Choosing The Best Bolt Carrier Group

Posted by Modulus Arms on 3rd Feb 2023

Choosing The Best Bolt Carrier Group

The AR15 bolt carrier group (BCG) is one of the most important parts of the gun. In one smooth cycle, the AR15 BCG chambers the round, cycles the gun to eject the spent casing, chambers another and resets the gun’s hammer. The mass of the AR15 BCG is what helps cycle the gun with the buffer assembly. Simply put - without the AR15 bolt carrier group, bang stick no go bang. Because of this, it’s imperative to choose the best bolt carrier group. Not certain where to start? Well, grab some red Kool-Aid and let us here at Modulus Arms help you out.

What is an AR15 Bolt Carrier Group (BCG)?AR15 BCG Diagram

PC: The Truth About Guns

We’ve gone into what an AR15 BCG does above, but to get more specific for a minute, the AR 15 BCG contains (mainly) the following major parts:

  • Bolt Carrier - this is the main body that holds all the parts
  • Gas Key - Tube attached to the carrier that catches gas from the gas tube
  • Bolt Carrier Key - connects from the bolt carrier to the gas tube and directs gas into the carrier
  • Bolt assembly - part at the end of the AR 15 BCG that holds the ejector, extractor and gas rings. This guises the firing pin and extracts/ejects the empty casing after firing
  • Bolt Cam Pin - Guides the bolt forward and backwards
  • Firing Pin - The part that hits the cartridge primer
  • Firing Pin Retaining Pin - Hold the firing pin in place via the hold on the side of the AR15 BCG

Full-Auto vs. Semi-Auto Bolt Carrier Groups

Difference between full auto and semi BCG's

Full-Auto Vs. Semi-Auto AR15 Bolt Carrier Group Comparison. Spot the difference! PC: Gunmann

A full auto BCG vs. a Semi auto BCG might seem like the potential for massive differences but in reality, they are very similar. A full auto AR 15 BCG simply has a larger lug that allows the gun to fire automatically when the lug is in contact with the sear release in a full-auto trigger assembly.

While a full-auto AR15 BCG is not illegal unless paired with the aforementioned parts, it’s important to mention that it’ll be a good bit heavier than the semi-auto AAR15 BCG, so unless we’ve got some deep pockets to afford a legal Class 3 machine gun, there isn’t much point to purchasing one overall, but it is important to mention that many (if not most) AR15 BCG are already full-auto to begin with, but due to the lack of auto-sear, etc, they are not going to be fully automatic.

Coatings for BCGs

Let’s be clear right off the bat, some AR15 Bolt carrier group coatings are truly nothing but marketing. That’s not to say all of them are snake oil by any means - some are fantastic, but some are absolutely not providing any benefits. Coatings can help a lot when it comes to performance of the AR15 BCG. Let’s take a look at some of the more popular AR 15 BCG coatings.

Phosphate (parkerized)

Parkerized AR15 bolt carrier group options have been around since the very (essentially) beginning of the platform. Mil-spec guns usually have their BCGs parkerized and it’s the most common coating for civilian ARs as well. Phosphate holds up very will with millions of combat guns across the globe and while being more inexpensive, is an excellent choice.


Black Nitride is another popular AR 15 BCG coating, and is a derivative of Nickel Boron. Black Nitriding increases the hardness of the metal without adding a thick coat. Black Nitride is a great choice for an AR15 BCG because it is very durable and highly wear-resistant. Side note: Black Nitride won’t flake off either and is very easy to clean.


Chrome was originally available on some of the early AR/M16s in the U.S. Military, but that coating quickly moved to Phosphate. While this CAN be a durable coating for an AR15 bolt carrier group, it’s also prone to flaking due to the chrome plating process. Try to skip a chrome AR 15 BCG if it’s an option, and these days? It certainly will be an option.

Diamond-like carbon (DLC)

Diamond-like Carbon is an excellent choice for an AR15 bolt carrier group. A mix of graphite and “diamond-forms of carbon”, the coating forms a molecular bond coating as hard as? You guessed it - diamonds. Because of this, DLC makes an excellent, easy-to-clean, durable coating for an AR 15 BCG.

Recommendations for the Best Bolt Carrier Groups

There are many great AR 15 Bolt carrier groups on the market right now, but here are a few of our favorites. When putting this list together we considered a few factors:

  • Durability
  • Speed
  • Quality
  • Price

Again, these are just a few of our favorites and by no means is it an exhaustive list, we’re just hoping to give a few great options! Let’s check them out!

Bravo Company Manufacturing (BCM) M16 BCG



A very fairly-priced AR15 BCG comes from a very well-respected manufacturer in the BCM M16. Machined to USGI specs and with a parkerized exterior/chrome lined interior, the BCM BCG is an excellent, Mil-Spec choice that will hold up very well for years. 

Geissele Enhanced Reliability AR15 BCG

Geissele BCG

Geissele Enhanced Reliability AR 15 Bolt Carrier Group. PC: Midway USA

Geissele are well-known for some of the best AR15 parts and rifles in the business, so it should surprise no one that their AR 15 BCG is making this list. For a step above basic Mil-Spec, the Geiselle BCG is made of hardened 158+ Carpenter Steel that was refined specifically for Geissele. The Bolt is forged and then Geiselle applies a specialized chrome-nitride finish called “Nanoweapon” to the bolt, which allows it to function faster, slicker and with less lubricant. All this goodness come at a price though, expect to pay over $350 for this  AR 15 BCG from Geissele.

Daniel Defense AR15 BCG

Daniel Defense AR15 BCG

Daniel Defense AR15 Bolt Carrier Group. PC: Daniel Defense

In the world of pro user Ar15’s it is hard to find companies with as much pedigree as Daniel Defense. The Daniel Defense AR15 BCG is an excellent option that is machined from 8620 steel, heavy phosphate coated with chrome lining and put through a battery of pressure tests and inspections. This AR15 BCG from Daniel Defense comes in under $250 - making it a solid deal for the price and performance.

Rainier Arms Match Grade Nitride AR 15 BCG

Rainier Arms AR15 BCG

Rainier Arms Nitride Precision Match Grand AR15 BCG. PC: Rainier Arms

Rainier Arms are another company that are well-known for AR15 parts and accessories - as well as high end complete rifles. The Rainier Arms Precision Match Grade AR15 BCG is finished in Nitride over SAE 8620 Steel and is engineered to meet or exceed Mil-Spec requirements. At a comfortable price in the middle, the Rainier Arms Nitride Precision Match Grade AR15 BCG is definitely worth a look at only $169.95.

Palmetto State Armory Full Auto AR 15 Bolt Carrier Group

PSA AR15 Full Auto BCG

PSA AR15 Bolt Carrier Group. PC: Palmetto State Armory

If budget is a serious concern the PSA AR15 BCG is an excellent choice. PSA are known for producing affordable weapons systems and parts and this AR 15 BCG comes high pressure tested, made from bar stock steel and is phosphate coated. This AR15 BCG from PSA comes in right around $70.

Faxon Firearms M16 AR15 Bolt Carrier Group

Faxon Firearms BCG

Faxon Firearms M16 AR15 Bolt Carrier Group. PC: Wing Tactical 

Faxon are known not only for rifles and handguns, but also for some of the best aftermarket AR15 barrels in the business. The Faxon AR15 BCG is described as “better than Mil Spec”, all components are nitride coated, highly tested and heat-treated for reliability for years to come. This AR15 BCG comes in right around $140-190 - depending on the options and finishes selected.

Final Thoughts

We hope this helped start you on the path to finding the right AR15 bolt carrier group. While it might seem like the differences are subtle in this part category… You’re right. The reality is that this can be a topic that makes most folks' eyes glaze over as it’s not very exciting at all. However, the AR15 BCG is one of the most important parts to take into consideration when building an AR15.