From a production standpoint, nitriding is inexpensive and so long as it is done correctly, the high temperatures that the process relies on for application will not harm steel rifle components.

Spray-on
Gun coatings such as Cerakote, DuraCoat and KG Gunkote are applied via compressed-air sprayers. They differ somewhat in composition and may be air- or heat-cured. Spray-on coatings are best-suited for rifle exteriors where the inevitable variations in thickness will not change tolerances nor impede function. They have a fair amount of wear resistance, but heavy use or careless handling can still cause them to wear through, scratch or chip off. When properly applied, spray-on gun coating provides good corrosion resistance and allow you to truly customize your rifle’s appearance due to endless color and pattern variations. Spray-ons have the added benefit of being equally well-suited for aluminum, polymer and wooden rifle components, too. These finishes are susceptible to harsh chemical strippers like acetone or ammonia-based solvents, so stick to safer cleaners like mineral spirits or conventional powder solvents when cleaning painted rifles.

I’ve always thought I needed to know a little more than I do about both the materials and the coatings for firearms.  Unfortunately, I only took one materials engineering course in school, and most of the time materials engineering is left to the folks who do it all the time.

But this article is a good start on coatings.  I welcome reader feedback if you find any other articles or papers on the subject, or just want to weigh in with your own expertise.


Comments

  1. On May 19, 2019 at 10:58 pm, MTHead said:

    POF-USA uses NIB coating on their bolts. Our P416 machinegun was over 16,000 rnds and it had smoothed out in hard wear spots. but hadn’t worn off at all. it’s “dry lube” properties make it desirable for suppressed weapons that carbon up fast. and its just another example of aftermarket innovation pushing reliability. Worth the money.

  2. On May 20, 2019 at 6:04 am, ragman said:

    I’ve had good luck with a Brownells spray on epoxy named Aluma Hyde II. It appears to be very durable, comes in many colors and does not require heating in an oven. However, it takes about a week to dry completely and you can’t rush the process.

  3. On May 20, 2019 at 2:37 pm, Fred said:

    I’ve had one rifle done in Cerakote. Excellent results. I trusted the guy more than the type of coating and was not disappointed. The color is so cool. I love it for that reason alone but, oh yes, you got it snappy mac happy, the gun goes BANG. Every. Single. Time.

  4. On May 20, 2019 at 8:24 pm, Donk said:

    Maybe off topic but due to the recent red flag laws I have started to disperse my collection. I invested in storage bags and bore tubes a la https://www.zerustproducts.com/. New product for me and all stored weapons/electronics are in humid environments (curse of the south in summer). The stuff is in the zippered bags and in either a strongbox or Pelican cases. 5 year life on the vapor emission technology, I will check every month and perhaps report back. I don’t blog or FB or IG or twit or any other social media, only here and WRSA.

  5. On May 20, 2019 at 8:44 pm, Gryphon said:

    Donk – the Best and Safest Protective Method for Firearms is a Heavy Coating of Mil-Spec Corrosion Preventative Compound, either MIL-C-16173D or subsequent Materials. This is “Cosmoline” (an old Trade Name) and LPS-3 is a modern equivalent. Newer compounds are ACF-50 and Corrosion-X, both are the current standard used in Aviation for protecting Bare Metals. “Lubricants” like Break-Free or WD-40 and other ‘gun oil’ products have only Limited Effective Life as Preservative Materials. True Corrosion Preventatives Don’t Evaporate, or have much Volatile Solvents.

    As for those “moisture barrier bags”, unless you put a Desiccant (Moisture Absorbent) in with the Item, that Humid Southern Air that is already in the Bag or Container is Locked In with the Item. Same thing applies for Pelican Cases, Ammo Cans, and PVC Pipes…

  6. On May 20, 2019 at 9:16 pm, Donk said:

    @Gryphon Thanks for tip. I know Cosmoline all too well (was a Millwright then Engineer in a shipyard in the South for 20 years responsible for weapons systems (CIWS, NATO Seasparrow, ALRE equipment, etc.). A bit** to remove, especially if it is an old application. I used me vacuum sealer and put a healthy portion of desiccant beads in all the bags – have several #10 cans of them. The Pelican cases are just to add another “vapor barrier.” Like I said, it’s a new protocol for me and I will be checking regularly and perhaps report back. My primary concern are my Trijicon MROs and SWFA illuminated reticle scopes.

    Mil surplus ammo cans, I can speak directly to them as a “vapor barrier” having cached ammo and bare FE parts for test with desiccant for several years. They work – underwater even.

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This article is filed under the category(s) Firearms,Guns and was published May 19th, 2019 by Herschel Smith.

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