There’s far more to bolt carrier groups than standard mil-spec phosphate finishes. Some bolt carrier groups are treated with advanced finishing and coatings that offer a wide range of different benefits. Here are some of the more common among them.
Hard Chrome
Eugene Stoner, the person who actually designed the AR-15 rifle, ordered that the first models be made with hard chrome coatings. This is a basic coating that nonetheless is appreciated for its permanent dry lubricity, which means it requires less liquid lubrication to operate smoothly.
Relatively rare today, hard chrome bolt carrier groups are very wear and corrosion resistant. One note is that the extractor should preferably be phosphate coated because chrome’s lubricity is too high to effectively and reliably engage the casing.
Phosphate
Mil-spec bolt carrier groups are phosphate coated, which are popular primarily because of their low cost of production as well as their low reflectivity, which helps keep the rifle and the person carrying it discreetly situated.
However, phosphate has a relatively low permanent dry lubricity, which means two things. While it holds on to liquid lubricant more effectively, the catch-22 is that it needs more of it to operate smoothly without overheating.
The rougher finish of phosphate-coated AR15 BCGs also means that cleaning is a bit more difficult as the tooth of the finish “holds onto” fouling and other debris.
Black Nitride
Black nitride is also known as melonite, as well as simply and generically as “nitride”. Black nitride is a finish that is electrochemically applied to the AR15 BCG; it is a case hardening process that diffuses nitrogen onto the surface of the bolt carrier group, converting it chemically.
As a result, black nitride bolt carrier groups have an extremely hard finish that, though thin, is very wear and abrasion resistant. It also happens to be the case that black nitride has a very high degree of permanent dry lubricity, which means that it needs less liquid lubrication to run smoothly.
As a result, it does not hold onto fouling or attract it as readily, which also means that it is easier to clean a nitrided bolt carrier group.
Titanium Nitride
Titanium nitride is an advanced ceramic coating, one that like black nitride offers an excellent degree of dry lubricity as well as high hardness, which gives it excellent wear resistance. It also offers a very high degree of corrosion resistance.
Like black nitride, its high permanent dry lubricity means that less liquid lubrication can be used with it, as well as that it is easier to clean because it will not cleave to fouling.
Another big benefit of titanium nitride is its uniqueness. Many shooters choose titanium nitride AR15 BCGs because of the unique gold-tone looks it sports.
The downside of titanium nitride bolt carrier groups is that they are fairly expensive.
Nickel Boron
Nickel boron is a unique and advanced AR15 BCG coating that, like nitriding, offers a very low degree of friction thanks to its high permanent dry lubricity.
This means that like nitrided bolt carrier groups, those that sport a nickel boron finish will require less liquid lubrication and will also be easier to keep clean. Nickel boron is also very hard and very corrosion resistant. The drawback is that it is one of the more expensive bolt carrier group finishes.
Diamond-Like Carbon (DLC)
Diamond-like carbon, more commonly known simply as DLC, is an advanced coating that is applied in a process known as PVD, or physical vapor deposition, that deposits a thin layer of extremely hard carbon on the surface of the bolt carrier group.
An AR15 BCG with a DLC coating will be very hard, which confers a high degree of wear resistance; it will also be highly corrosion resistant and offer excellent permanent dry lubricity.
As a result, less liquid lubricant can be used with a bolt carrier group that has a DLC coating, and it will be easier to keep it clean as well.
However, as with some of the other advanced finishes and coatings mentioned here, DLC coatings can be prohibitively expensive.
Why a Bolt Carrier Group with a Modern Finish?
Some of the modern coatings and finishes mentioned here that are commonly applied to AR15 bolt carrier groups offer some significant and substantial benefits. Here are the common ones:
- Permanent dry lubricity that requires less liquid lubrication.
- The same trait also makes it easier to keep the bolt carrier group clean.
- Higher lubricity results in smoother, faster cycling.
- In the case of some, such as titanium nitride and hard chrome, the BCGs offer aesthetic uniqueness and appeal.
- These coatings are hard, wear-resistant and corrosion-resistant.
All in all, if you’re looking to boost performance beyond the basics of a phosphate-coated BCG, some of the coatings and finishes mentioned here may represent solid options.
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