Building your own AR-15 or some other customized sporting platform? You can make that thing point, cycle, and shoot just how you like. While many assembled uppers will come with an upper receiver, barrel, handguard, gas block, and tube, charging handle, and some will even come with ejection port covers, forward assists, and muzzle brakes, most lack a bolt carrier group.

That’s not something to lament. It’s just a golden opportunity for you to dial in the performance of your new rifle. The BCG is like the heart of your rifle, and by hand-selecting one, you can make it tick as you please.

Here’s what you need to know.

Nickel Boron
Nickel boron coatings are applied to bolt carrier groups via a process known as electroless plating, in which a nickel boron coating is deposited on the surface of the bolt carrier group through a chemical reaction.

Bolt carrier groups with a nickel boron coating are typically shiny and silver. The process leaves the BCG with an extremely hard, very slick coating that is chemical and corrosion-resistant.

It also exhibits a trait known as permanent dry lubricity. Typically, the moving parts in a firearm must be treated with a liquid lubricant such as gun oil, in order to minimize friction. However, oil must be applied periodically and when too much is applied, it serves as a magnet for dust, sand, grit, and dirt, which can all abrade the components of a firearm.

The slick coating of the nickel boron, however, has “dry” lubricity. That is, it is “slick” and needs a minimum of oil to keep friction down. This also makes them easier to clean, which is an added bonus. They can often simply be wiped down.

Black Nitride
A black nitride coating is applied to the surface of a bolt carrier group through a heat treatment that allows nitrogen to diffuse across the surface of the BCG. In contrast to nickel boron coatings, which tend to leave the BCG silver or golden, a black nitride coating is black and slightly lustrous.

Black nitride finishes are relatively popular because they are also relatively affordable, especially when compared against nickel boron finishes which tend to be more expensive. However, black nitride BCGs also offer a number of benefits.

Like nickel boron coatings, black nitride coatings are extremely hard, extremely resistant to damage, and also chemical and corrosion-resistant. Also like nickel boron coatings, black nitride coatings exhibit a high degree of permanent dry lubricity.

This diminishes their reliance on liquid lubricant, helping to prevent the overuse of oil that can trap dirt, dust, and other damaging debris. Since they require less liquid lubricant, many users also consider them easier to clean.

Other BCG Options to Pair with an Assembled Upper
These are not, however, your only two options when it comes to pairing a BCG with an assembled upper. You can also choose:

– Phosphate: Affordable, mil-spec, tough, corrosion-resistant, but harder to clean and not the highest level of permanent dry lubricity.

– Hard Chrome: Common, tough, corrosion-resistant, but relatively expensive.

– Titanium Nitride: Titanium nitride coatings on BCGs are expensive, but they offer excellent permanent dry lubricity and corrosion resistance.

Check out MCS Gearup
Looking for a new BCG to pair with your 5.56 NATO upper receiver, for a complete upper receiver assembly, or an AR-15 upper or lower parts kit? Check out MCS Gearup to pick up the parts you need and reach out to their customer service team if you have any questions about products, parts, or processes.

You can reach them at 239-848-6757 or at with questions.

For more information about M Lok Rail System and Lower Parts Kit GLOCK 43 Please visit: MCS Gearup.