AR 15 Parts Kits: About BCG Coatings

There comes a time in the life of everyone building an AR-15 rifle (or some other similar black rifle) that he or she must decide on what sort of BCG coating to use.

The BCG, or bolt carrier group, is, as you may know, the component that contains the firing pin and gas rings, and which feeds, fires, extracts, and cycles the action. In many ways, it is the heart of the rifle, without which the entire platform would not operate.

It was not too long ago that the market was only prepared with a few different options, but modern BCG coatings have taken permanent dry lubricity and corrosion resistance to the absolute max.

Choosing a high-quality BCG for your AR-15 build, one that features better dry lubricity and corrosion resistance can improve cycling times and diminish wear and tear on a rifle. Let’s take a look at why this matters so you can apply this knowledge as you pore through collections of AR-15 lower parts kits and assembled uppers.

Phosphate Coatings

Phosphate coatings are the standard when it comes to AR-15 and M16 rifles, and if you see a BCG listed as “mil-spec” then it has a phosphate coating.

Phosphate coatings are black and have a bit of tooth to them that is not quite rough; more like a matte surface.

Some users prefer these coatings because the “toothiness” of the BCG surfaces holds oil better than other coatings. At the same time, these finishes wear more easily and require more oil to lubricate them, so holding oil better while needing more may be a bit circular.

Phosphate coatings are also non-reflective and more affordable, both of which are attractive to some tinkerers. However, despite the more attractive price point, cleaning a phosphate-coated BCG is a bit more labor-intensive.

Hard Chrome

Hard chrome bolt carrier groups were actually the first ever devised for the AR-15 by Eugene Stoner.

Today, while hard-chrome BCG coatings are slightly more expensive than some others, they are still appreciated by some for their good corrosion resistance and the fact that they have superior permanent dry lubricity when compared to phosphate coatings.

They’re not common and they are reflective, but they are easy to clean and are the “traditionalist” option, so some shooters prefer them.

Black Nitride

Black nitride, also known simply as nitride, might appear to the unpracticed eye at first glance as a phosphate coating, but black nitride is much harder, more durable, and reflective.

Black nitride is a heat treatment process that diffuses nitrogen onto a thin layer at the top of the BCG’s steel surface.

The resulting finish is very hard and chemically resistant, which makes black nitrided BCGs resistant not only to wear but also to corrosion. They also have a very slick surface which offers excellent permanent dry lubricity.

The downside is that they are more expensive than phosphate coatings.

Nickel Boron

Nickel boron results in a bright, chrome-like finish that has a similar appearance to that of hard chrome bolt carrier groups. However, nickel boron BCGs have an extremely slick surface and a lower coefficient of friction than both hard chrome and black nitride bolt carrier groups.

Though they are slick, chemically resistant, easy to clean, and durable, they are more expensive than many other finishes.

Nickel Teflon

Nickel Teflon coatings look a bit like nickel boron and have a pretty slick silvery appearance. However, they have an even lower coefficient of friction than nickel boron, and like it, are extremely slick and tough.

The Teflon coating, in addition to having an excellent permanent dry lubricity rating, is also non-wetting and non-stick and can repel water, oil, and grease, keeping the surface of the BCG clean.

Titanium Nitride

Titanium nitride is a ceramic coating that offers many of the benefits of the other BCG coatings listed here, being hardness, permanent dry-lubricity, and corrosion and wear resistance. This makes it similar in performance to BCG coatings like black nitride and nickel boron.

What titanium nitride offers which the others don’t, however, is a slick, somewhat golden appearance, which is the main reason for its popularity.

Diamond-Like Carbon

Finally, we have diamond-like carbon coatings, which are also referred to as DLC coatings. Diamond-like carbon is applied through a process known as PVD, or physical vapor deposition, in which a layer of carbon is vaporized and applied to the surface of the bolt carrier group.

DLC coatings are extremely hard, corrosion and wear-resistant, and like the other finishes here, very slick, which gives them low coefficients of friction and superior dry lubricity.

Extremely hard, nearly scratch proof and all but corrosion resistant, DLC coatings are both practical and attractive; however they are difficult to apply and therefore fairly expensive.

Why Permanent Dry Lubricity Matters (in Terms of an AR 15 Parts Kit)

Aesthetics aside, you may have noticed that a common trope here has to do with permanent dry lubricity - that is, how slippery a coating is without the help of a liquid lubricant like gun oil.

The better the dry lubricity of a material, the less wear it will experience in its bearings and in contact with moving parts. Consequently, BCGs with better permanent dry lubricity both last longer and wear less on the parts they contact. They also cycle more rapidly, which in turn can mitigate recoil and boost platform rate-of-fire.

Moreover, the better the permanent dry lubricity of a platform, the less it will need to rely on supplemental liquid lubricant. Gun oil, though it cuts friction, also serves as a viscous magnet for dust and dirt which in turn, ironically, accelerate wear on gun parts.

So, all in all, bolt carrier groups with permanent dry lubricity wear less, last longer, are better for the rifle, and are easier to wipe clean.

Need an AR 15 Parts Kit?

Whether you’re looking for an AR15 lower parts kit that comes with a buffer tube and a pistol grip or a complete build kit with an assembled upper and a BCG included, the parts you use to complete your AR matter, down to the bolt carrier group’s finish.

Look through our collection of AR 15 parts kits and if you have any questions about what you need to complete the build feel free to contact us.