AR-15 BCG Part 1: Field Stripping the Bolt Carrier Group

The BCG (bolt carrier group) for an AR-15 is one of the least talked about parts of an AR rifle. But it’s also one of the most important parts and should be well maintained. When you look at an AR-15 you notice the color, style of handguard, barrel, muzzle device, and stock. A lot of people don’t pay much attention to the BCG because it’s just an internal part. That part however is the equivalent of the motor in a car. It’s important and should be serviced from time to time. In two parts, we will be covering the entire BCG.

AR-15 BCG
The BCG (bolt carrier group) is often overlooked during maintenance and cleaning. But it is the engine of the rifle and should not be neglected.

For the most part, if you clean the BCG and keep it oiled, it will run for a long time without issues. Inspecting it during each cleaning is important for identifying issues that may be creeping up. This could include wear on certain parts or hairline cracks in the bolt. I once took the bolt out of a rifle at my agency and found part of it had chipped off and was gone. It was magically still firing, but I wouldn’t call it reliable at that point.

I have covered the importance of inspecting an AR-15 before, but in this AR-15 BCG series, we will focus on the BCG and disassemble the bolt components.

About the Bolt Carrier

Referred to as the bolt carrier group, the bolt carrier holds the bolt, gas key, firing pin, and cam pin. We will break it down step by step and talk about each part. The bolt carrier holds all this in place and allows several things to happen in just a fraction of a second when the gun is fired. There are several types of finishes available for BCG and some are better than others. We will talk about this briefly before we get into disassembling the BCG.

The first BCGs were chrome plated to make them durable. These types are still used today, but hard to find and expensive. The current mil-spec BCGs are phosphate coated which makes them hard but leaves a rough finish. This means the bolt carrier will need more oil to run smoothly. Black Nitride is one of the more popular finishes because it is durable and the finish is slick, making it run smoothly in the gun. One of the most durable finishes you can get for an AR-15 without breaking the bank is Nickle Boron. This type of finish will last for years with heavy use and helps the BCG run smoothly inside the gun.

Other types of finishes include Diamond-Like Carbon (DLC), Titanium Nitride, and Robar NP3+. All of these finishes are extremely durable, but also expensive. The good thing about the design of the AR-15 is the BCG can be replaced in seconds. I know a lot of people who had something break on their bolt or carrier and instead of fixing it, replaced the entire BCG. But it can be fixed!

Disassembling the BCG

Taking the bolt and firing pin out of a BCG is easy and should be done every now and then for cleaning. I would recommend using a good gun cleaning mat for this part, a work rag, and a small pick from a gun cleaning kit. To remove the bolt from the carrier, use the pick to pull the retaining pin from the side of the carrier (see photo below). Once the retaining pin is out, the firing pin can be removed from the back of the bolt carrier.

AR-15 BCG
Bolt parts from left to right: locking lugs (green), cam pin (yellow), gas key (orange), retaining pin (blue), and area where the firing pin will be removed from (red).

With the firing pin and retaining pin out, the next step is to remove the cam pin. With the firing pin gone, the cam pin will turn halfway and then pull out. If it is not turned, the gas key will be in the way and not let it come out. After removing the cam pin, pull the bolt out of the carrier. This is how far the BCG comes apart during a regular field strip. When I have the BCG field striped, I take the opportunity to inspect it for worn or damaged parts. We will cover this process before moving on to disassembling the bolt in Part 2.

Inspecting the Bolt, Firing Pin, and Gas Key

With the BCG field stripped, I like to check the firing pin first. The firing pin is made of extremely hard metal and will last a long time. I like to clean it off and make sure there is no damage or wear to it. Then I inspect the bolt and locking lugs. The bolt is the most likely place to have fractures or cracks. These can be hard to see so I use a light to inspect the surface. The area around the cam pin hole is where I have found fractures before.

Field stripping the BCG
These are the parts you will have after field stripping the BCG.

After inspecting the bolt for cracks, I check the locking lugs. In Part 2, we will take off the extractor, ejector, and gas rings. The rings can wear down and need replacing after a lot of use. Another area I like to check is the gas key. If you start to experience cycling issues, this can be caused by gas problems from the key or gas tube. The gas key should not be loose, and the screws should be staked. Staking a screw is a small indention in the metal beside the screw which keeps the screw from turning and coming loose. If the key needs to be removed, I would recommend installing a new one and staking it again.

Staking an AR-15 gas key
Staking the gas key is important to make sure the screws do not come loose.

Come Back Tomorrow for Part 2

Now that we have taken the basic parts out of a BCG, we will move on to the bolt. This contains the extractor, ejector, and gas rings. These parts can appear to be difficult to get out, but with the right tools they are not hard. With everything removed, we will also cover cleaning everything before re-assembling them and placing the like new BCG back into the rifle.

Sheriff Jason Mosher is a law enforcement generalist instructor as well as a firearms and tactical weapons trainer. Jason graduated from the FBI-LEEDA (Law Enforcement Executive Development Association) and serves as a Sheriff for his day job. When he’s not working, he’s on the range, eating steak, or watching Yellowstone.

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