Are you currently looking to install a new bolt carrier group on your AR-15? If so, you’ve come to the right place.
Best Right Handed Pick: Colt Factory Bolt Carrier Group
The Colt Factory Bolt Carrier Group is a solid choice for a mil-spec bolt carrier group. This is a durable BCG built out of parts that have been chromed lined and precision engineered for optimum quality.
Best Left Handed Pick: Toolcraft Logo’d Left Handed 5.56 Nitride MPI Full Auto Bolt Carrier Group
The Toolcraft is a solid pick for a left handed bolt carrier group. This bolt carrier group is built out of a very durable 9310 steel with a very rust and corrosion resistant nitride finish. It’s also built to mil-spec standards and is magnetic particle inspected to further ensure durability.
Best Overall Pick: Battle Arms Development AR-15 Enhanced Full Auto Bolt Carrier Group
The Battle Arms Development Enhanced Full Auto Bolt Carrier Group is a solid pick for an AR-15 BCG. Capable of handling fully automatic fire, the Battle Arms Development is built out of 8620 steel with a corrosion resistant nitride finish, and also comes CNC hardened for added durability.
The bolt carrier group is one of the single most important components to have in your AR-15 because it allows the rifle to fire and function to begin with. Without the bolt carrier group, your AR would be little more than a club.
Regardless of whether you are building a new AR-15 from the ground up with a building kit or seeking to upgrade your existing one, the bolt carrier group is arguably the component that deserves more careful research than anything else.
In this guide, we’ll outline and discuss the primary components of an AR bolt carrier group, how to install it in your AR-15, the top qualities to look for in a group, and then our choices for the top three best bolt carrier groups that you can get in 2021.
What Is The Bolt Carrier Group Comprised Of?
You’re probably wondering: what even is the bolt carrier group to begin with?
The short answer is that the bolt carrier group is a collection of components that reside within the upper receiver of your AR. As noted in the introduction, the bolt carrier group allows your AR-15 to fire in the first place, so without it your rifle is little more than a club.
Read also: Our guide on the Best AR-15 Side Charging Uppers
Also referred to as the BCG, the bolt carrier group uses the gas from a fired round to rotate and then push back against the recoil spring. This opens up the ejection port and also allows a spent shell casing to be ejected so a fresh round from the magazine can be stripped and loaded into the chamber to repeat the above process.
The bolt carrier is designed to twist first before it can move fully backward, permitting the rifle to cycle. The bolt carrier group also consists of the firing pin that strikes the primer to your round to enable the rifle to fire.
Let’s discuss the individual components of the bolt carrier group in greater detail.
The first part of the bolt carrier group is the bolt carrier. Take note that the terms ‘bolt carrier group’ and ‘bolt carrier’ are often interchanged, but the reality is that they are very different from one another. The bolt carrier itself is simply the housing that holds the rest of the parts of the bolt carrier group as a whole. To distinguish between the terms ‘bolt carrier group’ and ‘bolt carrier’ the term ‘bolt carrier housing’ is often used to refer to the latter.
The bolt carrier (or bolt carrier housing) is also in direct contact with the spring and the buffer to your AR-15. It absorbs the force from the fired round to travel backward, enabling the spent shell casing to be extracted and a new round to be loaded.
The next part of the bolt carrier group is the gas key, also known as the carrier key. The gas key is a small protrusion that is visible at the top of the bolt carrier housing. It is hollowed on the inside, permitting the gas generated from a fired round to travel into it so that the bolt and extractor can rotate. Without the gas key, the bolt carrier group as a whole could not rotate to cycle the action back.
The next part of the bolt carrier group are the bolt gas rings. The gas rings trap the gas when they expand from a fired round. Without the gas rings, the gas generated from a fired round would disperse.
The next components are the bolt and the extractor. Many people believe that these two terms are the same thing because they are part of the same unit. However, the truth is the extractor and the bolt are vastly different and serve two functions. The extractor hooks onto the rim of your round to hold it in place, before ejecting it out of the ejection port when your bolt travels to the rear.
The bolt is a star shaped piece that you will see at the front of your bolt carrier group. When the bolt carrier group needs to travel back, the bolt will rotate fifteen degrees to unlock the chamber as a whole, permitting the action to cycle backwards.
The last two pieces are the camp pin and the firing pin. As noted previously, the firing pin strikes the primer to your round to enable the AR-15 to fire. The cam pin, meanwhile, prevents the bolt from rotating too far when it unlocks. Specifically, the cam pin allows the bolt to rotate approximately fifteen degrees. You will notice the cam pin located in a hole through the carrier, and directly next to the bolt.
Looking for more buying guides? We got you covered with our article on AR-15 barrels.
Fully Automatic vs. Semi-Automatic Bolt Carrier Groups
There are two primary kinds of bolt carrier groups on the market: fully automatic and semi-automatic bolt carrier groups. If your bolt carrier group is a fully automatic version, it should be listed as such by the manufacturer.
A full auto bolt carrier group simply means that the group is durable enough to handle fully automatic fire. Meanwhile, a semi-auto bolt carrier group is only capable of handling semi-automatic fire.
As you can probably imagine, fully automatic bolt carrier groups are generally more durable. However, just because you install a fully automatic bolt carrier group in your AR-15 does not make it fully automatic. There are several other components you will need to add and adjustments to make to truly convert your AR-15 to a fully automatic design.
The main benefit to a fully automatic bolt carrier group is it permits you to make the necessary conversions for if you would ever want to convert your AR-15 into a fully automatic version (where and when it is legal of course). Furthermore, it may give you more comfort simply knowing that your AR-15 is capable of handling fully automatic fire.
Fully automatic bolt carrier group are slightly longer than semi-automatic bolt carrier group. The also feature a lug that applies pressure to the sear of a fully automatic AR, permitting bust or fully automatic fire. Yes, these features do make your fully automatic bolt carrier group than a semi-automatic version, so slightly more weight will be added to your AR as a whole. However, this should also theoretically help to reduce recoil as well especially in combination with a good AR-15 muzzle brake.
Fully automatic bolt carrier groups also come with shrouded firing pins in the absence of disconnector pins, permitting reliability with fully automatic fire.
All in all, fully automatic bolt carrier groups are generally longer, heavier, and more durable than their semi-automatic counterparts, and also slightly more expensive. A fully automatic bolt carrier group does not convert your AR-15 into a fully automatic version on its own, but it is capable of handling full auto fire if you choose to make the conversions in the future.
How To Install A New Bolt Carrier Group In An AR-15
Here is how to install a new bolt carrier group in your AR-15:
- Confirm the AR-15 is unloaded and remove the magazine
- Remove the rear pin to separate the lower receiver from the upper receiver
- Simply pull the existing bolt carrier group out of the rear of your upper
- Slide the new bolt carrier group into the upper receiver
- Reassemble the lower and upper and secure with a pin
As you can see, replacing the bolt carrier groups to your AR-15 is a very simple process. In fact, it’s one of the easiest components to replace.
Read also: Our article on the Best AR-15 Pistol Lowers
Buyer’s Guide For The Best AR-15 Bolt Carrier Group
These are the most important factors to consider when looking for a new bolt carrier group for your AR-15:
Magnetic Particle Inspected
Any bolt carrier group that you get for your AR-15 should come magnetic particle inspected. This means that the bolt carrier group was coated in a solution of magnetic particles and then inserted into a magnetic field created by electromagnets. This locates any cracks or fissures in the bolt carrier group, or otherwise confirms that no fissures or cracks exist.
The reason magnetic particle inspection is so important is because it confirms the durability of your bolt carrier group. Each time you squeeze your AR-15 trigger to fire a round, tens of thousands of pounds of pressure are applied per square inch. IF there are any cracks or fissures in your bolt carrier group, it simply will not hold up over the long term, let alone in the short term either.
High Pressure Testing
Besides coming magnetic particle inspected, your AR-15 should also come high pressure tested. This means that the round is capable of firing ammunition rated above SAAMI specifications.
Even if you do not plan on firing such ammunition through your AR, the fact that it can handle high pressure ammunition is a very welcome feature since it guarantees that the weapon can also handle standard factory ammunition without issue.
Drop-In Mil-Spec Design
Finally, if you want your bolt carrier group to come as easy to install as possible, it should have a drop-in mil-spec design. A drop-in design means that the bolt carrier group can be easily installed into your AR-15 without the aid of a gunsmith. The mil-spec design means that it will be fully compatible with most if not all other mil-spec AR-15 upper receivers on the market, which means that no fitting on your part should be required.
The 3 Best AR-15 Bolt Carrier Groups For 2021
Now that we’ve covered why you need to upgrade your bolt carrier group, here are the top three best AR-15 bolt carrier groups on the market for 2021:
Colt Factory Bolt Carrier Group
The Colt Factory Bolt Carrier Group is a solid choice for a mil-spec AR-15 bolt carrier group. Even though this is a Colt factory part, it should work in any other mil-spec AR-15 that you have as well. The fact that it has a drop-in design means that it can be easily installed in your AR-15 without the aid or services of a gunsmith as well.
The Colt factory BCG comes with multiple advantages, including a properly staked gas key, and a chrome lined gas key and carrier that are very durable and rust resistant. Each part is precision engineered as well.
The matte finish to the Colt factory BCG is admittedly not the nicest looking, but at the end of the day, if you’re looking for a solid mil-spec bolt carrier group that is built to last the Colt is a solid choice.
Just because it’s a Colt doesn’t mean that the Colt factory bolt carrier group can only be used in Colt AR-15s. This bolt carrier group will work in any mil-spec AR-15 in 5.56 out on the market. As an added bonus, it comes with precision engineered parts and is 100% American made.
- Colt factory part
- 100% American made
- Mil-spec design
- Parts are precision engineered
- Comes with a chrome linked gas key and carrier
- Drop-in design
- Comes magnetic particle inspected
- More expensive than many other bolt carrier groups
- Matte finish is not the most appealing
Toolcraft Logo’d Left Handed 5.56 Nitride MPI Full Auto Bolt Carrier Group
The Toolcraft Logo’d Full Auto Bolt Carrier Group is one of the best options for a left handed bolt carrier group on the market today. This is a full auto bolt carrier group, which means that it is strong enough to handle full auto fire (although it can just as easily be used for semi-automatic only rifles as well).
Specifically, the Toolcraft is built out of a very durable 9310 steel with a nice nitride finish for added rust and corrosion resistant. It’s built to mil-spec standards and is magnetic particle inspected to further ensure good durability. The gas key has also been properly staked and hardened to USGI specifications.
Of course, this is a left handed bolt carrier group, so it will not be an ideal choice for right handed shooters.
Overall, the Toolcraft is a solid pick for a left handed bolt carrier group. It’s capable of handling fully automatic finish and is very durable thanks to the 9310 steel build in conjunction with a nitride finish.
- Capable of handling fully automatic fire
- Has a very rust resistant nitride finish
- Built out of durable 9310 steel
- Gas key has been hardened to USGI specification
- Built to mil-spec standards
- Left handed only, so not an ideal option for right handed shooters
Battle Arms Development AR-15 Enhanced Full Auto Bolt Carrier Group
The Battle Arms Development AR-15 Enhanced Full Auto Bolt Carrier Group is another BCG capable of handling fully automatic fire. This bolt carrier group is built out of high quality 8620 steel and has a nitride finish that is very rust and corrosion resistant.
Built to mil-spec standards, meaning that it will be compatible with most other AR-15s out on the market, the Battle Arms has been CNC heat treated for added rust and corrosion resistant. The gas key is properly staked, and the entire group as a whole is magnetic particle inspected.
Another unique feature to the Battle Arms is the fact that the bolt carrier group is specifically shaped to reduce carrier tilt. This increases overall reliability since the key bearing surfaces are relocated.
All in all, the Battle Arms is a solid choice for a full auto bolt carrier group. Built to mil-spec standards with a durable 8620 steel construction and nitride finish, this bolt carrier group will be long lasting capable of lasting for several generations. It’s also been heat treated for added strength and comes magnetic particle inspected.
- Built out of high quality 8620 steel
- Firing pin comes with a hard chrome finish
- Gas key is properly staked
- Magnetic particle inspected
- Built to mil-spec standards
- Comes with a rust and corrosion resistant black nitride finish
- Heat treated for added strength
- Bolt carrier is specifically designed to reduce carrier tilt and improve reliability
- Quite expensive for bolt carrier group
And that concludes our list of the top three best bolt carrier groups for an AR-15 in 2021.
Any one of these bolt carrier groups that we have covered here today will be a solid choice for your AR-15, or alternatively, you can follow the buyer’s guide that we outlined and discussed above to help you find a solid pick as well.
Just remember that finding the highest quality bolt carrier group you can get is vitally important for ensuring the durability, longevity, and functionality of your AR rifle or carbine.