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A Complete Guide to Bolt Carriers for Your Gun

Once you’ve got your toes a little wet in the wide world of gun parts, you’ll start hearing terms like “M16 BCG,” “staked gas keys,” or even “bolt carriers.”

This means that you’ve made it through the main surface knowledge, and now you’re ready to learn about the functionality of guns, and your gun part options.

So, what does it all mean? No worries, you’ve come to the right place. Keep on reading for our full breakdown of what bolt carriers are all about.

AR 15 Bolt Carrier Group: The Basics

The AR-15 rifle’s bolt carrier group, or BCG, is often referred to as its “heart.” To fire a round and repeat the process, it consists of around six pieces.

Gun enthusiasts like geeking out over it since it is a highly technical feature of the AR-pattern weapon. In light of these considerations, this essay is geared toward intermediate AR shooters. Those who are contemplating a firearm upgrade but want further information. Here, we’ll explain what a bolt carrier group is, how it functions, and the various materials it’s made of.

The History of the Bolt Carrier Group

Eugene Stoner, the inventor of the AR-15 and founder of ArmaLite, created the BCG that we know today.

Stoner hoped to build a weapon that would outperform the AK using the AR platform. As long as the system worked in the same direction, he thought he could accomplish that goal.

Mechanical components and propellant gases all travel in one straight line, which theoretically makes the gun more accurate. It’s simpler to comprehend how an AR-15 works and why Stoner developed it that way if you keep that core principle in mind.

Understanding How Bolt Carriers Work

Once the trigger is pulled, the hammer rises from the receiver chamber and strikes the firing pin, which penetrates the primer on a cartridge that is chambered in the rifle.

The gunpowder within the casing is ignited by a minor explosion, causing gas to be released. Part of the gas that drove the bullet out of the barrel is collected in a gas tube at the end of the barrel.

The bolt carrier has a gas key attached to it through a gas tube. The gas pushes back the BCG.

Several things happen when your AR 15 BCG retracts. It begins by rotating and releasing the bolt from its holder. Then, the extractor draws back, expelling the spent casing from the chamber.

To begin with, the BCG pulls the hammer back to restart the motor. The BCG compresses the buffer spring as it slides against it.

Afterward, the spring, as it’s bouncing back and forth, feeds another round into the chamber. As soon as the bolt assembly is all the way forward, the rifle is ready to fire once again.

Breaking Down the Parts of the BCG

The BCG must carry out several tasks to fire semiautomatically.

However, even though the BCG appears as a single unit, multiple components must function together in fast succession to enable semi-automatic firing. Keep reading to learn more about how the locking bolt works.

Let’s take a closer look at what each component does.

The Bolt Carrier

The BCGs are the “meat” when it comes to a gun’s performance. In addition to the firing pin and gas key, the main housing also has a cam pin and an extractor and bolt. The buffer and spring link to the bolt carrier.

In addition, the gas expanding inside the carrier reduces the amount of force applied to the gasket. Manufacturers use three kinds of forged steel for the bolt and carrier to withstand the high pressure and heat: Carpenter no. 158, 8620, and 9310, respectively.

Gas/Carrier Key

The small protrusion on the bolt carrier known as a carrier key (also known as the gas key) harnesses the gas flowing from the gas tube.

The bolt and extractor are situated in a hollowed-out key that allows for gas to travel through it to reach the bolt and extractor. To spin the bolt and extractor, which secures and unlocks the carrier group from the firing chamber. Thus, gas must be passed through the system.

Bolt and Extractor

Despite their separate duties, the bolt and the extractor operate together as a team.

You can lock or unlock the BCG in the AR-15’s star chamber thanks to the spinning bolt’s “star” design at the front, which looks like a cogwheel. Locking and unlocking the chamber requires a rotation of roughly 15 degrees.

After each shot, the extractor grabs the rim of the round and pulls it out of the star chamber. A small ejector and spring within the bolt head exert pressure on the casing at the same time.

It is only after the casing is out of the chamber and into the buffer tube that the ejector’s spring pulls the casing out of its upper receiver. The bolt head and extractor can pick a new round as the carrier and bolt go forward.

Bolt Gas Rings and Pins

When you cock a bolt, there is a tiny gas ring on the bolt that acts as a seal to keep the gas from escaping into the upper receiver.

Next, we have the firing pin and a retaining pin.

The firing pin is inside the bolt. Next to the ejector, the pin’s head barely protrudes from the bolt’s head. Immediately after you pull the trigger, a high-flying hammer smashes against a pin on the rear of the carrier.

The head of the pin strikes the head of the bolt, which in turn, hits the primer of the round, causing it to go off. There must be some restriction on the movement of the firing pin in the BCG to prevent it from falling out and causing the primer to go off.

You put a tiny retention pin through the side of the carrier to prevent the firing pin from falling out of the bolt as the BCG moves forward.

Cam Pin

When the bolt is unlocked, the cam pin prevents it from turning excessively.

The cam pin is placed into a bolt hole via the carrier. The cam pin rides in a groove carved into the top of the carrier. The firing pin slides through a hole in the center of the cam pin.

This guarantees that the cam pin does not slip out of the machine. Another benefit is that it maintains all three parts of the firing mechanism operating as one unit.

Materials of BCG

BCGs come in a range of metals and coatings, but it’s not always clear what they have to offer in terms of advantages.

For the ideal BCG configuration, there is a lot of debate depending on individual performance requirements.


Steel is the primary material used in most BCG construction. Mil-spec steel is a more precise term that refers to the steel used in military firearms.

Aluminum and titanium are two more prevalent metals. Low-mass carriers are ideal for competition rifles and rifles with adjustable gas systems because of their minimal weight. Both titanium and steel are more expensive than steel, but titanium is more expensive.

Lightening cuts in the bolt carrier are an apparent method of reducing weight. Large pieces of metal are removed from the carrier during this process.

The idea here is that instead of employing pricey lightweight metal, simply use less metal. Again, low-mass carriers often use such a design approach.


To enhance the life of building materials, manufacturers finish their goods.

In the case of firearms, the finish has an inherent lubricity and enhanced durability. More durable and simpler to clean BCGs may be achieved by using high-quality coatings.

Consider how much you’ll be using your gun before deciding on a new one since they’re more costly.

Since BCGs may be finished in more than 50 distinct ways, we won’t go through them all here. Instead, we’ll focus on some of the most popular options.

Among them are phosphate, nitride, and Nickel Boron.

You’ll need to use more lubrication and clean it more often with phosphate, which is the normal mil-spec finish, but it’s more robust and resistant to corrosion.

Next, the smoothness of nitride is regarded as superior to that of phosphate. The downside is that it’s more expensive. As with phosphate, it has a brownish hue to it.

So we have Nickel Boron. At this point, you’re looking at some of the most expensive finishes. The stainless finish of a nickel boron BCG makes it very smooth and long-lasting. You can explore this well-rounded collection of BCGs at Rubber City Armory BCG.

Finally, we have DLC. The Diamond-Like Carbon is the best finish out there, period. It’s known for its long life and silky feel. A high-quality finish on a BCG doesn’t always boost your overall performance, but rather extends the life of the component itself.

Gun Accessories and Gun Parts: Simplified

There’s always a steep learning curve that gun enthusiasts have to go through to become real experts. We hope that our guide has shed some light on the nuances of bolt carriers and what makes them tick.

And, you should head straight to our hunting and recreational sections to read our other tips and explainers that will help you achieve true gun expertise.


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