AR15 BCG finishes (l-r) Black Nitride, BCM BCG with Phosphate, BCM BCG with NP3, FailZero with EXO Nickel Boron, Toolcraft with EXO Nickel Boron, Hard Chrome
There are a wide variety of finishes available for AR15 bolt carrier groups (BCGs) today and we take a look at some of the more popular ones below.
Colt BCG with matte chrome finish and nickel boron gas key
The first AR15 bolt carrier groups were hard chrome plated. This was at the direction of Eugene Stoner, the designer of the AR-15. Chrome is a finish well suited to the harsh environment where the bolt carrier group operates. It is extremely hard which makes it very wear resistant. It also has high corrosion resistance as well as a natural lubricity. Chrome BCGs are available today, but other finishes are much more common, all of which try to improve on the original chrome in either price or performance.
Bravo Company (BCM) BCG with phosphate finish
Current mil spec for bolt carrier groups in military rifles (M16 and M4) is phosphate. Some advantages of phosphate over chrome include it’s lower cost and less visible appearance in a military setting - less shiny. Properly manufactured BCGs with a phosphate finish will still have a chrome lining inside the gas key and inside the carrier where the gas rings ride. Some people like the rough phosphate finish for it’s tendency to “hold oil” better than other finishes. The roughness of the phosphate finish wears down to become a smooth surface on the high wear points like the carrier rails.
Also known as Melonite, Salt Bath Nitride or simply Nitride, this is a heat treating process that creates a case hardened surface by diffusing nitrogen into the metal surface. The resulting surface is extremely hard which makes it very resistant to wear and corrosion. Because nitrided bolt carrier groups do not require chrome lining of the gas key or inner areas of the bolt carrier, manufacturing costs are reduced. Black Nitride finished BCGs often have an attractive deep black finish.
Nickel Boron is an advanced metal finish that offers high resistance to wear and corrosion as well as having an ultra low co-efficient of friction. A nickel boron bcg will have greater lubricity and corrosion resistance than both chrome and nitride BCGs. For these reasons, it is a very popular AR BCG finish. UCT Coatings of Palm City Florida applies their patented EXO Nickel Boron finish to many products including AR-15 BCGs for Fail Zero and Toolcraft.
This Bravo Company (BCM) BCG has been refinished with NP3+ by Robar
NP3 is a proprietary finish offered by Robar Inc. It is an electroless nickel-based finish for steel, stainless steel and aluminum alloys that co-deposits sub-micron particles of PTFE (polytetrafluoroethylene), otherwise known as Teflon™, with electroless nickel. It is extremely slick while also being very corrosion resistant. It has a dull gray finish darker than chrome and nickel boron.
When it comes to finishes for AR-15 BCGs, the sky is the limit. All of the finishes listed here are quality finishes and a good BCG will work fine with any of them. What finish you select becomes pretty much a matter of personal preference. By weighing the pros and cons of each finish against your requirements and budget you will be able to make the right decision.