There are two schools of thought when choosing the best AR-15 bolt carrier group for your rifle. The first school says the bolt is the only thing between your face and a small explosion, so it should be high quality.
The second school of though takes a more… relaxed view of things.
The second school says they’re pretty much all the same so get whatever is cheapest and it’ll work just fine. And it’s true most of the time.
But sometimes…
Personally, I think the second school of thought is just plain stupid because for a few dollars more ($10-$20) you can get a VERY high quality BCG.
I only have one body and I plan on keeping it for a long time.
(NOTE: This article is part of my "Best in Class" series where I list the top choices for various parts of your AR-15. You can find the other parts here: Best in Class Articles.)
Requirements for the Best AR-15 Bolt Carrier Group
(You can skip this section if you just want a recommendation and don’t care about the nitty-gritty tech stuff.)
I devoted a chunk of my AR-15 build guide article to the requirements for a great bolt carrier group. But I will repeat them here to save you a click and some scrolling.
The most important factors are the type of steel and the heat treatment. Carpenter 158 steel and 9310 steel are the best choices and are fortunately the most common. For a while, some people were making bolts out of 8620 steel which is NOT acceptable. 8620 steel is much weaker and you can break your bolt with hard use.
While you shouldn’t make the bolt from 8620 steel, It’s the correct steel for the carrier. In fact, 8620 is mil-spec for the carrier and has worked perfectly for over 50 years.
It’s also very important to make sure the bolt carrier has a shrouded firing pin.
If you look at the picture, you’ll notice that you can see the firing pin on one carrier, but not on the other. The left hand carriers have shrouded firing pins.
A shrouded firing pin is VERY important because without it, all the force used to cock the hammer is applied to the firing pin.
An unshrouded firing pin causes excessive wear on both the firing pin and hammer and can easily break your firing pin with hard use. By contrast, a shrouded firing pin allows the carrier to take the force and apply it more evenly to the hammer.
All “Full Auto” or “M16” bolt carriers will have a shrouded firing pins.
To get the best bolt possible, there are other things to look for. (these only apply to the bolt, not the carrier) You want a bolt that’s MPI and shot peened. MPI stands for “Magnetic Particle Inspected” and is a quality control measure that ensures you’re getting a high quality bolt.
Shot peening will ensure:
“the finished part will resist fatigue failures, corrosion fatigue and cracking, and galling and erosion from cavitation.”
For non-engineers, that means it will keep it’s strength over time.
(NOTE: Another common quality control measure is “HPT”. HTP stands for “High Pressure Tested” and refers to firing a way over-pressure proof load to ensure the bolt is strong enough. Back in the 60s, this was essential. Today, modern manufacturing techniques have rendered it nearly obsolete/unnecessary. It’s not bad, but shooting a WAY over-pressure load doesn’t like the best way to maximize bolt life…)
Now lets look at some great BCGs.
FYI: If you buy after clicking most of the product links on this page, I'll make a few pennies out of each dollar you spend. It's not much, but it keeps the website going and I would appreciate your support. 🙂
Brownells M16 BCG
Every so often, you find a great product at an incredible price and that’s the case here. The Brownells m16 BCG is hands down the best AR-15 bolt carrier group (for the money) I’ve ever seen.
(To be clear, I’m not saying this is the best BCG that anyone makes and it beats all others in quality. But it has everything done right for a price that’s almost unbeatable.)
They got it right with this one:
- Every Bolt is Magnetic Particle Inspected (MPI)
- The Bolt is machined from 9310 steel
- Following machining, the Bolt is heat treated and shot peened
- M16 Bolt Carrier is machined from 8620 steel and hardened
- M16 Bolt Carrier will function in semi-auto or full-auto AR-15/M16
- The Gas Key Screws are properly torqued and staked
It checks every single box and is less than $100. 🙂
Even better, they upgraded the finish from mil-spec.
The mil-spec finish for the bolt and bolt carrier is called “parkerizing“. Parkerizing is fairly corrosion resistant but is also extremely porous. The surface is not smooth, but is full of tiny (microscopic) holes like the surface of a sponge. These pores soak up and hold oil very well, which accounts for most of the corrosion resistance.
However…
The porous surface is also relatively rough. That leads to increased friction and heat during operation. Also, those pores love to get clogged with dirt and carbon. Because of that, it’s harder to clean a parkerized surface than many other surface treatments.
Instead of the mil-spec parkerizing, they gave this BCG a nitride finish.
Both Melonite and Tenifer are names for nitride treatment and both are widely used in industrial applications and on gun parts, especially pistol slides. (Glock uses the Tenifer and S&W uses Melonite on the M&P series.) If you want some more information, I found a Youtube video to give you a better idea.
The short version: it’s one of the two best BCG finishes available.
Nitride treated steel is very smooth, very hard, and extremely resistant to corrosion. The smoothness is a great thing because it reduces friction, which reduces heat too. Also, nothing sticks to it very well meaning it’s much easier to clean. Plus, it’s a treatment not a plating/coating so it can’t chip, crack or peel.
All things considered, this is probably the best AR-15 bolt carrier group for the money.
And if it doesn’t float your boat for some reason, just take advantage of the Brownells “100% forever” guarantee.
If you aren’t completely, 100% satisfied with any purchase you receive from Brownells, for any reason, at any time, return it for a full refund or exchange. No hassle, no problem. And, we won’t bog you down in endless paperwork. Your complete satisfaction with each and every product we sell is what’s most important to us.
With a warranty like that, how could you go wrong?
BCM (Bravo Company Manufacturing) M16 BCG – $169
If you want a combat proven BCG, look no further than the BCM M16 Bolt Carrier Group. BCM has acquired a well-deserved reputation for making very high quality parts.
In fact, BCM’s about page says:
Bravo Company USA, Inc.’s Previous Customers Include:
HQ SOCOM (Special Operations Command), US Army, US Navy, US Air Force, US Marines, US Coast Guard, various Special Operations Units, Department of Homeland Security, US Border Patrol, American Embassies, Private Security Companies, Law Enforcement Agencies and Tactical Units, and responsible civilians.
Needless to say, they get the details right.
You can look at any review anywhere, and you’ll find plenty of people who are so happy they won’t buy anything else. That – plus the fact that our military and even special forces have used their products – should tell you something.
In fact, BCM takes quality control so seriously that they fire ever BCG before they ship it out. (So it might have marks and/or be dirty when you get it.) Objectively speaking, I can’t point to anything that says the BCM is any better than the Brownells… other than the name.
But the name counts.
BCM has a great reputation for a reason.
Many people have tried it, (torture) tested it, and it’s absolutely top shelf. It just plain works no matter what. So if you kick down doors for a living, I’d take a hard look at them. If not, I’d save almost $70 bucks and get the Brownells BCG
At this point, I run into a problem
In my Best in Class series, I usually list about a half dozen products at different price/quality levels to give you options.
However…
You won’t gain much from a more expensive bolt carrier group. The only way up from here (and not everyone agrees it’s going up) is a Nickel Boron plated BCG. (and possibly Nickel Teflon, but the jury’s still out on that.) However, Nickel Boron is hard to coat properly and only a few companies do it right. Those companies charge at least $150, and usually more like $180 – $200.
Side note: if you see a Nickel Boron BCG for under $150 – and especially under $100 – I would stay away. The odds of them doing the plating correctly are very low. Cheap Nickel Boron plating can crack, chip or peel and cause function issues.
Both Nitride and Nickel Boron are much easier to clean than the standard parkerized finish. For Nickel Boron, I typicall use a paper towel and (maybe) a little CLP to get one clean. Nitride is very easy to clean too. Both are light years ahead of the traditional parkerized finish.
Some say Nickel Boron plating – when properly applied – is better than Nitride. I’m not convinced it’s better, and it’s definitely not twice as good. (Not even close.) So is it worth almost doubling the cost?
In most cases I would say no.
There are other coatings on the market, but most of them just don’t have the longevity of Nitride and Nickel Boron.
- Chrome plating. Good, but chrome is a lot stickier than most people think. My grandfather was a Hydraulic engineer at Caterpillar for decades, so he knows a thing or two about it. (they chrome plate the pistons). Long story short, Nitride is a better way to go. It causes less friction, can’t crack, chip or peel, and is usually cheaper too. (NOTE: the inside of the BCG’s gas key is almost always chrome plated per mil-spec)
- TiN (Titanium Nitride). Not a good choice. The most common use you’re probably familiar with is coating drills bits. While the gold color is pretty cool, the coating is very thin and prone to wearing off quickly.
- IonBond and other PVD (Particle Vapor Deposition) Coatings. They apply carbon to a surface in a manner that makes its’ structure resemble a diamond. Diamond is one of hardest, strongest and slickest materials we know of, so the theory sounds good. I bought a PVD coated BCG to test. However, I got a warranty replacement after less than 200 rounds because the finish was coming off. I haven’t tested the new one yet. I would personally avoid PVD coatings at this point.
- Nickel Teflon (NP3). I still haven’t made up my mind about this one. Nickel Teflon is more slick than most platings, but it’s also much softer. I have a Nickel Teflon coated buffer on my AR-15 and it has a few small dings from the buffer retaining pin. I’ve heard it wears well on a BCG, but I don’t have enough evidence to say Yea or Nay right now. They will run you almost $200.
That covers advanced BCG platings/coatings.
WMD Guns M16 NiB-X Bolt Carrier Group – $189
If you want to get a Nickel Boron Bolt Carrier Group, the only company I’m sure plates them correctly is WMD Guns. That said, if you buy from any of the tier one makers, you should get something good.
WMD Guns has their own proprietary version they call “NiB-X”. Their NiB-X plated M16 BCG is the one I recommend if you want a Nickel Boron BCG.
One more thing:
No matter what the advertising says, please don’t EVER run your AR-15 dry (no oil) no matter what coating/plating you have.
There is a VERY large gap between what “can” be done, and what “should” be done.
Can you run Nickel Boron BCG without oil and be reliable? Yes. However, you should never run any BCG without lube. Even if the BCG doesn’t suffer, the upper receiver should definitely have oil regardless of the BCG.
Conclusion
For the vast majority of us, the Brownells BCG for under $100 is probably the best choice. It’ll work well as the heart of your AR-15 without draining your wallet. If you ever have a problem, Brownells has their 100% forever guarantee to take care of you.
If you’re an LEO or military, the BCM gives you a lot of confidence in your equipment.
And that’s about all I have to say.
The best AR-15 bolt carrier group for you might not be the best for me. So pick the one that fits your needs and happy shooting. 🙂
Another plus to nitride finishes, that I just learned about; if the black surface finish wears to shiny metal the notifying is still there. Including all of its anti corrosion and hardness properties.
Abe, I read somewhere that the bolt and BCG should be from the same company as the barrel in order to align itself when engaged. Also, the BCG I’ve had in mind has a NP3 finish. Finally, the barrel I want is stainless steel and is not chromed lined. Will this process create a problem after extensive use? Thank you for your help.
If the both the barrel and barrel extension are in-spec and assembled correctly, then any in-spec BCG will function perfectly. If you want the greatest possible accuracy, then the bolt can be matched with a specific barrel. They don’t have to be made by the same company, just matched to each other. However, unless you’re doing really high level competition I doubt you’ll notice the accuracy difference.
The NP3 coating’s only weakness is how soft it is compared to other finishes. I’ve heard it works great, I’m just not 100% sure.
Chrome lining greatly increases barrel life. It’s not that stainless steel will wear fast, it’s that chrome will wear much more slowly. Usually around double if my memory serves me. However, most people will never fire enough rounds to worry about it.
078-000-328WB
M16 B-TAC Bolt Carrier Group 5.56 MPI/HPT 9310 Nitride
Discontinued by Brownells
Product has been discontinued and no longer available.
I’ve updated the article and thanks for catching that. 🙂 It looks like Brownells is replacing the B-TAC with a new one. The new one doesn’t have the High-pressure test performed, which basically means shooting one or two over-pressure rounds to ensure the bolt doesn’t fail. I don’t *think* this is a problem because the bolt is still magnetic particle inspected. Obviously I haven’t tested one though.
The BROWNELLS M16 B-TAC BCG is apparently discontinued. The replacement bolt is more money with similar specs Carpenter steel bolt though, 140 bucks, the phosphate one is cheaper. Is the following apparent replacement bcg the same thing? Do you have an affiliate link to this one? Is it now a good Idea to spend the extra 30 bucks for the BCM, since the B-tac is discontinued?
BROWNELLS – M16 MIL-SPEC MP/HPT BOLT CARRIER GROUP pecs:
Fully assembled Bolt Carrier Group; including the bolt, bolt carrier, gas key, firing pin, cam pin, and firing pin retaining pin
Every Bolt is High Pressure Tested (HPT) with a proof load
Following the High Pressure Test, every Bolt is Magnetic Particle Inspected (MPI)
Not stamped with HPT or MPI
The Bolt is machined from Carpenter 158 steel
Following machining, the Bolt is heat treated and shot peened
Installed extractor includes red o-ring with spring
M16 Bolt Carrier is machined from 8620 steel and hardened
Interior of Bolt Carrier Carrier Key & Bolt Carrier are chrome lined
M16 Bolt Carrier will function in semi-auto or full-auto AR-15/M16
Gas Key Screws are properly torqued and staked
Bolt and Bolt Carrier feature a matte black mil-spec finish
If you were going to spend $140, then yes I would just spend the extra to get the BCM. That said, Brownells looks like is replacing their B-TAC with a new version. You can check the article or comment above for more info. Clicking any affiliate link on the website will tag your browser for 30 days. It doesn’t need to be the link for a specific product.
Great article. I’m of the first school of thought. I also run a Mega arms thick-wall upper receicer. It’s not much more cost or weight, but a LOT more aluminum between me and a kaboom.
Brownells is offering a Nickel Boron BCG for $110. Per this article, would you trust Brownells to have performed the Nickel Boron coating correctly? Here is the BCG in question:
http://www.brownells.com/rifle-parts/bolt-parts/bolt-carrier-groups/m16-5-56-bolt-carrier-group-nickel-boron-mp-prod105378.aspx
I’m weary to purchase the BCG linked above over the following BCG due to what you said about coating. Right now, the below Nitride M16 mil-spec BCG is on sale for $30 off, so it is $110 just like the Nickel Boron BCG:
http://www.brownells.com/rifle-parts/bolt-parts/bolt-carrier-groups/m16-mil-spec-mp-hpt-bolt-carrier-group-prod78714.aspx
Which one of these would you recommend?
I would personally go with the Nitride BCG… But partially because I like black. Nitride is easy to do correctly and rarely done badly, whereas I don’t know who does their Nickel Boron plating. In general I’d trust Brownells products though. One of the things I REALLY love about Brownells is their “100% forever Guarantee” To quote from their website:
So don’t feel bad about giving it a try. They have you covered pretty much forever if you have a problem. (You’ll notice that almost every product link on this website goes to Brownells; their guarantee is part of the reason)
Awesome, thanks heaps for your reply and for the outstanding articles.
Shouldn’t titanium carrier be at least part of a Best In Class discussion?
The only reason to go Titanium is lighter operating parts. However, if you want to get any advantage at all, you need more than just the BCG. You need to properly tune the buffer weight, spring power, use lower-power ammo, and install an adjustable gas block. When all those forces are balanced perfectly, then lightweight BCGs makes some sense (lower total energy entering the system=less recoil). However, one of the AR-15’s original designers said himself that lighter operating parts “is just crazy”. (video here, start at around ~4:45)
From a reliability and pure physics perspective, heavier is better. It’s much more tolerant of ammo changes and dirt/crud and – when your gas system is properly tuned – also reduces recoil. There’s a thread on the AR-15 forums that talks about this in exhaustive detail.
Abe, with all due respect I think it’s highly irresponsible to link a dated thread from 2014 of a bunch of high school kids debating for only two pages on theory and mathematics versus current proven experience from noted firearm experts that actually understand the science behind it. Moreover, the linked thread is almost four years old and since then, albeit with a proven low mass/lightweight bcg, a precision adjustable gas block and a lightweight buffer it’s now proven when done right not only does it greatly reduce felt recoil, but the parts can last just as long as their noted-heavier predecessors. I personally would suggest either the Faxon or Rubber City bcg, the SLR Sentry 7 or Superlative Arms adjustable gas block and a Taccom lightweight buffer. When properly tuned, which is a very simple, and while testing with lower quality ammunition the operator shouldn’t encounter any problems later on.
As for your reference to “more mass equivalents to more reliability” since the creation of that outdated thread we–as in through those who know better than myself–now know that’s only a half-truth and it’s much more complicated. Also, when discussing reliability and subjected conditions context needs to be established. Most readers aren’t military personnel and Leo’s, so their gun range rifle won’t need the same level of consistency, i.e: one f.t.f every thousand rounds isn’t going to mean all that much to them.
The only thing(s) I’d advice is when going low mass/lightweight make sure to do a lot research before deciding on anything, learn exactly how to properly tune your gas system and avoid all aluminum bcg since aluminum wears far too quickly for the average shooter(they’re usually reserved for competitions).
I’m not sure we actually disagree on anything except whether it’s proper to link to forum posts. I agree that a properly configured lightweight system does reduce recoil (and said so). It can also be quite reliable when properly tuned. A properly configured/tuned heavy system can also reduce recoil. It’s all about balancing forces, which can be done with either.
My research has led me to believe a higher mass system will have slightly higher functional reliability rates because there is more momentum. James Sullivan takes this opinion, as have others. I don’t claim to be an expert, but I do think I understand the physics behind it. If you have a good source for conflicting data, I would love to read it because I’ve been wrong many times before. (and because Gun design is one of my many passions).
Bravo company manufacturer in no way supply’s or supports the military they use that tactic to sell more to the unknowing consumer. Military primary uses Colt and FN. I am servicing 19 years and have yet to come across anything bravo company. They really should take that off their site borderline stolen valor
Just because they don’t have a contract to supply M4’s that FN and Colt does at this time, doesn’t mean they don’t supply the military at all. They state that their customers include “HQ SOCOM (Special Operations Command), US Army, US Navy, US Air Force, US Marines, US Coast Guard, various Special Operations Units, Department of Homeland Security, US Border Patrol, American Embassies, Private Security Companies, Law Enforcement Agencies and Tactical Units, and responsible civilians.” If you doubt their claim, then simply ask them to supply the GSA or NSN number for the parts they claim to sell to the military. If they wont (or can’t) supply that to you, then you can make the assumption that you have made. But without knowing that, it’s only an assumption. Keep in mind that Bravo Company is mostly a distributor and not a manufacturer. All they need to do is sell any of these customers something like a MagPul PMAG magazines, and that justifies their claim… that they are customers. But if they aren’t customers then it isn’t Stolen Valor, it’s false advertising.
I have a half dozen BCS mags made with the old LaBelle tooling and the products, just like Magpul PMags, have a Cage Code supplied although National Stock Numbers usually aren’t needed for non-government entities. I have worked with federal parts and stockroom systems for years in a GSA capacity and having a Cage Code for a product that has no NSN is like putting a VIN on a skateboard. Remember, there are subgroups (not standard infantry) running completely different rigs with different parts and creating things like the SPR and the like which are purpose built weapons for a limited military population. Before you malign the company, you should ask for the NSN casually. Since you seem to be in an armorer/quartermaster capacity and handle inventory, it’s likely they’ll be more than happy to give it to you.
You’ve tested one PVD type BCG, had a problem, had it replaced but didn’t test the replacement and recommend against PVD coated BCGs… So much for objectivity. Just to clarify, PVD is not always DLC, however, DLC is always PVD. PVD stands for Plasma Vapor Deposition, that can include any number of different coatings types, just one of them being DLC (Diamond Like Coating). DLC is nearly as hard as a diamond, and has a lower friction coefficient than just about any other coating on the market. If it’s done right (because with any type coating it is 95% preparation and 5% coating), it doesn’t come off very easily and can be run completely dry. I suspect what you tested was not DLC or IonBond (which is simply a trademarked name for a particular type of DLC coating process). For an objectivity, you might want to state exactly what brand BCG you had that failed, and perhaps recommend against that particular brand instead of all PVD coated BCGs, and perhaps only do that after you fully tested the replacement since they did replace it…
Hello Abe,
Just a quick question my friend? I am NEW to the AR Platform, so my question may sound ignorant, but I was recently gifted an E-BCG by LANTAC, and was curious if you knew the stats on this Bolt Carrier Group, and where it ranks, Quality Wise?? Thanks for your time, and I hope to hear back from you?
Sincerely, – JAY –
I don’t have any personal experience but the specs look about right. It looks like a high-quality BCG, so I would use it and enjoy. 🙂
I just enjoyed reading this blog. I regularly visit your blog and every time I found & learn something different on guns/firearms/rifles/accesories topics. So I want to thank the admin for putting your efforts in making this well-developed post and I’m looking forward for more post like this.
If the both the barrel and barrel extension are in-spec and assembled correctly, then any in-spec BCG will function perfectly. The most important factors are the type of steel and the heat treatment. Yes, I also agree with the same point that It’s also very important to make sure the bolt carrier has a shrouded firing pin. They selected Bolt Carriers with Reliability Cuts which allow debris and carbon to collect in specific areas away from the rails the BCG rides on rather than collecting on the rails and gumming up the action.