A bolt carrier group (short form: BCG) is the basic functioning part of an AR-15 rifle. Proper choice range of a good BCG can mean the difference in calamitous situations. There are a heck lot of aspects that come into factor when choosing a BCG for your rifle. The BCG is unavoidably the most important and multifaceted part of an AR-15 rifle.
To help even out things, we will discuss here the characteristics of an ideal BCG bolt carrier group. You will also get to learn about some of the best BCGs that are currently available on the market to help you make your purchasing decision. So let’s get about it!
There are few parts of an AR rifle that are as significant as the bolt carrier groups. Although the standard Mil-Spec bolt carrier does its job well and has for many years, new developments in technology and materials have come along and transformed the design.
When you are looking at the Best Bolt Carrier Group to use for any AR 15, there are a number of influences you will have to consider. Like many aftermarket or post-purchasing pieces for ARs, a lot still depends on what the intended purpose of your weapon is, what sort of budget and price point you have to work with, firing frequency, and of course the rifle’s aesthetic pleasantness. On the other point, before we dive into the finer points of the best AR 15 bolt carrier group for your rifles, let’s first understand what a bolt carrier group is and what sorts of duties it performs.
Definition & Purpose : AR-15 Bolt Carrier Group
The physical best bolt carrier groups itself comes with and includes the bolt, gas key, firing pin, extractor, and cam pin. This unit, in its entirety hides inside the upper receiver. Its main purpose is to strip a round from the magazine, slot it, cycle the “action”, expel the empty brass, and then reset the hammer all in one single cycle. The best bolt carrier group (BCG) is easily the most important component of the weapon and has a large part in decision-making whether a gun is reliable or not. It truly is the core and soul of the weapon.
The best AR-15 BCG, when working with other parts of the gun such as the buffer, buffer spring, and tube, it creates the necessary motion to cycle the action as well as determine the degree of muzzle rise and recoil as any shooters will experience when using.
It is a known fact that BCG is a short form for the bolt carrier group. It is found located between the upper and lower receiver of an AR-15 and performs all the basic purposes of the rifle. The function of the BCG is to hammer (open fire) around, load a new round, and eject the used cartridge, all that by itself. A bolt carrier group (BCG) contains six different components respectively:
- Retaining Pin
- Bolt Cam Pin
- Gas Key
- Bolt Assembly
- Firing Pin
The direct gas impingement system of an AR 15 made use of the gas released after firing a bullet to transfer the bolt carrier group backward and forward to achieve the three functions – cycling, ejection, and reloading.
The bolt carrier group (BCG) offers the AR-15 semi-auto firing capabilities, which means that you can fire rounds successively without having the need for pulling the charging handle after single every shot. A bolt carrier group (BCG) is the part that makes the AR 15 semi-automatic and the most sought after rifle.
The Different Kinds of Bolt Carrier Group (BCG)
Generally, bolt carrier groups come in several different options. However, there are 3 main bolt carrier groups available: M16 bolt carrier, AR 15, and lightweight. Both the M16 and AR-15 share many of the same aspects, however, each has its own resolution and function.
The M16 bolt carrier version is much heavier and has a long, full-size rear section compared to other bolt carrier groups (BCG). The amplified mass remains in the battery longer and is made to withstand the exploitation of full-auto fire as well as match grade guns. The AR-15 BCG on the other hand is designed for semi-auto fire and cycles faster, usually mostly due to its lighter weight.
Last but not least, the lightweight/Low Mass bolt carrier group rifles (BCG) are built for ultra-light competition guns that need a number of other parts in order for it to function properly. Accuracy and precision tuning are also required in order for it to run at its best performance.
Other Kinds of Bolt Carrier Groups (BCG)
From full auto to lightweight bolt carrier groups (BCGs), different coatings, MPI inspections, and more, there are simply too many kinds of BCGs that are currently available on the market. It can make you go crazy just to determine which kinds are the best for you.
Full Auto and Semi-Auto Bolt Carrier Groups
First and foremost, the ever-known full automatic (or full auto for short) BCGs are perfectly legal and do not mystically make your AR 15 automatically start firing. The marginally longer and heavier bolt carrier group (BCG) has an additional lug at the back end of the bolt carrier group.
On a full auto AR 15 or M16 rifles, this rear lug thrusts the sear goes downwards that allows for full auto (or burst) fire. In a semi-automatic rifle, this has zero effect on how the rifle works. Semi-auto carriers are now considered as the ugly step-child of the BCG world and do not serve many purposes similar to commercial buffer tubes and stocks. The semi-auto ones have an additional cut that takes out some of its mass.
Mass that should basically help with dependability. Semi-auto versions used to be meaningfully cheaper than FA versions, however, in present-day the difference isn’t as radical. The main takeaway here is to get yourself a full-auto weighted bolt carrier group (BCG) rifle if reliability is a big concern for you.
Mil-Spec Bolt Carrier Group
Mil-Spec is considered as a bit of a buzzword in the assault rifle (AR) community. Mil-Spec basically means that the rifle is built to pass military specifications. By “mil-spec”, it does not mean the greatest ever or the worst. It basically means that it is in spec to a military personnel contract. Here are some of the important parts:
- High Pressure Tested (HPT)
- Magnetic Particle Inspected (MPI)
- Heat treated and shot-peened
- Bolt carrier machined 8620 steel
- Carpenter 158 steel bolt
- Chrome lined interior bolt carrier key and bolt carrier
- Torqued and staked gas key screws
- Coated with a matte black mil-spec finish
HPT and MPI Tested BCGs
Have you seen a bolt carrier group (BCG) rifle with the phrases “high pressure tested” and “magnetic particle inspected” imprinted or engrained into a rifle? That simply means that each bolt is individually tested at a proof load. Usually, it is printed onto the bolt (either as MP or MPI). However, it is not printed on it all the time.
If it does not say in the rifle’s description, then it probably is batch tested only. And you will never know if a batch is of 10 or 1000 BCGs. But then again, if it is a duty or self-defense gun, then most pro-gun handlers will rather opt for something that is MPI and HPT tested.
Mil-spec basically means phosphate coated and is matte in its shade, and are a little bumpy. This means it does its job, but it does need more cleaning than most newer coatings.
New coatings come and go, and most gun owners will say they are the latest and the greatest. However, here are what we think of it:
- Nitride is black and shiny. It is easier to clean than others.
- While Nickel Boron (NiB) is silver and shiny. It is as easy to clean than the others.
- The more “exotic” choices like Titanium Nitride (TiN) are “gold-grade” and pretty. And it is also easier to clean too.
The Benefits of Upgrading a Bolt Carrier Group
There are plenty of reasons why you should upgrade to a bolt carrier group (BCG) rifle. Here are some of the reasons why you should – off the top of our heads.
Improved Reliability. A weightier steel bolt carrier group (BCG) increases the guns’ cycle time and helps reduce the stress on the spent brass. This is considered a benefit to those who choose to reload. It results in a grouping better able to digest a diversity of ammunition and ammo with marginal modifications. A steel bolt carrier group (BCG) is frequently used by the military and law enforcement to battle the huge number of rounds shot.
Improved Durability. The usage of titanium or one of the accessible coated/plated carriers can be of advantageous use. Titanium is known to be lightweight and sturdier than steel. Having said that, it is better accomplished of withstanding higher heat and the risky pressures found among hotter loads. Titanium is considered to be the most expensive material and the toughest to be applied to the rifles. Because of that, its production is the most expensive. A coated/plated BCG has a waterproof surface and is a lot more convenient to clean, which often requires almost nothing more than your regular cloth rag.
Increased Speed. A lightweight bolt carrier group (lightweight BCG) rifle made from titanium or anodized aluminum reduces its weight and mass. Having said that, the gun will cycle faster and you will get a more rapid rate of semi-auto fire. Along with control acquired through practice, this can prove beneficial in any fast-paced competition.
Improved Action Smoothness. Using a lightweight bolt carrier group (lightweight BCG) rifle that is a combination with a compatible buffer will provide a lighter, smoother cycling feat. If combined with advanced coatings such as Nickel Boron, Diamond-Like Carbon coating, or Black Nitride, you will find yourself enjoying an oilskin surface and reduced friction, hence generating a smoother action.
How to Choose a BCG: The Criteria
Since the bolt carrier is the basic functioning part of a AR-15 rifle, it should perfectly deliver maximum performance. There are several important criteria you must consider before opting for a bolt carrier group (BCG) for your rifle.
First and foremost, one of the most important things to consider is the material. BCGs are, more often than not, made of steel. Although BCGs made of aluminum, titanium, and hybrid models are also obtainable on the firearms market.
The steel material rifle is further categorized into dissimilar classes. However, the most common ones for producing BCGs are the 9310 and Carpenter 158 Steel. The BCG experiences plenty of heat and stress and these steel variants fit the job really well. They are easy to machine and are readily available. The 9310 Steel is strong and durable, and it is widely used by a lot of manufacturers these days for BCGs.
The Carpenter 158 steel, on the other hand, is quantified by the military for their use. It is sturdy with high core strength and hardiness, along with exceptional water resistance.
Heat Treatment and Shot Peening
Materials used for manufacturing BCGs have to be properly treated and processed to deliver maximum performance. Heat treatment refers to exposing the steel to extremely high temperatures and then cooling it to divulge tensile strength and remove weariness.
Shot peening is the process where tiny metal balls are shot at the steel to release stress from the metal. A BCG that has underwent heat treatment and shot peening guarantees you of its forte and high quality.
Inner Chrome Lining
According to a mil-spec BCG requirement, the bolt carrier group (BCG) has to be chrome-lined on its inside. This offers a slicker and corrosion-resistant surface on the inside, which increases the life of the BCG and makes it a lot easier to clean. Most manufacturers line the BCG on the exterior, but not on the inside. You just have to make sure that you purchase the inner-chrome-lined version.
The bolt carrier group (BCG) undergoes and experiences huge gas pressure every time a shot is fired. The gas key is fortified to the carrier with the help of two hex screws, which also stop the gases from fleeing. These screws are gambled (metal on their sides is smashed into them), hence they cannot shift due to the high gas pressure underneath. This also removes the chance of any accidental disappointments in the future.
HPT and MPI Tested
To safeguard the value and reliability of their product, producers will often put their BCGs through two very laborious test procedures to locate any faults in the products. These methods are namely: HPT (High-Pressure Testing) and MPI (Magnetic Particle Inspection).
Under HPT, a high-pressured trial cartridge (usually higher than normal service loads) is fired from the BCG. The BCG further underwent detailed examination for any wear, malfunction, or cracks in the metal.
In MPI, the bolt is positioned between the poles of an electromagnet and saturated with a hold-up of magnetic particles. Using a UV light, the BCG is then reviewed for any wear or malfunction.
These examinations can be done on any individual BCGs at any given time or in batches. Try to find a BCG that has been individually tested, as it visibly translates to a proper inspection of a product.
Weight is often an area of concern when it comes to firearms. Choosing a lightweight BCG over a typical one can mean a considerable difference (up to six ounces) in its weight. However, there are certain circumstances to it.
Lightweight BCGs, apart from being low-mass, also help in bringing down and decreasing recoil. That is because the BCG travels toward the shooter when a shot is fired. Lightweight BCGs are not for the average gun handler and are more useful for competition shooters, especially when it comes to semi-auto firing.
Using a low-mass BCG coerces you to make numerous changes to properly tune your rifle. On top of that, they also restrain you to using explicit kinds of ammunition and other ammo.
Review of the Best AR-15 Bolt Carrier Group (BCG) – Our Top List
Now that we are done with the basics of what bolt carrier groups are, here is a list of some of the best BCGs you can find on the market. Best to pick 1 that fits your needs well.
1. WMD Guns NiB-X Nickel Boron AR-15 Bolt Carrier Group
Another excellently rated AR 15 bolt carrier group / AR 15 BCG originates from WMD Guns with their NiB-X Nickel Boron contribution. It comes in choices of a Mil-Spec full auto or semi-auto version, or it comes with or without a hammer. Either one (1) will lawfully drop-in your AR 15 bolt upper and operates without fail. The WMD registered NIB-X Nickel Boron finish is robust, reliable, corrosion-resistant, and super smooth. It inhibits carbon fouling from penetrating, therefore, it is very stress-free to clean. By having this finish, it delivers the best BCG for AR 15 high volume fire rates, especially when suppressed or run in a short-barrelled get-up.
The WMD Guns NiB-X Nickel Boron bolt carrier group has to pass a strict Magnetic Particle Inspection before it can attach the WMD brand. This procedure will sense the tiniest flaw, even under the surface. Hence, when you get your hands on one (1) you know you have in your hold a high-quality bolt carrier group. Even its gas key is made from tool steel and correctly staked with Grade 8 hardened fasteners, not Locktite. That means you can be sure that it will stay where it is supposed to. With a WMD part, you can expect nothing less than the greatest – which is this Nickel Boron rifle.
2. Spike’s Tactical M16 Lightweight Nickel Boron BCG
When you are currently in the market for the best lightweight AR 15 bolt carrier groups, you should have a look at Spike’s Tactical M16 Nickel Boron Bolt Carrier Group. The bolt carrier group is one (1) of the most mission-critical mechanisms of your weapon. Having said that, it will be silly to go low-cost and choose the second-best or worse than that some artificial components from overseas. This is about the best low mass AR BCG that is obtainable in the full auto M16 profile.
This Nickel Boron rifle is certainly an easy drop and swap into your M16 or AR15 rifle and will run faultlessly in either full-auto or semi-auto mode. Just like any M16 rated bolt carrier group you will find a masked firing pin inside. Many gun owners swear by this design mostly because the M16 style shrouded firing pin is not possible to puncture your primers, as you can envisage, that blowouts are no fun.
This top-rated bolt carrier group is Nickle Boron coated both inside and out. It offers a finish that is smoother than chrome ever risked to be, that will never chip, peel, or flake away. A lot of gun owners will not be surprised if you looked up glossy in the dictionary and it said: “see Spikes Tactical Nickel Boron Bolt Carrier Group”.
This Nickel Boron BCG comes with Spikes Tactical Lifetime Warranty that was netted, not given. It certainly is a good-looking, hard-working BCG that you will be very proud to have one (1).
3. Brownells M16 Mil-Spec MP/HPT Bolt Carrier Group
The majority of gun handlers were pretty happy with this BCG. Once they managed to get their hands on this and installed it, they were able to get their rifles working without any consistency issues to mention of. One gun user said he was able to install this in a few short minutes’ time without having to do any supplementary fitting.
This bolt carrier group may be considered as one of the most affordable BCG on the market. Yet, it is also considered to be one of the most resilient. Not a pretty bad venture if you want something that will last you quite a period of time without breaking your bank. This BCG was manufactured to work for the long haul. So if you are frequently using your AR 15 for hunting or target shooting purposes, then you can install this in no time and be able to keep it running for many years to come.
This is a fully-assembled, full auto bolt carrier group made and distributed from Brownells. The bolt has been manufactured from Carpenter 158 steel and the carrier has been made from hardened 8620 steel.
The bolt has been heat-treated and shot-peened to add forte to the metal. The gas key screws have been correctly torqued and staked. The manufacturer asserts to have conducted MPI and HPT testing on its 8620 steel, however that has not been printed on the BCG. However, since it comes from Brownells, this claim can be readily recognized.
The internal side has a chrome lining for lengthy service life and easy cleaning. The BCG comes with a mil spec standard phosphate finish, which is pretty much the motive for its low price. It comes with a shrouded firing pin to protect it from any possible damages. This model is a standard bolt carrier group (BCG), which can be seen as a simple, low-cost spare part for your existing bolt carrier group (BCG).
This can be a perfect option for those who are on a budget and are in search of a great BCG. If you are looking for something that is excellent in quality and will not take a huge chunk out of your savings, then you may want to consider this BCG as your best possible choice.
The Brownells Bolt Carrier Group may be exactly what you are looking for if you need a BCG that is durable and within budget. You will certainly be surprised by how long this will last you. So you are not settling for a cheap, flimsy BCG that will not last forever.
4. JP Enterprise Full Mass BCG
This is one of the top-rated and best AR 15 bolt carrier group that is also a drop-in replacement for your weapon. It is completed with stainless steel made of a superior quality quench, polish, quench nitride finish. With that being said, it gives increased lubricity and diamond-like carbon hardness along with enhanced corrosion resistance.
At the same time, it features an extended forward assist serrations and a dust cover notch this bolt carrier group that provides increased versatility and performance. All of its sharp edges are rounded and its bearing surfaces are amplified 100% for smoother operation and longer life. When properly oiled, this high-quality BCG will make your AR 15 operate like chained lightning.
This is well-thought-out to be one of the best AR BCG by many gun handlers and does not disappoint on any level. Along with this carrier comes many years of shooting and engineering experience, which gives you every advantage of a Mil-Spec part and much more.
The larger-than-life design comes together with a faultless finish to produce a flawless bolt carrier group. With its implausible engineering and high-quality this could easily be seen as one of the best AR 15 bolt carrier groups that are currently on the market. These are available as just a carrier or a complete bolt carrier group that comes as a feature of the JP Enterprises AR 15 Enhanced Bolt Assembly. It being easier to clean and compliant superior accuracy than your standard Mil Spec part makes choosing this JP Enterprises Full Mass Bolt Carrier Group an easy choice.
The bottom line is that the bolt carrier group is the heart of the AR 15 best carrier bolt rifle. It comes with a gas impingement design that achieves firing, ejection, and cycling of rounds successively. Factors such as weight, staking, inner lining, and testing must be taken into consideration before choosing a BCG.
A full auto BCG is largely preferred in this present day due to its versatile nature and shrouded firing pin. Low-mass best AR 15 bolt carrier groups, on the other hand, have their own pros such as lesser recoil, however, they largely suit competitive shooters. Individually tested bolt carrier groups from a well-known manufacturer highly expand your chances of buying a good bolt carrier group.
Every best AR 15 bolt carrier group has its own pros and cons. It’s normal that it has its own pros and cons because that’s what most products have, including rifles. Some come with adjustable gas blocks, while some others do not have an adjustable gas block. It’s the same thing how some prefer low mass BCG and some others do not prefer low mass BCG; one that comes with a mil-spec (or no mil-spec), or one that is full auto. It’s all in a person’s preferences.
Frequently Asked Questions (FAQ)
Here are some frequently asked questions (FAQs) some people may have about having the best AR 15 bolt carrier group.
Q: Does Bolt Carrier Group (BCG) affect precision in AR15 rifles?
The bolt affects precision in a AR-15 rifle more than it does the carrier group. To maximize the capacity of precision, the bolt and barrel will have to be machined so that the head-spacing is at its maximum when the round is chambered and the bolt locked.