The bolt carrier group (BCG) is the heart of the AR-15 action. An AR-15 without a BCG is equivalent to a car without an engine. The BCG contains parts critical to the rifle’s primary function.
Like virtually every other part on the AR-15, you can replace the bolt carrier group and upgrade it.
Many AR-15 owners suggest buying a second BCG, either as a direct upgrade or as a spare if something on your current one breaks.
Best .300 Blackout BCG
1. Griffin Armament Enhanced Mil-Spec Bolt Carrier Group
The Griffin Armament Enhanced Mil-Spec Bolt Carrier Group answers the need for a high-quality, no-frills, mil-spec BCG.
This item is reasonably priced and is suitable for all uses. You can use it as the primary BCG for a new build, an upgrade for your existing firearm, or as a backup if your previous BCG breaks or malfunctions.
None of the parts in this bolt carrier group uses castings. Griffin Armament exclusively uses billet machined steel or steel alloy parts, all properly heat treated. The carrier is 8620 steel, the bolt is 9130 steel, and the cam pins and extractor are 4340 alloy steel.
9310 steel is an industry-recognized substitute for the mil-spec Carpenter 158 steel typically used to manufacture M16 and M4 bolt carrier groups.
The Melonite QPQ finish is also more durable than the mil-spec phosphate treatment, enhancing the BCG’s service life and giving it an attractive, deep black appearance.
This BCG also includes an extra-durable extractor spring design, rated to survive 15,000 rounds before the manufacturer recommends replacement.
2. Faxon Firearms Gunner Light Weight 5.56/.300 BLK Bolt Carrier Group
Faxon Firearms is a well-known name in the firearms industry, responsible for creating many innovative and high-quality products, most notably the ARAK-21 rifle.
The Gunner Light Weight Bolt Carrier Group is a unique BCG for 5.56mm and .300 Blackout AR-15s, oriented towards lightweight or competition builds.
All parts are fully heat-treated, shot-peened, and subjected to Magnetic Particle Inspection (MPI).
This BCG features a visually-striking gold-colored titanium nitride (TiN) finish, improving the lubricity and overall durability, protecting the BCG against corrosion, and making it easier to clean and maintain.
Each part of this bolt carrier group features high-durability steel materials: a 9310 tool steel bolt, S7 tool steel extractor, 8620 steel carrier, and 4140 steel gas key and cam pin.
The gas key screws are properly staked as well, requiring no adjustment from the user and reducing the risk of loosening.
The complete assembly weighs only 8.5 ounces, making it over 25% lighter than a standard mil-spec bolt carrier group. If you’re looking to save weight on your AR-15 built, this is the one to get.
3. Lantac Enhanced Full Auto Style Bolt Carrier Group w/ NiB Coating
Lantac USA has been manufacturing Glock and AR-15 parts since 2013 and is responsible for introducing numerous innovative products on the market, such as the BMD2 muzzle brake or the ECT1 combat trigger.
This product is part of the Lantac E-BCG line of bolt carrier groups, fully redesigned to offer higher performance and durability in every aspect while still being compatible with any mil-spec AR-15 build.
Every element of this bolt carrier group is precision machined, using 8620 steel in all parts except the bolt, made of Carpenter 158 (C158) steel.
Each part of this BCG is Electroless Nickel-Boron (NiB) finished and coated with UCT EXO, significantly improving the hardness, abrasion resistance, and lubricity of the entire assembly.
With a surface hardness ranging between 82 and 95 Rockwell C, and a friction coefficient of 0.02, this BCG is one of the most durable and easiest to clean on the market.
This BCG also possesses specially-tuned, forward-facing gas ports, redirecting and venting gases to produce a smoother and more controllable recoil impulse, and letting your AR-15 run at lower operating temperatures, even when using a short-barreled and suppressed platform.
With an overall weight of 11.7 oz, this BCG has about the same weight as a mil-spec group, preventing your AR-15 from being needlessly weighed down.
4. Aero Precision AR15 Bolt Carrier Group
Aero Precision makes AR-15 parts that offer excellent value for money, and the standard AR-15 Bolt Carrier Group is no exception.
This BCG is as close to military specifications as you can get without compromising the build quality or reliability. All parts are manufactured using 8620 tool steel, except the bolt, made instead of 9310 tool steel, a recognized alternative to Carpenter 158 in the steel and metallurgy industries.
This BCG features several enhancements over mil-spec, such as a full, inside and out NiB coating instead of the military standard phosphate treatment. The NiB coating improves hardness and lubricity, making this BCG easy to maintain and service.
For extra service life, the gas key is forged and adequately staked, and the extractor is made of tool steel, extending the number of rounds the shooter can fire before requiring maintenance. The bolt is also properly shot peened, and Magnetic Particle Inspected (MPI), ensuring high structural integrity.
5. Trybe Defense AR-15 .223/5.56/.300 AAC Complete Bolt Carrier Group
One of the best AR-15 manufacturers in the United States today is Trybe Defense. This manufacturer is not only committed to producing quality products at a reasonable price, but they are also firm defenders of the Second Amendment.
The Trybe AR-15 Complete Bolt Carrier Group is ideal for any 5.56mm or .300 Blackout AR-15 build. Although it features no manufacturer markings or stampings, this BCG is a high-quality product made of durable and long-lasting materials.
This BCG either meets or exceeds military specifications, featuring an 8620 steel carrier and a 9310 steel bolt, entirely shot-peened, Magnetic Particle Inspected (MPI), and coated with either a black nitride or a harder, more durable silver Nickel-Boron (NiB) finish.
Even with the standard nitride finish, you can expect a Rockwell hardness rating of at least 75, giving it high abrasion resistance.
This BCG functions with any gas tube length and any configuration, from classic 20-inch barreled 5.56mm M16 clones to .300 Blackout AR pistols. It is a no-frills item, ideal for use as a backup BCG or as the primary BCG of a budget AR-15 build.
6. JP Enterprises Complete JPBC Bolt Carrier Group
Few companies in the United States are as synonymous with quality as JP Enterprises. JP specializes in high-performance AR-15 firearms and parts for competition use. The line of JPBC bolt carrier groups is intended for use on lightweight AR-15 builds.
The JPBC BCG’s heart is the innovative JP LMOS low-mass carrier, eliminating most of the reciprocating mass from the AR’s cycling.
This system significantly cuts down felt recoil, increasing sight recovery speed and allowing shooters to make much faster follow-up shots.
This BCG also features the JP Enhanced Extractor and Ejector, improving your rifle’s extraction pattern while mitigating brass damage and smearing. Ideal for the reloader who needs to preserve the life of their casings.
Several configuration options are available. You may order the JPBC with or without a bolt installed in one of three finish options: QPQ black, polished silver-colored stainless steel, or anodized gold.
All parts of the JPBC BCG use SAE 9310 steel and feature diamond-like coating (DLC) for enhanced surface hardness and lubricity. Variants with the bolt pre-installed feature the JP Enhanced Bolt, a proprietary bolt offering higher reliability than standard mil-spec bolts.
7. Rosco Manufacturing 5.56/.300 BLK Bolt Carrier Group
Rosco Manufacturing may be a lesser-known company based out of Rhode Island, but they are committed to manufacturing quality products out of the best raw materials available. The company’s area of expertise is AR-15s and AR-15 parts, in particular barrels.
The Rosco Bolt Carrier Group is the same BCG as the one featured in their complete Purebred and Bloodline AR-15 firearms. It prominently features the Rosco dog logo on the right side, distinguishing it from other manufacturers’ BCGs.
This BCG is fully mil-spec, featuring a 9310 steel bolt, shot peened, High-Pressure Tested (HPT), and Magnetic Particle Inspected (MPI).
Rosco BCGs are compatible with all mil-spec AR-15 upper receivers and barrels but best function with Rosco AR-15 5.56mm, .223 Wylde, and .300 Blackout barrels, offering a perfect match with these products.
8. Bravo Company Manufacturing Bolt Carrier Group MPI
Many gun owners consider BCM to be the go-to manufacturer for AR-15 parts. The BCM Bolt Carrier Group is a mil-spec compatible BCG, suitable for use in all 5.56mm and .300 AAC Blackout builds. It features a properly staked gas key, secured in place with industry-standard Grade 8 fasteners.
All parts are machined to military specifications, with a bolt assembly manufactured from Carpenter 158 steel, the same type used in the original select-fire rifles such as the M4 or the M16. The gas key is chrome-lined and heat-treated to provide the durability you expect of a fighting rifle.
The bolt assembly features a robust, machined tool steel extractor, a high-strength BCM extractor spring, and is appropriately High-Pressure Tested (HPT) and Magnetic Particle Inspected (MPI).
Why is the Bolt Carrier Group Important?
In the AR-15, the bolt carrier group is the name of an assembly of different parts found in the upper receiver. The BCG is necessary to perform most of the actions required to operate and cycle an AR-15.
The elements of a BCG are:
- Bolt carrier: The bolt carrier is the largest BCG element, holding all the other parts in place. When firing a cartridge, a small amount of the gases generated are redirected back into the receiver, pushing the carrier rearwards and allowing the action to extract the spent case. In turn, the bolt carrier is pushed back by the AR-15’s buffer spring (situated into the buffer tube, which holds the stock), allowing it to chamber a new cartridge. This process repeats with every cartridge fired until the magazine runs dry, at which point reloading becomes necessary.
- Bolt: The AR-15 fires from a closed bolt, which locks into place when a cartridge is chambered. The bolt is designed to rotate about 22.5° and features several teeth called bolt lugs, designed to engage with recesses into the barrel extension. The bolt is the primary pressure-bearing part; it has to resist the high pressure generated by a 5.56mm cartridge (over 62000 psi). Certain AR-15s need a bolt with different dimensions to fire cartridges with larger case head dimensions, such as 7.62x39mm.
- Ejector and extractor: The ejector is a spring-loaded plunger into the bolt face, which appears as a circular button when inserted, and the extractor is a claw on the side of the bolt. When the bolt is moving rearward, the ejector’s function is to push on the head of a spent case, while the extractor claw grabs onto the case groove, allowing it to fling the case out of the receiver.
- Firing pin: The firing pin is a long, thin, rod-shaped piece of hardened steel retained by a spring. At rest, the firing pin sits in the center of the bolt. Pulling the trigger releases the hammer, hitting the back of the firing pin with enough force to briefly overcome the spring, allowing it to strike the primer of a cartridge, firing it in the process. The spring then pushes back, returning the firing pin to its resting position.
- Gas key: The gas key is the long cylindrical tube protruding at the top of the BCG, staked in place with a pair of screws. The AR-15 uses what is called a direct impingement system. Instead of using a piston to push the bolt back, the gases are redirected into a gas tube, leading into the gas key and directly inside the bolt carrier group, pushing it rearwards.
- Gas rings: The gas rings are located inside the bolt assembly, acting as a seal to prevent the gases brought into the bolt by the gas key from bleeding outside of the BCG. Worn or missing gas rings may result in malfunctions.
Replacing a bolt carrier group requires partial stripping of the upper receiver, but anyone can do it in a matter of minutes with practice. If any part of your current BCG were to break, wear out, or malfunction, having a spare BCG allows you to continue shooting.
Upgrading your BCG can also be done to reduce the chances of malfunctions or improve its durability and reliability, making your AR-15 more dependable.
.300 Blackout AR-15 platforms do not need a caliber-specific bolt carrier group, allowing shooters to choose from the full range of .223/5.56 models. Certain BCGs may be marked .300 Blackout, but they are functionally no different; the markings only exist for safety and identification purposes.
Additionally, all the bolt carrier groups on this list are referred to as “M16” or “Full-auto” BCGs. Despite the name, they do not turn your AR-15 into a machine gun and are legal to own.
A full-auto bolt carrier group possesses an additional cut in the rear part of the carrier, intended to trip the sear of a fully-automatic or burst-firing mechanism.
In a military rifle set to semi-automatic mode, and on all civilian-legal, semi-automatic platforms, this does not occur.
Semi-auto only BCGs are less and less common, heavier, and less desirable than mil-spec full-auto BCGs.
The Bottom Line
When building a .300 Blackout AR-15, select the highest-quality parts possible for your applications, particularly if you intend to build a firearm for home defense.
No-frills mil-spec BCGs are ideal for budget builds or for assembling your first .300 blackout rifle.
AR-15s intended for high-volume shooting function best with BCGs featuring finishes and coatings with high abrasion resistance.
Reduced-weight BCGs are best suited for rifles intended to be carried all day, from duty use to competition.
