Everything You Need to Know About an AR-15 Bolt Carrier Group

The AR-15 is a thing of beauty. It’s reliable, lightweight, and very fun to shoot. Its customizability has made it a favorite among collectors, hobbyists, and competitors everywhere.

The most important thing to consider when buying or modifying one is the AR-15 bolt carrier group. This system is the heart and soul of your weapon, so it’s crucial to understand what it is. You need to consider build, material, operation, preference, and competing systems when deciding.

Whether you’re an AR-15 veteran looking to brush up, or a new owner looking for clarity, never fear. Read on for everything you need to know about AR-15 bolt carrier groups.

What is an AR-15 Bolt Carrier Group?

AR-15s are often called one of the most versatile guns. They are fully modular and put almost total control in the hands of the user. The bolt carrier group, in particular, is the most important part of this platform.

A bolt carrier group in essence is the main mechanism that allows the gun to operate. It’s often known as the heart of the rifle. The bolt carrier group, or BCG for short, is like the engine of your AR-15.

The BCG makes sure the striker works, the spent casings eject, the hammer recocks, and a new round loads. The basic cycling of the gun wouldn’t work if something happens to the bolt carrier group.

The AR-15 Bolt carrier group is lightweight and designed to be semi-automatic only. Options like M-16 BCGs are available and compatible with AR-15 platforms but have their own caveats.

The AR-15 vs. M-16 Bolt Carrier Group

There are two main configurations for bolt carrier groups in the AR-15 class. These are the AR-15 BCG and M-16 BCG, both of which you can use in an AR-15. The M-16 bolt carrier group was the gold standard for a long time, but the AR-15 is always popular.

The M-16 bolt carrier group is heavier, with more mass near the rear. The reason for the heavier build is the M-16 is a full-auto weapon. For improved reliability under high stress, the M-16 BCG is the preferred model.

Moreover, the AR-15 is a semi-automatic weapon by design. The AR-15 bolt carrier group keeps this in mind and doesn’t allow full auto without significant alteration. Using an M-16 BCG in an AR-15 build will work, but won’t make it full-auto.

This difference in bolt carrier groups has caused plenty of debate in the AR-15 community.

How does a Bolt Carrier Group Function?

The bolt carrier group has several parts. There is the bolt itself, the firing pin, extractor, gas key, and cam pin, which all sit in the upper receiver. The BCG is responsible for chambering a new round, cycling the action, ejecting the empty case, and resetting the hammer.

This all has to happen in a single cycle to keep the gun operational. Any hiccup and you’ll have a failure to fire or a dangerous malfunction. For your AR-15 platform to function it needs enough mass to finish the cycle.

This mass comes from the buffer and the bolt carrier group itself. The total weight and its distribution will affect how the weapon performs. With heavier set-ups expect more muzzle climb and higher recoil.

The reason this weight is necessary is because of how the gun cycles. When the hammer strikes the firing pin, the racing bullet creates gas. As the bullet exits, this gas gets sucked into the gas port.

It passes through the gas block and then heads down the gas tube towards you. The gas enters the interior of the bolt carrier via the gas key at the rear of the gas tube. All of this energy entering the bolt carrier group will push the bolt backward.

The bolt needs to push hard against the buffer and spring in the receiver extension to eject the spent case and load another round. The weight helps ensure the BCG cycles with enough force.

Varying Build Considerations

There are several factors that impact how well a bolt carrier group performs. Material plays a role, as the weight of steel tends to make it king. The type and quality of your ammunition is also a big deal since it can contribute to misfires and fouling.

You should also consider how long the entire gas system is in comparison to the barrel length. The difference in length between carbines and long rifles is major. Longer barrels create more energy.

This is because the bullet stays longer in the barrel after it goes by the gas port. This in turn affects how much gas makes it back to the action, with more giving a bigger kick of power. The actual size of the gas port can also affect this.

Additionally, the materials and resistance found in the combination of buffer and spring are important. Whether by sheer power or creative engineering, the BCG uses pressurized gas to cycle.

Which AR Bolt Carrier Group Is Better?

Many argue that the AR-15 bolt carrier group is a revelation in rifle operation. Its lighter weight design transfers less shock to the user. This leads to increased comfort and stability.

In theory, it also allows for longer sustained fire without fatigue or inaccuracy. The downsides are of course the AR-15 is semi-automatic, and is always milled this way on purpose. Diehard M-16 fans don’t like the lack of full-auto flexibility.

They also argue that the lighter design of the AR-15 bolt carrier group is actually a bad thing. A common argument is that the added weight of the M-16 bolt carrier group actually helps with stability. Additionally, the slight difference in mass doesn’t make aiming difficulty any different.

The heavier steel M-16 bolt carrier group also takes longer to cycle. This actually lowers the chance of malfunction as it gives the brass more time to eject. This also reduces the stress and damage placed on the casing itself, making it a bonus for reloaders.

You’ll often hear arguments that the M-16 is more reliable, less likely to malfunction, and more powerful even as semi-auto. AR-15 believers would counter many of these arguments. Smooth operation, less muzzle movement, and lower recoil are all hallmarks of the AR-15 BCG.

Does the Material Matter?

M-16 bolt carrier groups are often made with heavy steel. AR-15 BCGs on the other hand are lightweight titanium or aluminum. The titanium used in AR-15 bolt carrier groups is around 40% lighter than the steel found in M-16 BCGs.

The yield strength of titanium BCGs is actually comparable to the M-16 steel ones. They do lose a bit when it comes to overall tensile strength, but this isn’t a major issue. If you notice deformation, you should already be replacing it before it malfunctions.

Aluminum is cheaper and approximately 40% lighter than titanium. It’s weaker of course, but it isn’t designed for defense or durability. Aluminum bolt carrier groups are like the fancy race car parts of the gun world.

They’re designed for competition shooting in ideal conditions, with ideal storage and ammunition. They also require lots of maintenance, regular cleaning, and oiling. Aluminum is often for the high-end hobbyist and sportsman.

When it comes to steel, there is an argument that the M-16 packs more bang. This allows it to power through poor conditions or even while fouled up. It should also hold up in most unfavorable conditions, especially compared to aluminum.

However, that doesn’t relegate the AR-15 to only sterile competition environments. A high-quality AR bolt carrier group can stand up to plenty of abuse, especially if it’s titanium.

State Laws and Semi-auto Vs Full-auto

Before you buy a new AR bolt carrier group, there are a few legal and operational things you should consider. One of which is the difference between full-auto and semi-auto. It should come as no surprise that across the U.S. there are tons of rules and regulations regarding guns.

M-16s and M-16 BCGs are actually for full-auto use, which isn’t legal in every state. Washington and New York are 2 of the 8 states where full-auto weapons are illegal, while California only recently overturned a general AR-15 ban. This means that although you could get your hands on an M-16 bolt carrier group, you may not be able to make full use of it.

It is worth remembering that you can still use an M-16 BCG in a semi-automatic AR-15 setup. For owners in restricted states, this option may be desirable for personal preference. However, you should know that modifying either the BCG or platform to allow full-auto could be a criminal offense depending on the state.

The AR-15 Bolt Carrier Group Is the Heart of Your Weapon

Despite the competition, it’s clear the AR-15 bolt carrier group isn’t going anywhere. From hobbyists to competition shooting and everything in between, it’s a solid option. Moreover, the flexibility and choices mean there’s something for everyone.

If you still have questions or are looking for additional advice, then check our site. We have plenty of information available.

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