So you decided to build a semi-automatic rifle with the proper upper receiver. Choosing the right bolt carrier group for your AR-15 or your M16 semi-automatic rifles can be frustrating, seeing all the really cool options.
Regardless of whether you want to build a new AR-15 from scratch, or just want a simple upgrade, the bolt carrier group definitely needs a little bit of digging and researching relevant info.
A lot of the ones you see on the internet could seem like the right choice for your semi-automatic rifle, and to be honest, you won’t be wrong if you go for an Aero Precision, Toolcraft, Bravo Company, Spike’s Tactical, or the WDM Guns models. All of them really just get the job done.
But, the price range, characteristics, qualities, and those tiny details can really make a difference, along with this guide, will help you really narrow down the vast options that are available today.
In this BGC buyer’s guide, we’ll talk about the essential features, finishes and coatings, materials, full-auto or lightweight types, and other important factors to consider when choosing the best bolt carrier group.
You’ve probably seen those Mil-Spec (military specifications) details and you’re probably even more confused or you’re having second thoughts about upgrading your upper receiver.
Don’t worry. We’ll keep it simple and I won’t bore you with the sciences. I’ll just list the best materials, coatings and finishes, and types to consider while highlighting their characteristics.
What’s a Bolt Carrier Group and How Does It Work?
A bolt carrier group isn’t the most important part of an AR, but it might as well be.
It’s basically the heart and soul of a semi-automatic rifle, and before we start to blatantly humanize weapons, let’s just go over the details.
Simply put, the BCG’s duty is gas-operated and performs firing functions like striking the firing pin, using gas via fired rounds to push the recoil spring back, ejecting the fired rounds, chambering a new round from the mag, and re-cocking the hammer in one cycle.
It’s gas-operated and redirects the gas directly into the chamber which ejects the cartridges and cycles new rounds.
Some ARs like the AK-47 use a gas-piston system that pushes pistons to function, and these are generally regarded as slightly more reliable.
What Are the Components of the BCG?
The BCG consists of the carrier, bolt, gas key, firing pin, and cam pin.
- The Bolt Carrier houses the bolt and is attached to the gas key and is in direct contact with the spring and the buffer. Once fired, it travels back from the force, and enables the fired shell to be extracted and reloads a new round. It requires regular cleaning to function properly.
- The Bolt Gas Rings traps the gas from the fired round.
- The Bolt and Extractor guide rounds into the chamber, extract spent casings, and eject the cartridges once fired.
- The Gas Key, or the ‘bolt carrier key’, funnels the gas from the gas tube and into the bolt carrier. It needs to be tightened at all times and staked to create a seal in order to keep the screws on.
- The Firing Pin strikes the primer, igniting the cartridge, causing a small explosion, and propelling the projectile via gas.
- The Cam Pin keeps the bolt inside the bolt carrier in a straight line and locks it into position into battery. ‘Into battery’ is a fancy way of saying ready to fire.
There’s no doubt that it’s an essential component of your AR-15’s upper receiver because the operations we mentioned above are usually a deciding factor for your AR-15’s reliability.
The BCG functions with the buffer, tube, and buffer spring to cycle the operations, and depending on the quality, it affects firing, cycling, recoil, muzzle rise, and overall shooting experience.
Why Do I Need to Upgrade My Bolt Carrier Group?
A brand new one offers durability, withstands a lot of heat, improves reliability, and shortens the reloading and cycling time.
Getting a new one is unnecessary if your semi-automatic rifle is brand new if you ask me.
If it isn’t broken, don’t fix it.
Of course, if you like to speed things up with the cycling operation or handling, then by all means, go for a new BCG. For example, a 9310 steel model is heavy-duty, reserved for those who regularly visit the firing ranges and unload a lot of bullets in a short time span.
We’ll discuss the characteristics in the buyer’s guide section below.
I first suggest you diagnose the whole thing, check your ammo, barrel, or magazine, before deciding to get a new BCG, because, let’s be frank here, they aren’t exactly cheap.
So, without further ado, let’s check out one of the most effective, reliable, lightweight, and affordable BCGs with great value you can find on the market today.
Best Bolt Carrier Groups
- Shrouded firing pin
- Magnetic particle inspected and shot-peened for durability and longevity
- Nickel boron finish is easy to clean and offers wear-resistance
- Impressive heat resistance
- Easy to install
- Besides bolt discoloration after prolonged shooting periods, there aren’t many downsides
Here’s the WMD Guns M16 5.56 NATO Nickel Boron BCG.
The manufacturer is well-known for their standard lines with solid coating technologies and materials which offer top-notch reliability in the upper receivers industry, and they have this BCG to prove it.
It’s made from a stable mix of nickel and boron, comes with a staked gas key, shrouded firing pin, full-forward assist teeth, and a classic M16 design. Thanks to the nickel boron finish, it’s easy to clean, doesn’t allow carbon to stick, and offers smooth operations.
The nickel boron (NiB) finishes used to be a lot more expensive, but have since been lowered to an acceptable price point.
It’s magnetic-particle-inspected and shot-peened for increased longevity and reliability, and the bolt is heat-treated with a Carpenter 158 steel, while the carrier is 8620 steel, heat-treated and case-hardened. Although, there are some models whose bolt is made of 9310 steel.
The carrier offers superb handling and doesn’t wear off easily, in contrast to other mil-spec coating types. It uses the M16 full-auto carrier and is suitable with a semi-auto AR-15 or an M4. It’s available with or without a hammer.
The WMD can withstand heat for a long time, but I recommend not overdoing it because it might get discolored.
For a model with hardened steel alloys, it’s pretty lightweight and easy to install.
I recommend this one for competitive shooters who like to shoot semi-auto bursts for a prolonged period of time.
- Ejector and extractor included
- Mil-Spec features
- Very durable
- Easy to install
- Shot-peened bolt
- Internal chrome-lined bolt carrier
- High pressure-tested and magnetic particle-inspected
- Friction and scratches may appear after test firing
- Low-quality parkerized finish
- Not affordable and may be difficult to find
Bravo Company Manufacturing (BCM) is a solid manufacturer with a reputation for having mil-spec products in the upper receiver business. Each of their bolt carrier groups is carefully tested before shipping.
Bravo Company are also known for their high-end semi-automatic rifles, and each of them is built with high-quality materials and is rigorously tested before shipment.
The BCM may be on the more expensive side, but it has outstanding quality and longevity. Additionally, it’s pretty easy to install, as it comes fully assembled and you only need to set it up.
It exceeds Mil-spec standards by a wide margin, and the bolt is made from Carpenter 158 steel, while the extractor and ejector are made from tool steel which offer excellent durability and reliability. The construction is both HPT (high pressure tested) and MPI (magnetic particle inspected). It comes with 8 hardened steel fasteners.
The parkerized finish might not withstand some test firing, but the chrome-lined internal parts offer smooth operation and cycling. You can check out the CMMG .22LR Bravo Conversion Kit if you’re looking to lower the bar to the more economic .22LR, and it’s very easy to install.
THE BCM is perfect for AR-15, M16, and M4 rifles, and can withstand long hours at the shooting range.
- High-quality titanium and steel construction
- Improved wear and reduced friction with polymeric absorption
- Increased lubricity and easy to clean
- Proprietary aerospace coating preserves titanium parts
- Tunable gas system
- May need an adjustable gas system
Rubber City Armory has always been a high-end brand and for a good reason.
They incorporate superb technologies like molecular realignment, special thermal processes, polymeric absorption, and black nitride coating for sturdiness, friction reduction, improving wear resistance, corrosion resistance, lubricity, and durability.
The RCA is a lightweight BCG with black nitride coating for that extra wear and corrosion resistance. It retains durability and longevity, and the special material and finish cut back on resources, making it a fairly lightweight BCG with only 7.8 ounces.
The bolt carrier is made of titanium, the bolt is of 9310 steel, and the cam pin and extractor are tool steel. It’s great for competitions and target practice and is best suited for long firing rates.
The downside is that if you’re looking to increase reliability, you have to tune your gas system.
If you’re going for a lightweight model with AR-15 compatibility, and you have extra cash, the RCA is your best bet.
- Gold titanium-nitride finish
- Reduced friction
- Solid corrosion resistance
- Highly durable
- High-quality 8620 and 9310 tool steel
- Heat-treated bolt carrier
- Low-quality control process
- Heavy (12 ounces)
There’s no complete BCG list without a Brownells Titanium Nickel bolt carrier group.
The Brownells TiN M16 Bolt Carrier Group offers durability, reduced recoil, and ease of maintenance with the gold titanium-nitride finish used on the carrier and bolt.
The carrier is 8620 tool steel, while the bolt head is 9310 tool steel. The bolt is MPI for extra reliability and the carrier is heat-treated for durability. It’s great for 5.56 NATO, .204 Ruger AR-15s, .223 Rem., and .300 Blackout calibers.
The titanium finish offers nice corrosion resistance and low friction, and the steel is HPT-tested for longevity. Simply put, it’s a great option for full-auto operation and prolonged use at the firing ranges.
An M16 carrier notch is included, for added reliability for full-auto semi-automatic rifles.
If you’re looking for a budget option, you can check out the MPI and mil-spec Brownells Nitride M16 BCG with a Nitride finish which makes it smooth and easier to clean. The bolt is made of 9310 steel instead of the lighter Carpenter 158.
- Easy to install
- High-quality stainless steel bolt carrier
- High durability, wear resistance, and reliability
- Great for .223 calibers
- Well-staked pins
- Affordable option
- Not very good outside competitive shooting
- Does not have a forward assist extension
Last, but not least, here’s JP Enterprises.
It’s a lightweight bolt carrier group and it can take a beating, all thanks to the 416 stainless steel – even though it’s a low-end BCG, it doesn’t wear easily.
It has a staked carrier key and a dust-guard notch, guaranteed to prevent any excess buildup which makes it easy to clean. A very accurate and well-designed, the rear of the bolt carrier functions like a semi-auto AR-15 configuration with an extended mi-spec cocking pad.
The finish is smooth, has high lubricity, and is easy to wipe down all thanks to its QPQ five-step process that renders the finish highly wear-resistant.
Although it’s easy to install, it’s not very suitable for the newbie shooter who had just built his Ruger AR-15. The expanded outer bearing surfaces ensure that it always correctly aligns with the upper receiver, and it also does a great job lowering recoil.
Keep in mind that lightweight BCGs have a lower reciprocating mass in contrast to other mil-spec types. This means that it needs an adjustable gas block to lower the gas channeling, as well as lower the recoil.
It’s missing a forward assist extension, but this won’t be much of a problem if you’re looking for a competition shooting type.
For a great price, the JP Enterprises Low Mass BCG is a lightweight budget option that offers smooth operations, lowered recoil, and increased reliability, and it makes sure your rifle serves you for a long time.
Here are some honorable BCG mentions that are also great if you’re looking for something more specific for your rifle.
- Corrosion-resistant nitride finish
- Hardened gas key via USGI specifications
- Not for right-handed rifles
Toolcraft are perhaps one of the best in the business. Their products are literally everywhere, and you won’t go wrong if you pick an M16 one from them.
The Toolcraft is a MP inspected, mil-spec beast, made of 9310 steel with a corrosion-resistant nitride finish for increased durability for a full-auto rifle, and can withstand heat and stress easily.
It’s a full-auto model, so you won’t have to worry about its longevity during practices at the firing range. It’s strong enough to handle full auto fire but it can just as easily be used for semi-auto rifles as well.
If you’re looking for left-handed AR-15s, check out our buyer’s guide here.
- Mil-spec characteristics
- Durable and reliable
- Shot peened
- HPT/MPI tested
- Properly staked key
- Forward assist serrations for easy operation
- Easy to clean
- Hard to find
Last, but by no means least, I present to you the Aero Precision 5.56 Complete with a phosphate finish.
Aero Precision are well-known for their rifle parts and uppers, and this one is a full mil-spec, guaranteed to make your rifle sing without hiccups for a very long time.
You can easily combine it with their other products, and they usually work well with each other, unless you’re going for a different finish. I recommend you check out their 5.56 nickel boron BCG if you’re going for something with a shrouded pin.
The bolt is made of Carpenter 158 tool steel, and the carrier is 8620 steel.
It weighs 11 ounces, and the carrier has forward assist serrations for easier handling and smooth operation. Additionally, it has an o-ring insert on its extractor which ensures the cycling functions properly.
What’s best about this one is the mil-spec characteristics like the phosphate coating, and the properly staked and chrome-lined gas key and bolt channel.
These are becoming hard to find, but if you happen to find one in stock, then I strongly suggest you go for the Aero Precision quality.
Let’s take a look at the construction types, finishes, materials, and some of the most important features.
Types of BCGs
Bolt carrier groups can be basically divided into:
- M16 – The heaviest of the bunch, M16 BCGs have a longer rear section and the extra mass offers longevity and durability. They are specifically made to take a beating and have excellent heat resistance.
- AR-15 – Very similar to M16 bolt carrier groups, they are designed for semi-automatic operation and they usually cycle much faster.
- Lightweight or low mass – they are the lightest option, great for competition shooting. It doesn’t necessarily mean that they have lower durability or longevity, but they need to be constantly fine-tuned to function properly.
There are also half-circle bolt carriers, in which a small part of the cylinder and the area behind the firing pin is milled off, creating a semi-circle. They are a lighter option, but they also require a lot of tuning.
What to Look For in Bolt Carrier Groups
Let’s say that mil-spec BDCs are a standard, and just keep it that way.
The reason why most gun owners go for mil-spec BCGs is that they are rigorously tested to pass military evaluation and see if they can withstand cracks and avoid reliability problems.
Let’s check out the basic mil-spec characteristics:
- High pressure tested (HPT)
- Heat-treated & shot-peened
- Magnetic particle inspected (MPI)
- Grade 8 fasteners
- Made of 8620 steel, and Carpenter 158 steel bolt
- Anti-corrosion, chrome-plated interiors
- Torqued and staked gas key screws
- Parkerized or phosphate finish that holds oil well
These are the crucial mil-spec features you should keep in mind if you’re looking for a reliable, high-endurance BCG.
Shrouded Firing Pin
Not all bolt carrier groups have a shrouded firing pin.
A shrouded firing pin, in contrast to the ‘beveled’ or unshrouded firing pin, greatly lowers stress and vibration and makes sure the gun won’t jam.
Besides looking for mil-spec characteristics, I recommend you always go for a product with a shrouded firing pin.
Materials and Construction
Almost every BCG is machined from 8620 steel, except for the Carpenter 158, which is usually used for carriers, and 416 stainless steel for the lightweight, low mass groups.
8620 steel is a durable alloy, but it’s not strong enough to make up the bolt, and this is where 9310 Steel comes in.
It’s a brilliant alloy with a hard core and decent fatigue strength, and it’s stronger than C158 and 8620 steel.
When it comes to materials, 9310, 8620, and Carpenter 158 steel really just get the job done and there are no special preferences.
The same goes for 6AI-4V Grade 5 titanium bolt carrier groups, which offer unmatched durability, lowered recoil, wear resistance, and a lightweight feel, but the problem is they are more expensive.
The only material to steer clear of is aluminum. They are lighter but they wear off easily and nobody wants to damage their guns in case of jams or cycling problems.
Coatings & Finishes
Parkerized Manganese Phosphate
The first finish/coating we’ll mention is parkerized manganese phosphate, as a mil-spec finish.
It resists corrosion, withstands high amounts of stress and vibration, is heat resistant, and holds oil well. Unlike other finishes like nitride, diamond-like carbon DLC, or titanium nitride, properly made BCGs with this kind of finish have a chrome lining inside their gas key and carrier.
It’s far superior to nickel boron coatings because it tends to coat the surface well and add to the durability and wear resistance. Additionally, it reduces friction well between moving parts.
Nickel Boron (NiB)
Then you have nickel boron (NiB) finishes which are very durable and smooth and have a low-friction characteristic which makes them very easy to clean.
A NiB BCG will serve your rifle a long time, but it also costs extra.
Chrome, as one of the most expensive finishes, offers superior durability. Chrome is a winner too, but it’s really hard to find, and there’s absolutely no need to burn more than 300$ on a BCG if you ask me.
Nitride is another popular finish and lining, and protects against corrosion, has decent heat resistance, but tends to chip and wear easily. It’s still a better alternative to chrome because nitride has special properties that change the molecular structure of the steel alloy and increase durability.
Lastly, titanium nitride is a name that’s thrown a lot, and for a good reason.
It’s one of the hardest ceramic materials that are oftentimes used in all kinds of aerospace and military devices and weaponry.
It offers unmatched lubricity, durability, and corrosion resistance.
It’s a mid-range tier, but rifle owners like this one better than the rest because of its recognizable gold color which goes well with the matte black components of a BCG.
What’s the Difference Between AR-15 and M16 Bolt Carrier Groups?
The main difference between an AR-15 and an M16 is that the M16 lower receiver has three trigger pin holes for the auto sear and can be milled to contrasted dimensions to suit full-auto firing.
AR-15 lowers don’t have a third trigger pinhole, and are suited for semi-automatic fire control groups.
M16 types are heavier than AR-15 ones, but it’s hard to notice.
Will Adding an M16 BCG to an AR-15 Make It Full-Auto?
Both AR-15 and M16 bolt carrier groups are compatible with each other. However, installing an M16 BCG on an AR-15 won’t make it fully automatic. They are just designed as a convenient industry standard.
Bear in mind that full-autos are slightly longer than semi-auto BCGs, and they have a lug that pressures to the sear of a full-auto AR, which allows bust or full-auto fire. Depending on the upper receiver, having a compatible one allows reducing recoil.
Additionally, if you have trouble with muzzle rise, you can check out our list of the best AR-15 muzzle brakes.
Should I Go for an AR-15 or an M16 Bolt Carrier Group?
AR-15 BCGs are considered to be lighter in weight, but there’s really not much of a difference.
I recommend considering nitride finishes, black nitride finishes, or nickel boron for smooth handling. For materials, you should look for titanium constructions for low recoil, and 9310 steel, if you’re going for added durability. Both are fine choices.
Remember that M16 BCGs are not regulated by the ATF and are fully legal. It’s not illegal to install an M16 in a semi-auto AR-15.
To sum up, fine-tuning your rifle with an upgraded BCG doesn’t have to be complicated. I’ve yet to see a really bad review. They all just seem to work fine.
If you’re having trouble with cycling, operation speed, or reliability issues, first check every other part of the rifle before upgrading your upper receiver and concluding to buy a new bolt carrier group.
There’s not much difference in handling and performance when going for either semi-auto or full-auto. Fine-tuning your rifle is recommended if you’re going for fine steel like 9310, 8620, or Carpenter 158 steel, just make sure it’s MPI (magnetic particle tested)
Finishes and coatings can be subjective and almost redundant, but they still have a say in reliability and smooth handling. Go for phosphate or hard chrome if you’re on a budget, but I strongly suggest nickel boron.
Choosing a heavy or a lightweight model is also entirely up to your preference, but I recommend heavier for prolonged reliability.
You can go for either Carpenter 158 steel or quality titanium machinery for your AR-15 or M16, and be sure to consider thoroughly stress-tested, shot-peened, properly staked, and the ones that went through rigorous magnetic particle inspection. They offer unmatched reliability and ease of operation.
I hope that this guide at least narrowed down your choices and cleared up some questions regarding the materials, finishes, and machinery-related factors.