​What is the Best Bolt Carrier Group | Best AR 15 BCG

​What is the Best Bolt Carrier Group | Best AR 15 BCG

What is a Bolt Carrier Group and its Purpose?

A bolt carrier group (BCG) is the removable part of your rifle that contains the operating parts of your firing mechanism. Simply put, it's the "group" that operates the firing pin, the extractor, the ejector, and all other parts of your firing system. The extractor rod is one of the most important parts of your firing system. The extractor rod is also known as the "ejector rod". It is one of the three main rods in your firing mechanism. The other two are the "striker" rod which cocks the firing pin and the "return" rod which returns the bolt to the ready-to-fire position.

Black Nitride BCG | Best AR 15 BCGs

Full Auto vs Semi-Auto Bolt Carrier Groups

A BCG that is described as a “full-auto” BCG is a little misleading to the beginner who has little to no understanding of the way an AR 15 actually functions. Let's start off by reassuring you that they are legal and unlike the name suggests do not make your AR 15 automatic firing.

The BCG is slightly longer and heavier. The full-auto bolt carrier group has a recognizable additional lug at the rear of the bolt carrier group. This rear lug pushes the sear release downwards which allows full auto (or burst) fire in a rifle that contains all other components necessary for that. However, in a standard semi-automatic rifle, this has zero effect on how the gun functions.

Semi-auto bolt carriers have become the ugly stepchild of the BCG world and don’t maintain much of a real purpose. Any builder wanting to build a mil-spec weapon would avoid it as they would require commercial buffer tubes and stocks.

Semi-auto BCGs are lighter and thus less reliable. They contain less overall mass, which many believe is necessary for proper reliable function. The cost savings that was once a small reason for consideration is no longer present.

For this reason, we suggest just purchasing a mil-spec full-auto version.

The 3 types of BCG's

This is really just a different way of saying the same thing as above. But let's take a little different approach as we define the three types.

AR 15 Style BCG

  • The semi-automatic bolt carrier group
  • Lighter weight than a full-auto bolt carrier group
  • Typically made to be Mil-spec
  • Cycles faster due to less mass
  • Does not require an adjustable gas system

M-16 Style BCG

  • The full-automatic bolt carrier group
  • Heavier weight than other carrier groups
  • Made Mil-Spec
  • Cycles slower than lightweight BCGs for more accuracy
  • Does not require an adjustable gas system

Lightweight/Low Mass BCG

  • The semi-automatic bolt carrier group
  • Very lightweight for easier maneuverability
  • Used by 3-gunners
  • Cycles fastest for increased rate of fire
  • Requires an adjustable gas system

The Different BCG Coatings


There are many different coatings for BCGs. They all have their benefits and drawbacks. So the key is to decide what you need, want and can afford. For the most in-depth dive into the different coatings for BCGs read this "BCG COATINGS EXPLAINED" from the Learning Center from Black Rifle Depot.

Nickel Boron

Has a very shiny (silver), smooth, self-lubricating, finish that is easy to clean.

Black Nitride/Melonite

Has a very shiny (black), smooth, non-self-lubricating, finish that is easy to wipe clean.


Has a matte black finish, is hardened, non-self-lubricating, and requires a more rigorous cleaning.

Nickel Teflon

Has a very shiny (silver), smooth, self-lubricating, finish that is easy to clean.

Titanium Nitride

Has a very shiny (gold), smooth, self-lubricating, finish that is easy to keep clean.


Has hard chrome plating, that is shiny (silver), smooth, and wipes clean.


Comes in any color combination you can create, is smooth, provides protection, and helps make cleaning easy.


The only coating or treatment that is scratch-resistant, it's a matte black finish and requires rigorous cleaning.

Should You Replace or Upgrade Your BCG?

As a parts retailer, I would love to say "yes, you should replace and upgrade your BCG every year." But as an avid AR owner, builder, and frequent shooter, I feel obligated to say "not necessarily." You need to ask yourself a few of these frequently asked questions first.


Q: Is your current BCG having any operational issues?

A: If so, get a new one.

Q: Is your BCG at minimum Mil-spec?

A: If so, you're probably good to go.

Q: Are you wanting a different look or aesthetic?

A: If so, check out the Nickel Boron or Titanium Nitride.

Q: Do you just want to have an easier time cleaning?

A: Grab yourself a Black Nitride treated BCG.

The truth is, standard mil-spec parts are all they need to be, reliable. But if you want to bling up your build a little bit, get a shiny new BCG. Thanks for reading.

Shop Happy, Shoot happy, with BRD.

Aug 25th 2021 Black Rifle Depot

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