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Bolt Carrier Group – Do You Really Know What It Is?

When it comes to talking about firearms, one thing is certain – they must come with proper rifle mechanics in order to perform well. For example, the bolt carrier group is considered to be the heart of the AR-15.

Therefore, you can’t expect such a powerful rifle to work without a BCG – bolt carrier group. However, do people actually know what a BCG is? As you may know, this piece of the AR-15 is often a misunderstood but critical part of the firearm.

Given its importance, you must know more about the bolt carrier group – after all, you may even have to buy one in the future. So, in today’s article, we’ll talk about everything that needs to be known about the infamous bolt carrier group.

The Breakdown of the Bolt Carrier Group

Naturally, we’ll start with the beginning and introduce you to the components of a BCG. There are seventeen parts that make an AR-15 bolt carrier group:

  • Bolt
  • Ejector
  • Ejector Spring
  • Ejector Roll Pin
  • Extractor
  • Extractor Pin
  • Extractor Spring
  • 3 Gas Rings
  • Bolt Carrier
  • Bolt Cam Pin
  • Bolt Carrier Key
  • 2 Bolt Carrier Key Screws – these screws attach the bolt carrier key to the bolt carrier itself.
  • Firing Pin
  • Firing Pin Retainer Pin

How Does the Bolt Carrier Group Work?

Obviously, the pieces within a bolt carrier group are nothing without the operations that they have to do in order to ensure the proper functioning of the rifle. In this respect, the bolt carrier group is responsible for the following eight basic operations:

  1. Initially, the bolt is found in its rearmost position. Then, the action spring pushes the bolt forward and, during this movement, it picks up a bullet from the clip/magazine and then pushes it inside the chamber, with the help of the feed ring.


  1. When the bolt carrier itself moves forward, the bolt is passing through cuts within the barrel extension and a cam pin will cause the bolt to rotate. Therefore, the locking lugs on the bolt will be locked as the bolt reaches the forward-most point of its movement.
  2. When the trigger is pulled, the sear will release the hammer. Then, the hamper spring will rotate the hammer via force, all the way back into the firing pin. Ultimately, the firing pin will pass through a hole in the middle of the bolt carrier – as a result, the bolt and one of the pointy ends of the firing pin will strike the primer of the cartridge, thus firing the weapon.


  1. Then, while the bullet leaves the barrel, some of the gases that remain behind it will be trapped into a gas tube. The hot gases will travel down the tube, through the bolt carrier key and then redirected forward so that they push the gas rings on the bolt. This movement will then push the bolt slightly forward and the carrier to the rear. The movement of the carrier pushes against the cam pin which caused the locking of the bolt. Lastly, the bolt will rotate in the opposite direction and unlock the previously locked lugs – the bolt will then be free to move backward.


  1. During the backward movement of the bolt carrier group, the extractor will remove the old cartridge case from within the firing chamber and pull it backward.


  1. As the backward movement continues, the bolt carrier will also re-cock the hammer.


  1. When the bolt goes past the ejection point, an ejection spring will force the empty cartridge case to be pushed from the extractor and outside of the ejection port.


  1. When the bolt reaches its rearmost point, the action spring will push the bolt forward once again, and the entire cycle will repeat itself.

As you can see, there are a lot of things going on when the firearm actually fires a bullet. Therefore, it goes without saying that one or more of the parts mentioned above can malfunction or act a bit weird, so to speak.

Common Bolt Carrier Group Issues

When you consider a firearm with proper rifle mechanics, you also have to take into account the fact that the weapon itself – and its components – have to be inspected and taken care of.

In this respect, you may want to know what could go wrong with some of the components of your weapon’s bolt carrier group.

  • Loose Gas Key

Keep in mind that the gas keys of the bolt carrier group can come loose. Their screws should be staked in place and, if this process is done correctly, they will take a lot of time to loosen.

However, such a thing can still happen. Loose gas keys result in a poor seal that allows gas to escape. This can, in turn, lead to cycling issues – failure to eject, as well as short-cycling of the bolt.

  • Bad Rings

The gas rings of the bolt carrier group are used to create a seal between the bolt carrier and the bolt. The seal contains the gases and, essentially, drives the entire system.

If any of the gas rings get damaged or worn out to the point where gases can escape, malfunctions similar to those caused by loose gas keys can appear.

  • Split Bolt

The cam pin hole is one of the bolt’s weak points. It comes with the least amount of material that has to withstand the firing and cycling of the BCG. As a result, you can be faced with a split bolt.

When you check the bolt carrier group – or some of its pieces – it is recommended that you take a look at the cam pin hole as well. You should be looking for any signs of excessive wear or fractures.

Naturally, these are only a couple of the issues that a bolt carrier group could experience. This is why you should schedule maintenance for your firearm, as well as for its BCG – still, you shouldn’t run checks on it very often.

The bolt carrier group doesn’t require a regular maintenance schedule. Also, the parts within it can be easily changed when they break or when you feel like it. On top of that, you can also change the BCG entirely.

The Bottom Line

Now, it is safe to say that you really know what the bolt carrier group is. Basically, it is the part of your weapon that helps it shoot bullets – if we may put it that way.

As mentioned at the beginning of this article, the BCG can really be seen as the heart of any AR-15 – or M16. Obviously, this calls for proper maintenance. Regular maintenance may not be required, but you should be taking a close look at the BCG once in a while – just to be sure th

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