Bolt Carrier Groups 101: AR-15 vs M16 BCGs

Bolt Carrier Groups 101: AR-15 vs M16 BCGs

Posted by STNGR USA on Jan 6th 2023

Bolt Carrier Groups 101: AR-15 vs M16 BCGs

Hey folks, it's Rick Barrett and in this video, we're gonna be talking about BCGs, otherwise known as bolt carrier groups.

What Makes Up a Bolt Carrier Group (BCG)?

Now a bolt carrier group is not a single component. In fact, it's made up of a bunch of different components.

Within a single bolt carrier group, you'll find a carrier key, the bolt carrier, the bolt gas rings, bolt, extractor, firing pin, cam pin, and the firing pin retaining pin.

Image from Gun Builders

Where is the BCG on the actual AR-15? That's a good question, it's right here in the upper receiver. That's where the bolt carrier is.

If you need a refresher on the parts of the components of the AR-15 upper receiver, check out this ultimate AR-15 resource.

How Do You Remove a Bolt Carrier Group (BCG)?

The way you remove a bolt carrier group on an AR-15 is to take the charging handle, pull it all the way back until the bolt carrier group is completely exposed and it should just drop out.

What Does a Bolt Carrier Group (BCG) Do?

The bolt carrier is the meat of the bolt carrier group. It is the primary housing that contains all the other important stuff: the firing pin, the gas key, cam pin, extractor, and bolt.

The bolt carrier is what contacts the buffer in the spring. It also absorbs a ton of force as gas expands inside the carrier. To handle this pressure and heat safely, the bolt and the carrier are made from three types of forged steel.

AR-15 vs M16 Bolt Carrier Groups

Now there are two different types of bolt carriers that you may run into when you're finding one on the after market. There's an M16 and an AR-15 version of the bolt carrier group.

M16 Bolt Carrier Group


The first one, the M16 BCG, will work in both the M16 and the AR-15. In fact, an M16 or a full auto bolt carrier group is the most common one you will find on the market. I must stress that if you put a fully auto rated bolt carrier group in your AR-15, it will not make it an automatic rifle.


The AR-15 bolt carrier groups are very rare find these days. They were more popular when companies didn't want to have that fully auto designation attached to their bolt carrier groups.

The main difference between the two is a full auto lug. The bottom portion of the bolt carrier group has a lug that contacts the sear release in a full auto trigger group and allows the gun to fire in fully automatic. Since the standard AR-15 does not have those components, that auto lug does not allow it to fire in fully automatic.

The only benefit of getting a semi-automatic bolt carrier group is that you'll find it at a lower price. So if you are looking to add a bolt carrier group to an AR build or maybe an aftermarket bolt carrier group, you're more likely going to go with the full auto bolt carrier.