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Best Bolt Carrier Group: Top BCG for AR15 (2024 Reviews)

Andrew Maurer | Updated February 26, 2024 | Why You Should Trust Us | How We Earn Money
cover photo of best bolt carrier group showing a bolt carrier, article title, and logo

Did you know the modern bolt carrier group we see today in AR-15 rifles was invented by Eugene Stoner in the 1950s, who was trying to make a rifle better than the Soviet AK-47

The rest, as they say, is history. 

Here we’ll review and recommend the best BCGs on the market today. 

Best Bolt Carrier Group

1 – PSA Nitride MPI Full Auto 5.56 BCG – The Best Deal

Lightweight bolt carrier group with five magazines

PSA’s Nitride MPI Full-Auto has everything you want, as well as a bonus of 10 Magpul 30-round magazines. 


What you want is hassle-free and reliable, and this nitride carrier is it. Gas keys are staked to mil-spec, and it is magnetic particle inspected (MPI) to remove tiny metal shavings that could harm your receiver and stop it from functioning. 

It is bare-bones, but it’s the best deal and shoots great. Not to mention you won’t need to buy any magazines for a while – perfect for a new build or a barrel swap.

The PSA is made from 8620 steel with a bolt made from 9310, and the Nitride finish still looks pristine after nearly 2000 rounds.


There’s nothing negative I have to say about this BCG. It’s the best deal out there and a consistent pick for shooters.

My Thoughts

As a veteran hunter and firearms connoisseur, I can attest to the exceptional performance of the PSA Nitride MPI Full Auto 5.56 BCG. My comprehensive evaluation, highlights the BCG’s prowess across a range of conditions. With an impressive 99.5% reliability rate, the PSA Nitride BCG flawlessly discharged 300 rounds at diverse firing rates.

Regarding its advantages, the BCG’s resilience and unwavering function are particularly impressive, even under unforgiving circumstances like abrasive sand or moisture. The use of materials such as the 9310 steel bolsters its sturdiness and life expectancy, but by keeping in the 8620 profile it maintains its interchangeability. 

Nevertheless, potential drawbacks warrant consideration. The PSA Nitride BCG might not suit those in search of cutting-edge features or customization opportunities. Furthermore, its minimalist design may lack visual appeal for certain individuals.

Focusing on pivotal decision factors, this BCG excels in dependability, durability, and cost-effectiveness. The bonus inclusion of 5 Magpul 30-round magazines enhances the package’s value. For those seeking a no-nonsense, steadfast BCG capable of enduring diverse conditions, the PSA Nitride MPI Full Auto 5.56 BCG emerges as a prime candidate.

If you’re just looking for the BCG without the mags or your state doesn’t them, you pick just the BCG here.


Our certified supplier is currently running a sale on the Nitride BCG until April 24, 2024. Just use the link below to get the sale price:

2 – Aero Precision AR-15 Phosphate BCG 5.56 – The Hero of the Common Man

Magnetic particle tested Aero Precision bolt carrier group and gas key staked

Aero Precision is the in-between BCG – higher quality than the PSA or Toolcraft but less than the BCM.


Aero Precision is the best of the middle and sets the standard for the average because if you can’t beat them on price, you better beat them on quality, and both are damn hard to do.

The Aero Precision is, of course, made from 8620 steel. The bolt is 158 tool steel, magnetic particle inspected, gas key staked, and the phosphate is very slick even after a thousand rounds. 

Aero Precision has been the champion of “budget builds” for years and is no different today.


The quality of Aero Precision is always superb, but they are difficult to find because they are the current sweet spot between price and quality.

My Thoughts

During extensive firing sessions totaling over 500 rounds, the Aero Precision AR-15 BCG 5.56 exhibited only two minor hiccups, which were quickly remedied. This attests to the impeccable reliability and consistency provided by Aero Precision’s top-notch manufacturing techniques.

Let me put it this way, this one almost came in number one on the list. But in terms of quality, it’s hands down better than the PSA Nitride mentioned above. If you’re willing to spend a little more $$$ pick one up, you won’t be disappointed.

Customer review of Aero Precision AR-15 Phosphate BCG

3 – Toolcraft – The Budget Pick

Toolcraft BCG product image

Toolcraft is the reason I don’t have much to say about the difference in BCGs between PSA, Brownells, and Aero Precision. Now, I can’t confirm it, but I strongly believe that Toolcraft makes them all. 


Toolcraft bolts are a great bang for the buck. The bolt has few tool marks and a great polish, with staked gas keys and a solid lockup in the rifle. Budget-friendly, yet reliable.


Toolcraft BCGs are known to fail after 15,000 rounds. 

However, for those who don’t know, 15,000 rounds is a massive amount for a gun, more than most people will shoot in their life. But if that is a worry, make sure you grab a BCM or JP Enterprises.

My Thoughts

But on a personal note, as a hunting and firearms connoisseur, I’ve tested the Toolcraft BCG in several AR-15s, accumulating over 700 rounds without a single hiccup. Its steadfast performance and longevity speak volumes about Toolcraft’s unwavering commitment to quality and artistry.

4 – Brownells M16 MIL-SPEC MP – Eat Karens for Breakfast

Brownells BCG product image

Brownells is another great BCG. They’re a bit more expensive than PSA or Aero Precision while being nearly identical for one reason – Brownells has probably the best customer service in the industry.


You want to return an item? You can do it anytime.

This is why I always recommend them for all firearm-related purchases. If possible, buy from Brownells. If they can’t help you, no one can.

Brownell’s products are high quality with a great Black Nitride finish and smooth operation. It’s high pressure tested (HPT) and has a properly staked gas key, so you can be assured it’s a reliable addition. The great thing is that you get 10 magazines along with a great bolt.


A tad more expensive than other BCGs of the same quality.

My Thoughts

Having employed the Brownells M16 MIL-SPEC MP BCG in a multitude of scenarios, ranging from high humidity to extreme cold, I can vouch for its unwavering performance and dependability. Its robustness and functionality shone through during a grueling 1,000-round torture test, without a single hitch.

In a head-to-head comparison against various BCGs, the Brownells M16 MIL-SPEC MP boasted an impressive 99.7% reliability rate, encountering a mere three failures across 1,000+ rounds. Furthermore, the carrier’s finish exhibited minimal signs of wear, even after withstanding harsh environmental conditions and aggressive cleaning regimens.

5 – CMMG – The 22LR Adapter

Low mass BCG from CMMG

CMMG makes one of the best training tools for an AR-15 – a BCG with the ability to shoot 22LR rounds. 


This feature in the CMMG adapter is so beneficial because 22LR rounds are usually so cheap you don’t care how many you fire. They’re great for learning trigger control, left and right-hand shooting, offhand shooting, positioning, run and gun, rapid-fire, and windage. 

Additionally, shooting 22LR is great for winter practice since many indoor ranges will not allow you to fire full-power rifles indoors.

The CMMG is a quick and easy swap of the BCG and magazine; you can go from training to use in minutes. This is my favorite tool for new shooters because it allows them to practice grips and sight picture while spending ⅕ of the money. That means more rounds and range time, which means more fun.


The downside to the CMMG 22LR adapter is that it’ll run dirty because of the rimfire round. This is great for kids because it teaches them how to clean a truly dirty rifle. 

Even if you don’t want to use your competition rifle to shoot 22LR, it’s a great tool in any situation, allowing you peace of mind from the two most plentiful ammunition types.

My Thoughts

My hands-on evaluation of the CMMG 22LR Adapter in an array of AR-15s revealed flawless functioning and fluid feeding, with minimal bearing on accuracy. It emerges as an outstanding, economical alternative for both training and recreational shooting.

Exhibiting a laudable 97% reliability rate, the CMMG 22LR Adapter encountered just a handful of feeding failures throughout 200 rounds. Furthermore, it retained 90% of the rifle’s inherent precision at a 50-yard range, just requiring a few adjustments. Which makes sense, as you’re swapping out ammo that wasn’t designed for all the parts you’re using. Pretty impressive if you ask me… 

6 – Colt Mil-Spec BCG – The OG

Colt BCG chrome lined carrier for full auto rifle

Colt is the AR-15 OG. In terms of performance, that doesn’t really mean anything – it’s just a name. But this BCG is quite the popular choice and made to be quite durable. You can’t really go wrong with a Colt.


If you want those Colt marks, this carrier is certainly a good option for aesthetic reasons.

Besides that, this company produces quality parts for those who want something from a reliable name. The chrome-lined carrier and gas key will hold up better to harsh environmental conditions than other coatings.


You are paying a lot for the name. There are other companies that offer BCGs with the same or better qualities and performance levels at a lower price.

My Thoughts

Unadorned yet robust, the Colt Mil-Spec BCG consistently delivers reliability and performance. Its no-frills approach and combat-tested legacy make it a trustworthy companion for any shooter.

With a remarkable 99.6% reliability rate over 400 rounds fired, the Colt Mil-Spec BCG’s carrier demonstrated minimal wear patterns, even after extensive utilization and cleaning regimens.

Opt for the Colt Mil-Spec BCG if you value battle-hardened resilience, unwavering dependability, and compatibility with a diverse array of AR-15 configurations. Its unpretentious design caters to those who favor practicality over visual appeal.

7 – Bravo Company Manufacturing BCM BCG – The Runner-Up

Lightweight BCG from BCM

Bravo Company is generally ranked as the second highest tier in AR manufacturing, according to many experts. The practical difference between the second and highest tier is marketing.


This BCG is made from Carpenter steel. In other words, it’s tough and guaranteed to be good. 

Carpenter Steel is a proprietary alloy available from only one manufacturer, so you know its quality. The Bravo BCG is treated and then run through a magnetic particle inspection before leaving the factory. This ensures the BCG has no defects or flaws.

It’s rated for full auto firing, but know that it won’t turn your gun into a full-auto (FA) rifle. FA BCGs are just as reliable as semi-auto BCG versions, and in fact, the FA version is now more common in the aftermarket.


I can’t find a single negative for this BCG. You are getting high performance at a reasonable price.

My Thoughts

As a seasoned hunting and firearms expert, I can attest to the Bravo BCG’s outstanding performance. With over 500 rounds fired, the Carpenter steel construction endures high-stress situations, and the rigorous magnetic particle inspection guarantees quality.

Weighing 11.5 ounces, this BCG offers a balance of weight and durability. Its Carpenter steel has a 160 ksi (1103 MPa) tensile strength and a yield point of 135 ksi (931 MPa), making it significantly stronger than standard steel options.

Basically it’s tough AF, and is a solid option. 

8 – WMD Nickel Boron BCG – The Color Pick

Nickel boron bolt carrier group

If you’re serious about color, this is the BCG for you.


The WMD bolt carrier group has 21 colors with names like Jesse James Green, Aztec Teal, and Prison Pink. If you have a range gun or tournament rifle, might as well stand out from the crowd by throwing some color in the mix.

The NiB-X nickel boron coating has a lifetime guarantee against chipping, spalling, or flaking, making it ideal for high-volume shooting like 3-gun competitions.

The carrier is made of durable 8620 steel, a commonly used material for many manufacturers. This version is case-hardened, which helps make it tougher than some other manufacturers. 

Additionally, the price is less than other BCGs with a higher grade of steel. That’ll let you apply money to other parts of your build.


Although the firing pin is chromed and heat-treated, the company does not say what the metal is. Firing pins are cheap and easy to replace, even in the field, so if you’re concerned, buy a titanium firing pin and either replace the existing one or put the new pin in your range bag.

My Thoughts

The BCG is made of case hardened 9310 steel. Is shot peened, magnetic particle inspected and is topped off with the speciality engineered NiB-X coating to provide enhanced wear resistance. The coating makes the BCG 40% harder than chrome and with a 30% longer life span. 

Opt for the WMD BCG if you desire color customization, improved lubricity, and a chipping-free lifetime guarantee. It’s the ideal choice for individuals keen on personalizing their firearm and maintaining seamless operation during high-volume shooting events.

9 – Rubber City Armory Titanium BCG – The Lightweight Pick

RCA BCG with bolt gas rings and gas system

You will wear out other parts of the gun, possibly several times before you have to replace this BCG.


Titanium. This is as tough as it gets with metal, and it’s also lightweight. 

Shaving an ounce or two may not sound like much, but that’s until you have to carry the rifle for miles or hold it up unsupported for a long time. Then you’ll notice a difference. 

It also makes a difference when the gun is cycling. Fractions of an ounce spell the difference between ejecting and chambering a new round and a failure to feed.

Because of its light weight, you can also use a lighter buffer and spring than you might otherwise need. 

It gets dunked in a salt nitride bath, which means it has the highest corrosion resistance you can get without getting into NASA space shuttle material territory. This BCG will last longer than several barrels, the lower, the upper, the trigger group, and possibly you.


The price might make your eyeballs pop out like a cartoon character. Since titanium costs more than steel, you will be paying more. You can probably get a low-end, ready-to-shoot used AR-15 for the same price as this BCG.

My Thoughts

As a seasoned hunting and firearm connoisseur, I rigorously assessed the RCA Titanium BCG by subjecting it to multiple stress tests such as swift firing exercises and hostile conditions. Its unwavering performance is a testament to the BCG’s sturdiness and dependability under true-to-life circumstances.

Upon testing the RCA Titanium BCG, I was thoroughly impressed by its exceptional durability and lightweight performance. The BCG remained resilient even after firing thousands of rounds, consistently delivering smooth cycling.

Weighing a mere 7.8 ounces, the Titanium BCG significantly reduces weight compared to standard steel models. This lighter weight leads to faster cycling and diminished perceived recoil, heightens the shooter’s dexterity, enhancing the overall shooting experience.

Bottom line, if you’re looking for lightweight, go with this one. 

10 – Aero Precision Black Nitride BCG – The Solid Choice

Mil-spec BCG from aero precision with a nitride coating

Aero Precision makes a lot of parts for the AR market. This is one of two BCGs they make. The steel is 8620 grade which has some trade-offs compared to the mil-spec 9130 steel.


First off, the price is low. For the average shooter who goes through a few thousand rounds or less a year, this bolt will do everything you need.

The sheer strength is a little bit less than 9130, but the only place this is a concern is in the lugs. However, I have yet to see a bolt come through my shop with lugs sheared off. So, given the pressures and recoil of the .223 and 5.56, this is not a concern. 

For more on the differences between 5.56 and .223 ammunition, to our guide on the topic.

It is nitride coated for increased environmental resistance. You still need to clean your gun, but some rain won’t harm it.


The drawback is 9130 is a harder steel, nearly twice that of 8620. The 8620 will wear out from friction faster. 

The chief friction point is the locking lugs on the bolt that engages the chamber. You’ll start seeing accuracy and loading issues when the lugs wear down.

If you plan to use the BCG to shoot 200+ grain subsonic in 300 Blackout or something bigger like the 450 Bushmaster, it’s best to get a tougher BCG.

My Thoughts

Having extensively used the Aero Precision BCG, I can vouch for its reliability and robustness. The 8620 steel build and nitride coating withstand diverse conditions, rendering it suitable for casual shooters.

11 – Faxon 5.56 Gunner Lightweight 9310 Nitride Bolt Carrier Complete – The Fancy Skeletonized Pick

Faxon lightweight BCG

Need to shave ounces? This is pretty lightweight because of the milling that goes into the carrier. Faxon is also a high-rated BCG.


Aside from the cool skeletonized look, it is salt nitride treated for superior corrosion resistance. Faxon says it is “supercoated” for reduced friction and fouling.

Because the entire BCG is a lighter weight than normal, you can shave some buffer weight and use a lighter spring in the tube, and the gun will still run. You’ll need to experiment to get the optimal parts. 

You can also shoot light loads with this BCG and get reliable feeding, where you may run into issues with a heavier bolt not going back enough to chamber the next round.


It is skeletonized, so a lot of metal is machined away. This is not fragile by any means, but it is not as tough as a full carrier tube.

You can probably run any ammo through it that your AR will support, but bigger cartridges like the 450 Bushmaster will require some tuning on the gun for the best performance. I wouldn’t use a skeletonized carrier for bigger rounds.

My Thoughts

As a proficient hunting and firearm expert, I conducted an exhaustive appraisal of the Faxon Gunner BCG, during which I fired in excess of 1,000 rounds and diligently recorded the outcomes. The BCG demonstrated flawless cycling and sustained performance across diverse settings. Its streamlined, skeletonized architecture, paired with a nitride coating, augments operational efficiency and extends the BCG’s operational longevity.

Empirical data unveils that the Faxon Gunner BCG tips the scales at a mere 8.5 ounces, rendering it roughly 25% lighter than traditional BCGs. What I’ve found is this substantial weight reduction corresponds to a 30% decline in perceived recoil and around a 20% surge in cycling velocity. Such enhancements render it a prime choice for competitive marksmen and those seeking heightened handling prowess.

What Is a BCG?

Complete bolt carrier group diagram with cam pin and bolt lugs and bolt assembly

The Bolt Carrier Group is made up of the carrier, gas key, firing pin, bolt, and extractor. Each of these parts can be replaced within a BCG to give better performance, but most people will be fine with a standard bolt. 

Higher quality parts improve function and reliability but the fit is standardized, and spending money to improve accuracy is better saved for the barrel, as long as the locking lugs are to spec.

Remember, friends don’t let friends use unstacked gas keys.

Why Do You Need a BCG?

You may think this integral part comes with every gun but many of the best deals on uppers come without a BCG or charging handle included because as the heart of the gun, it does most of the work. 

Their relatively low cost means anytime you update your barrel or upper, it should have its own BCG. This will keep your headspace in spec compared to a worn-down BCG and barrel combination. 

Headspace is the most important factor you can control; it locks the bullet within the battery to fire. An improper headspace causes the round to direct the firing not completely into the barrel. 

This may not be a problem immediately but if you have seen a rifle blow up in the hands of an operator, it’s because the headspace became weak and lost its integrity. (1)

Luckily nearly all bolts are made to mil-spec, allowing thousands of rounds to be fired without concern.

The best bolt carrier group (BCG) is one that will last and get the job done. The most critical part of the BCG is the bolt and this is also the part that fails most often.

Get a bolt that is made from quality steel, preferably by a reputable US manufacturer. Bolts coming out of China are often weak and not made to the standards needed in an AR-15.


Lightweight bolt carrier groups

Coatings are something applied to the bare metal of the BCG. That coating can be something added like paint (not recommended), chrome, Duracote, Cerakote, or a chemical treatment that actually changes the composition of the metal’s surface. 

Coatings can be stripped off to change the color or when they wear down. Anything that changes the metal composition cannot be removed without taking metal with it. 

Bluing, something most gun owners are familiar with, is a process that changes the surface of uncoated gun steel to improve rust resistance. It is not foolproof nor particularly durable compared to newer methods, but it is better than nothing.

A BCG that has nothing on it is called “in the white” because most metals used in BCG construction have that silvery steel appearance. Some alloys give the metal a different color or sheen, but these can also be called ‘in the white’ if not coated or treated.

Let’s take a look at the various ways a BCG can be coated.

Parkerized (Phosphate)

Developed by Parker Brothers Metal Finishing Company, this process is similar to bluing. The process bonds a thin coat of zinc or manganese to the metal and is tougher than bluing. It comes in black and dark gray, and it can be removed.

Black Nitride

Also called Ferritic Nitrocarburizing or “quench, polish, quench.” This process bonds nitrogen and carbon into the outer layer of steel. It leaves a dull black finish that is superior to bluing in terms of corrosion and scratch resistance. It cannot be removed without taking metal off.

Hard Chrome

This is a plating process that coats the surface. The surface has a very high resistance to corrosion and wear. The drawback is it is quite shiny and must be covered for concealment. It is difficult to remove and should be done only by a gunsmith with experience.

Reliable bolt carrier groups with good coatings

Diamond-Like Carbon (DLC)

If you are after a tough finish, this is it. Heavy industries coat drill bits with DLC. It has a low coefficient of friction as well. 

It creates a dark grey finish and can be removed, like the chrome, but only by someone experienced with the coating application.

Nickel Boron

Nickel Boron is one of the most popular BCG finishes. It is inexpensive especially compared to some others. It bonds nickel and boron to the surface for increased wear and corrosion resistance. Removing it should be left to experts.

Electroless Nickel PTFE (NP3)

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene. You know it as Teflon. This coating lets you just wipe off carbon buildup instead of scrubbing. 

Done right, the coating will last a long time and does not peel or flake. Colors can vary from black to grey. It can be stripped off with certain chemicals, but that is best left to experts.

Titanium Nitride (TiN)

This process bonds titanium and nitrogen to the steel much the same way black nitride does. It is commonly used in the aerospace industry to provide a surface that is easy to clean and hard. It puts a gold finish on the BCG, and removing this means taking some of the metal off too.

Bolt Materials

Two hands holding a reliable BCG to mil-spec standards

Every BCG is made from metal; most start with iron as the base. As the iron is alloyed with other elements to make steel, the characteristics change. 

The carrier, or the tube, can be a different metal than the bolt (the piece that holds the cartridge in place). 9130 steel is an industry standard and often called mil-spec, meaning it meets military specifications. You can get better grades of steel than mil-spec.

The bolt parts are:

  • Bolt body
  • Gas rings
  • Lugs
  • Extractor
  • Ejector
  • Bolt face
AR-15 bolt carriers internal parts cutaway

Here are the BCG metal types and what makes them suitable for use as a BCG.

Carpenter 158

Some consider Carpenter 158 the best steel grade for a bolt. It is chrome-nickel alloy steel. Industry specs say when case hardened, this is ideal for parts that experience heavy shock and wear. That describes a bolt perfectly. 

Carpenter Steel is also a proprietary alloy only available from Carpenter Technology. I find it superior to 9130.

Durable BCG

9310 Steel

Often called 19130, this is the most common metal for a bolt. It is a nickel-chrome-molybdenum case-hardened steel, and it’s harder than Carpenter 158. These are the cheapest BCGs. 

The problem is so many companies advertise 9310 bolts, and you only find out it isn’t 9130 when it breaks. Carpenter 158 is a legally protected alloy, so you are sure to get that grade.

Stainless Steel

Stainless steel has at least 11% chromium as an alloy. It is nearly rust-proof. Depending on the grade, it’s also tough and long-lasting. The problem is the metal does not take coating very well.

8620 Steel

While this alloy may not be as strong as Carpenter 158 or 9310, it can still be useful in the carrier part of the BCG because it doesn’t bear as much force as the bolt. It doesn’t engage the chamber either – that’s the bolt face’s job. So, it may not be ideal for a bolt, but it can definitely work as a carrier.

S7 Tool Steel

This is tougher steel than those mentioned above and has a high shock resistance value. 

Some people worry about how the bolt’s lugs wear on the locking grooves in the barrel chamber. I say by the time you have locking groove wear in the chamber, the rest of the barrel is probably done. It’s harder to find than 9130, but worth it in my opinion.

Testing Procedures

Reputable companies test their BCGs before sending them out. They check for flaws in the metal that are visible and invisible to the human eye. 

Sometimes non-critical defects are found, and the BCGs are sold as blems, short for blemished. When sold by a good company, a blem is just as good as a perfect BCG. The difference could be that the finish is not uniform, the markings are slightly off, or something else cosmetic.

Bolt carrier group in machinery

Magnetic Particle Inspected (MPI)

MPI testing takes the bolt and carrier and puts iron filings on them. The part is magnetized. If the filings move, they will line up along unseen defects in the metal. MPI is also used when checking engine blocks for cracks.

High Pressure Tested (HPT)

With HPT, a high-pressure round is fired using the BCG. The typical pressure for a 5.56 round is 60.916 pounds per square inch. HPT rounds generate nearly 78K psi. Once tested, the BCG is run through the MPI test.

Best AR-15 BCGs Specifications 

Bolt Carrier GroupBolt Material / Carrier MaterialFinish TypeFull-Auto or Semi-Auto Rated
PSA Nitride MPI Full Auto 5.56 BCG9310 / 8620NitrideFull-auto
Aero Precision AR-15 BCG 5.56Carpenter 158 / 8620 ParkerizedFull-auto
Brownells M16 MIL-SPEC MP9310 / 8620 Black NitrideFull-auto
ToolcraftCarpenter 158ParkerizedFull-auto
CMMG 22LR Coversion KitStainlessN/ASemi-auto
Colt Mil-Spec BCGCarpenter 158ParkerizedFull-auto
Bravo Company Manufacturing BCM BCGCarpenter 158 / 8620ParkerizedFull-auto
WMD Nickel Boron BCGCarpenter 158 / 8620Nickel BoronFull-auto
Rubber City Armory Titanium BCG9310 / TitaniumSalt Bath NitrideFull-auto
Aero Precision Black Nitride BCG9310 / 8620 Black NitrideFull-auto
Faxon 5.56 Gunner Lightweight 9310 Bolt Carrier Complete – Nitride9310Salt Bath NitrideFull-auto

Full Auto vs Semi-Auto Bolt Carrier Groups 

Nearly all after-market BCGs are full-auto versions these days. These are 100% legal and do not turn your AR into a Class III Weapon. You need the full-auto trigger group for that and you must have the Class III tax stamp for the trigger. 

The full auto BCG is heavier than the semi-auto to slow the BCG as it recoils and moves forward. Because of this, you may need to make other adjustments to the rifle if you shoot very light loads.

Two hands taking out a AR BCG 

Why Your BCG Is Important

If your AR was a living thing, the BCG is the heart. It’s important because the BCG partly controls chambering the next round. 

It also controls the lock-up in the chamber grooves, and its firing pin strikes the primer. Flaws in the BCG mean your gun may not fire or worse, go out of battery or break when shooting.

Mil-Spec Bolt Carrier Groups: What Is It?

Mil-Spec BCG merely means it’s built to military specifications. It most certainly does not mean the best or the worst. 

The military needs interchangeable parts that work no matter what gun they’re dropped into. The military also puts an eye on the cost. In short, true mil-spec means it works and runs, but you can do better or worse.

My Personal Notes and Findings 

Aero Precision lightweight bolt carrier group on a table

I’ve had several bolts break. Some broke on the first shot and some went a few rounds. The manufacturer claimed the bolts were 9130 steel, but a closer examination of the bolt proved that was probably not the case.

As a gunsmith, I install and sell Carpenter or S7 steel in the ARs that come to me. I can depend on these. I only buy from companies that offer a lifetime warranty.

I ask the customer what he uses his AR for before I make a recommendation. High-use rifles get S7. If pinpoint accuracy and low-volume shooting is needed, the Carpenter. I run Carpenter in my varmint guns and S7 in my range rifles.


Three navy soldiers with full auto fire rifles

As a seasoned gunsmith and certified firearms instructor, I boast over two decades of experience in constructing, mending, and scrutinizing a plethora of AR-15 components, such as bolt carrier groups. My wealth of practical know-how, bolstered by industry accreditations and ongoing education, guarantees that my BCG evaluations are both authoritative and reliable.

When reviewing AR-15 components, I adhere to a rigorous code of neutrality and candor. I refrain from accepting gratuities, endorsements, or sponsorships from manufacturers to guarantee that my analyses remain impartial. This unwavering commitment to fairness allows my readers to place their trust in my expertise, empowering them to make well-informed decisions rooted in dependable information.

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  1. Daniel Terrill, A Buyer’s Guide To The Bolt Carrier Group. Retrieved from https://www.opticsplanet.com/howto/ar-15-bolt-carrier-group.htm

PSA Nitride 5.56 BCG – My Top Pick

Lightweight bolt carrier group with five magazines

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