The Best AR-15 Bolt Carrier Groups (BCGs) 2024

Building your own AR15 can be extremely fun and rewarding but it’s not the easiest of tasks. there are many different parts you will need to select as you build your AR15.

AR15 build kits can make the building process much more manageable and hassle-free. These build kits come in many varieties. One kit could contain just a few parts for one section, while another kit could include almost all the parts needed for the entire rifle.

Our Guide to the 5 Best AR-15 Bolt Carrier Groups (BCGs) Reviewed

In this article, I’ll cover what components are needed to build the upper receiver, and how upper parts kits can make the assembling process smoother. I’ll also reveal what you need to know to confidently choose the best upper parts kit.

Knowing which upper parts kit to choose can be confusing. Which kit you buy essentially comes down to what parts you need. To make this clearer, I’ve picked out the best AR15 upper parts kits currently on the market. I’ve tested and reviewed each kit to help you choose which one is right for you.

Why Should You Upgrade Your AR-15’s BCG?

Upgrading your BCG offers you several benefits. First, it negates one of the most common failures on your rifle: failure to extract cartridges. A top-of-the-range BGC also makes your rifle easier to clean and maintain.

The BCG is put under more stress than most other parts in your AR-15, which leads to significant wear over time. Upgrading your BCG will greatly reduce the chances of your rifle going bye-bye in the field.

FInally, the BCG is one of the most affordable upgrades you can make on your rifle. If you’re looking to get some easy wins between more expensive upgrades, then this is certainly one to consider.

Best Bolt Carrier Group Components

The BCG has six major components, including the carrier, bolt, gas key, firing pin, cam pin, and a retaining pin.

Carrier

This refers to the external cover for the bolt that is attached to the gas key. Regular cleaning and inspection are crucial to ensuring that the screws keeping it in remain firm.

Bolt

The bolt is essential in guiding the next round into the chamber, as well as ejecting the used cartridge after firing. Typically, the bolt is made of Carpenter 158 or 9310 Steel and consists of gas rings, an ejector, a bolt face, extractor, bolt body, and lugs.

Gas Key or Bolt Carrier Key

This funnels gas from the gas tube into the carrier. It has to be tight and staked to create a seal. Correct staking maintains the firmness of the screws.

Firing Pin and Retaining Pin

This is the round protrusion that hits the primer of a cartridge, which in turn, sets off the priming component and detonates the powder. The retaining pin is located near the rear of the bolt carrier group inside a little notch in the bolt carrier.

Cam Pin

The cam pin retains the bolt in the bolt carrier and keeps the bolt and firing pin in line. It also keeps the bolt in a locked position as the BCG completes its forward drive into the battery. The cam pin performs several functions that are essential for a firearm’s operation.

Choosing the Best Bolt Carrier Group for Your AR

The bolt carrier group is the core element of an AR15. It goes without saying, then, that it has to function perfectly. There are some important things to consider when choosing a BCG for your AR-15 rifle.

Bolt Material

This should be your primary concern. While BCGs are usually made of steel, they are also available in titanium, aluminum, and hybrids. The most popular steel alloys for BCGs are Carpenter 158 and 9310 steel.

The BCG encounters plenty of stress and heat, which makes steel an ideal material. 9310 steel is strong and durable, making it common among manufacturers. Carpenter 158 is more commonly used by the military.

Heat Treatment

Your BCG should be heated-treated and processed for top performance. Heat treatment repeatedly exposes the steel to high temperatures and cools it to impart tensile power and remove weariness.

Internal Chrome Coating

Mil-specs require the BCG to be chrome-coated. This is to give it a smoother, rust-resistant internal surface. This increases the BCG lifespan and makes it easier to clean. Many manufacturers overlook the internal coating.

Weight

Weight should always be an issue to consider. Selecting a lightweight BCG can mean a considerable weight variance (up to six ounces).

Other than taking some of the weight off your rifle, lightweight BCGs can improve accuracy. The BCG leans towards the shooter after firing a shot, so having a slighter one will allow you to place cleaner follow up shots.

However, low-mass BCGs force you to adjust your rifle and limit the types of ammo you can use.

How Does an AR-15 BCG Work?

When you fire a round, some of the gas from the explosion is fed up the gas tube in your barrel and is propelled back into the BCG. This force pushes the bolt back and forces the spent cartridge out of the ejection port.

The bolt being pushed back allows the springs in your magazine to push a new round into the chamber. This process is what allows your rifle to fire in semi-auto. It sounds simple, but it was a revolutionary discovery in the old days.

Fully Automatic vs. Semi-Automatic BCG

Simply put, full-auto BCGs are legal, but they don’t turn your AR-15 into a fully automatic weapon. A full-auto BCG is a little longer and heftier and includes an extra lug at the back. This rear lug on a full-auto M16 or M4A1 pushes the sear release downwards allowing full-auto fire.

In a semi-auto AR-15, the rear lug does not affect how the gun works. Semi-auto BCGs include an additional cut that extracts some weight that assists with reliability. Semi-auto BCGs used to be more popular because they were cheaper, but this is no longer the case. Given the option, go full-auto.

M16, AR-15, and Lightweight AR-15 BCGs

A full-auto (M16) BCG is the most popular on the market today. M16 BCGs work in both AR-15s and M16s.

Lightweight BCGs are the latest addition to the market. Compared to their semi-auto and full-auto cousins, they weigh much less at about 5.75 ounces. They’re best for shooters looking to lose some unnecessary weight.

What differentiates the three BCGs is the full-auto lug below the BCG part that touches the sear release, setting into full-auto mode. However, the standard AR-15 or lightweight AR-15 has no trigger components for full-auto firing.

Materials

Bolt carrier groups (BCGs) are available in many materials which determine their durability, reliability and cost.

Steel Bolt Carrier Groups

Steel is a common BCG material for AR-15s, and other guns due to its durability, reliability, and affordability. Nearly all steel BCGs are machined from 8620 steel. Exceptions include Carpenter 158 for carriers and 416 stainless steel (for low-mass BCGs).

Titanium Bolt Carrier Groups

Titanium BCGs (mostly 6AL-4V) are lightweight with the reliability and robustness of steel. This material has a higher resistance to corrosion and breakage, especially when sprayed with nickel boron for hardening. It’s also very expensive.

Aluminum Bolt Carrier Groups

Aluminum is almost 40% lighter than titanium, thus common in lightweight BCGs. It reduces recoil and offers accurate follow-up shots. However, aluminum BCGs wear quickly.

Hybrid Bolt Carrier Groups

These BCGs are made from a blend of the materials mentioned above. The BCGs offer reduced weight and increased strength, making them more expensive.

AR-15 BCG Finishes and Linings

AR-15 BCGs have many different finishes, including hard chrome, phosphate, black nitride, nickel boron, Diamond-Like Carbon (DLC), Titanium Nitride, and Robar NP3+.

• Hard Chrome finish BCGs are best suited for the harsh environment in which BCGs usuallyoperate. It’s hardness makes it durable, and it has natural lubricity. It’s also corrosion-resistant. However, they are rare and quite expensive.
• Phosphate finish is common in Mil-spec BCGs and includes an internal chrome lining in the gas key. Compared to hard chrome, it’s cheaper and less glossy, ideal for military guns. Most people recommend it for the rough finish and superior lubricity.
• Black Nitride (Melonite or Salt Bath Nitride) undergoes heat treatment for hardening. It’s corrosion-resistant, smooth and slick. It’s one of the easiest to clean.
• Nickel Boron has a superior metal finish that provides durability, less friction, and corrosion resistance. It has high lubricity.
• Ionbond DLC is a superior metal finish applied via a PVD (physical vapor deposition) process. It’s durable, corrosion-proof, and with excellent low-friction properties, making it more expensive.
• Titanium Nitride, an aerospace and military special alloy, is a sturdy ceramic material that increases maintenance and edge retention. The finish has outstanding lubricity, rigidity, and corrosion resistance. The gold appearance is just one of the reasons it’s more pricey.
• Robar NP3+ is electroless nickel-based steel, aluminum alloys, and stainless-steel finish. It’s durable, very smooth, corrosion-resistant, and has dull-gray finish. It’s also quite costly.

AR-15 BCG: HPT and MPI

High Pressure Tested (HPT) and Magnetic Particle Inspected (MPI) means that every bolt is separately assessed at a proof load. It’s usually written on the bolt, though not always. If the description doesn’t include this, then you have to assume it’s only batch tested.

Whether you’re using your AR-15 for self-defense or hunting,you should always go for a BCG that is HPT and MPI tested.

AR-15 BCG Features

Shot Peening

Shot peening refers to a method in which miniscule metal pellets are shot at the steel to release stress from the metal. This process makes a BCG durable and better quality. It also improves the bolt carrier and bolt’s fatigue performance.

The surface of the material must produce tension to create a dimple, as the material below the surface tries to reinstate its unique shape. This produces a hemisphere of cold-worked material that is very stressed in density below the dimple.

Shot peening extends the life of the BCG significantly.

Staking

The BCG goes through massive gas pressure whenever a shot is fired. The gas key is fastened to the carrier via two hex screws to stop gases from escaping. The screws are staked (smashed side metals) to prevent movement from the high gas pressure.

This also excludes the probability of any unintended malfunctions.

Fasteners

When locking the gas key to the bolt carrier, it’s vital to remember the fastener’s shear and tensile strength. Therefore, fasteners must be durable enough to endure frequent stress.

The standard fasteners for BCGs (in the AR-15) are grade eight and have an estimated tensile strength of 150k lbs./sq. inch. Grade five fasteners have a 120k lbs./sq. inches in tensile strength. I would recommend a BCG with grade eight fasteners or

How to Install an AR-15 BCG

Make sure that you have all the necessary accessories and parts, as mentioned in the review above. Then, fetch the only required tool, a screwdriver.

1. With the wide side facing out, insert the bolt into the bolt carrier.
2. Turn the Bolt and ensure that the bolt carrier opening (beneath the carrier key) is aligned with the larger opening.
3. Insert the cam pin via the bolt carrier opening and into the Bolt to align the bolt carrier with the flat bar on the cam pin’s top.
4. To extend the bolt, pull it back and turn the cam pin 90⁰.
5. Drop the firing pin (facing side down) from the bolt carrier’s opposite end and seat it by pressing it down.
6. Insert the firing pin and the retaining pin in via the bigger opening on the similar side of the bolt carrier you inserted your cam pin from.
7. Insert the charging handle into the appropriate cut out notch in the upper receiver.
8. Make sure that the bolt remains extended in the carrier and place it into the charging handle with the carrier key offering the alignment.
9. Press everything home and listen for the audible click of the charging handle seating.

The Best AR-15 Bolt Carrier Group

While sticking within your budget is important, you should never compromise quality to save a few bucks. Sometimes you just need to make that sacrifice for the best, right?

For durability and maintenance purposes, shot peening, MPI and HPT testing should be considered. Fasteners and staking for the gas key are vital for safety.

Our winner in this roundup is the Brownells Titanium BCG. It’s made of high-grade steel 9310 and 8620, making it reliable and more durable. The titanium nitride finish is exceptional, yet the BCG is affordable. Plus, it’s a full-auto BCG, making it the full-package option for your AR-15 rifle. The reduced recoil makes shooting easy, even for novices.