American Built Arms Bolt Carrier Group

When shopping for BCG’s for an AR 15 build there are many who are of the opinion there’s not much difference between them other than price. If you do your homework you’ll find there aren’t that many companies making complete bolt carrier groups or the bolts themselves. The majority of companies selling AR’s purchase these parts from companies specializing in the manufacture of BCG’s and other AR parts.

The vast majority produces these BCG’s in the same manner. Using standard machinery the carriers are made then sent off for heat treatment. On return these companies have people trained to do handwork in order to get the bolt carrier and bolt back into spec. For instance the collar on the bolt itself is very critical in proper operation of the entire unit. This collar has to be hand turned to return it to spec. A lot of handwork means more time, which translates to a higher price depending on the purchasing, companies’ requirements and materials used. Extra units are made to compensate for those found to be defective. Most medium priced AR’s use BCG’s made in this manner.

I was looking for something better and found it in the American Built Arms BCG and the bolt itself. This company is veteran owned and they are very particular in the products they sell.

Mil Spec 5.56 Bolt Assembly  Nickel Boron Coated  shot peened with Carpenter 158 steel.

AB Arms uses a manufacturing process different than other makers of BCG’s and bolts. The company uses “Swiss” machinery, as they call it, to make their parts. The “Swiss” machinery uses a rotating method of cutting which AB Arms tells me is much more precise than the use of standard machinery used in most of the industry. This machinery is a good deal more expensive but turns out a much better product. Made to closer tolerances means less or no work performed on the parts after heat-treating.

5.56 Mil Spec Bolt Carrier Group 3 Nickel Boron Coated Bolt and Cam Pin

The carrier itself is chrome lined with phosphate external coating. The cam pin and bolt are nickel boron coated. These two finishes make for a very smooth action as the bolt moves within the carrier. I’ve fired over 500 rounds without cleaning the rifle and still find the unit to work as smoothly as in the beginning. When I first installed it and racked the first round into it I noticed how smoothly it worked. My first thought was no way. I put my old carrier back in the rifle worked the action then put the AB unit back in the AR. I wasn’t wrong it was that much smoother. Honestly I had a hard time believing it having never experienced that much difference in carriers before.

5.56 Mil Spec Bolt Carrier Group 2 Nickel Boron Coated Bolt and Cam Pin

After firing the 500 rounds I checked the BCG over for any signs of wear. There are none as the photos show. All of the other BCG’s I’ve used have shown wear on the parked finish.

5.56 Mil Spec Bolt Carrier Group  Nickel Boron Coated Bolt and Cam Pin

I wanted to get more information on the process they use to make these units and why they chose the finishes they use. I gave them a call and talked with Jason one of the owners.


You’ll notice on the bolt it uses a phosphate finish on the extractor. The reason for that was they found the nickel boron finish to be to slick causing some slippage as the extractor grabbed the case. They went back to the phosphate coating for greater reliability during extraction. After experimenting with coatings they found the use of nickel boron on the bolt and cam pin working against the chrome lining made it very smooth in operation and increased the lifespan of the unit.


There is almost always some information companies can’t share and my next question was one he couldn’t give me specifics on at least not that I can share. I asked which companies they sold their BCG’s and bolts to. The best answer I can share with you is the ABM BCG/bolt is used in the majority of the very high end AR’s on the market. You would certainly recognize the names if I could share them. I honestly found nothing not to like about this product. It’s well worth checking into if you’re in the market for a BCG.


At a retail of $189.00 I would consider this a very fair price for the entire BCG and bolt. The full specs are listed below.

American Built Arms

Statement from A*B Arms

“BoA*B Arms 5.56 Mil-Spec+ Bolt Assembly Nickel Boron Coated
Ready to drop into your bolt carrier group. These Bolts are specially made on high end Swiss machinery to have exacting tolerances and surface finish. A*B Arms is known by rifle manufacturers for manufacturing one of the finest quality bolts and extractors available. This has won us contracts with some of the highest quality AR manufacturers in the business. If you want to buy super high quality parts offered by the company that actually manufactures them, then you’ve come to the right place.”

Carpenter 158 Steel
Heat treated per Mil-Spec Requirements
Shot Peened per Mil-Spec Requirements
MPI Tested Material
Nickel Boron Coated

Aircraft Quality E4140 Steel
Heat treated per Mil-Spec Requirements
Shot Peened per Mil-Spec Requirements
Manganese Phosphate Coated per Mil-Spec Requirements

Bolt Assembly

Carpenter 158 Steel
Heat Treated
Shot Peened
MPI Tested Material
Nickel Boron Coated


E4140 Steel
Shot Peened
Phosphate Coated

Bolt Carrier

8620 Steel
Phosphate Coated
Chrome lined bore
M-16 Style with more mass for better functioning in semi or full auto rifles

Gas Key

4130 Steel
Black Nitride
Gas Key Screws – 4140 Steel properly staked per Mil-Spec requirements

Cam Pin

4140 Steel
Nickel Boron Coated

Firing Pin

AISI 8740 Steel
Chrome Coated


Phil White

Retired police officer with 30 years of service. Firearms instructor and SRU team member. I still instruct with local agencies. My daily carry pistol is the tried and true 1911. I’m the Associate Editor and moderator at TFB. I really enjoy answering readers questions and comments. We can all learn from each other about our favorite hobby!


  • Tom – UK

    As someone who does not own a AR-15, or any form of semi-auto but has used them and spent a couple years using the SA80 A2 I read articles like this and am impressed by the effort and thought that has gone into these products and then get two questions.

    Do the varying Bolt Carrier Groups/component parts of them that are for sale have any noticeable or significant effect on the following aspects.

    Ease of cleaning
    Service life

    By significant effect I suppose I would have to split it down into perhaps 3 groups of usage.

    Target shooting, Hunting, Home Defence

    2nd question.

    Are high end bcg’s sold for rifles like the AK-47, Tavor etc.

    Or is this just a case of people buying products which dont really do anything additional for functionality but let you have a shiny brand?

    • BoHeck

      A good bcg will guarantee reliability and long service life, slick coatings aid in cleaning and some have excellent corrosion resistance, much more so than standard manganese phosphate. The reason there are so many options for the AR as opposed to a rifle like the Tavor is that parts are coming from hundreds of suppliers, not just one company. Parts for the Tavor are made by a single company, to the same print, tolerances and go through the same quality control and will do so forever. AR parts are made by hundreds of different companies who may or may not take liberties to meet a certain price point. AKs are kind of in the same boat but not to the same degree, there are builders out there who make junk and I’ve seen mang phosphate coated bolts and chromed bolts but that’s about it. Most of the time parts kits arrive from overseas and assembled here or already imported assembled.

      • Tom – UK

        I see what you mean in terms of many manufacturers and imported weapons but my question was meant to ask “how much a difference does it really make?”

        Ie. Take a standard AR15 and then swap its BCG will you really actually experience much of a difference?

        • BoHeck

          I answered that question first in my response. You will see increased reliability, ease of cleaning and possibly corrosion resistance depending on coating. That’s about it.

          Low mass bcg are for competition rifles where reduced recoil is desired. These must be used in conjunction with tuning the gas system to cycle properly.

          For someone who uses their weapon quite a bit, such as taking many carbine classes, something easier to clean would be nice. A lot of the times it’s more about who’s name is on the side or a slick looking logo. There are only a handful of companies that mass produce these and supply them to the entire industry. Spikes, BCM, AIM, Black Rain, Noveske, Palmetto State Armory, Wilson Combat, none of these make their own BCG. The list goes on but you get the idea. Usually there’s a double markup between the selling of the manufacturer to the Vendor who engraves it with their logo and then another markup to the consumer. These guys are just making one huge markup straight to the consumer. If I buy a BCG straight from the manufacturer I really expect to be saving some cash going directly to the source. I really don’t see many BCG selling higher than $200 bucks so that tells me they are charging even more than the vendors who buy and resell their product. So no, not worth it.

          • They sell direct to the consumer but a very large part of the sales are to higher end brands of AR’s. I wish I could tell you who uses this BCG in the rifles they sell but they have an agreement with these companies not to divulge that information.
            These guys put a huge amount of time in research to ensure they make the best BCG they can. Since the guys are former military and have seen some bad gear they wanted the best for those who go in harms way as well as providing quality to the average AR shooter.

          • BoHeck

            For that kind of price I at least expect high proof testing and some coating that’s better than manganese phosphate to fight corrosion. I won’t argue it’s probably a pretty good BCG, but I disagree that it commands such a high price tag. They were successfully able to make a mil spec BCG and coated the bolt….that’s it. Sadly in today’s world where there are some really junk parts in abundance, this feat is celebrated.

        • John

          In the end, IMO what really counts are the bolt (CRITICAL) and the gas key. And what they really affect (in the end) is service life, and by derivation, reliability. What different companies do to ensure that a BCG is made properly is what governs why some people say one is better than the other. I’ll talk about the run of the mill, M16 phosphate bolt carrier in this discussion for simplicity

          For example, take HPT/MPI testing on the bolt. A proofing (overcharged) round fired with the bolt (HPT) and a magnetic powder is ‘dusted’ over the it (MPI) to inspect for any defects, cracks, etc. Some companies will perform HPT/MPI testing, others will not. Companies have claimed that the manufacturing process of a bolt have a performance-affecting defect rate of 30%. The bolt cracking/failing at the cam pin hole is the most common problem of non-MPI testing bolts. For some companies, this is acceptable, as their consumer market will not fire their AR-15 enough to reach that limit and will hence not HPT/MPI test.

          There are also differences in testing criteria, what is deemed acceptable, unacceptable, whether the company individually tests each bolt for defects, or whether they pick one bolt to test out of every 100 (batch testing) as a representation of the group, etc.

          Furthermore, some companies make their bolt out of the Carpenter 158 steel, others 9310, and [the worst] make them out of 8620 (same material as the carrier). What this translates to is bolt life before the lugs crack.

          Heat treatment also varies, and can result in bolt failure: if the material is too brittle, or too soft, it can crack, peen, and eventually lead to catastrophic failure of the rifle. This has been observed due to recent politics in the US, which resulted in panic buying and unscrupulous manufacturers producing poorly made bolts.

          As for the Gas Key, there is much debate on the matter. Having a gas key be permanently attached yet replaceable is critical for a BCG. A loose gas key can lead to short stroking, misfires, and [arguably] catastrophic failure of the firearm.

          Staking, or crimping the metal over the bolt so the bolts don’t back out (a ‘mil-spec’ process), is what most people are crazy about, Many companies have gotten wise and advertised it as a selling point, many also do not, and many more do not do it properly.

          Young Manufacturing is known for purposefully not staking their carrier keys. Instead, they use threadlocker and torque the screws to the proper tightness. Their argument is that staking =/= the screw is tight, and was mainly implemented to prevent GIs from unscrewing the gas key. Overall, people seem to give a thumbs up to Young Manufacturing’s quality, and the people who want to stake their BCGs do so.

          YFS screws have also made some controversy when talking about BCGs. YFS screws, made by the Fang Sheng Screw Co. are “cheap” screws that some companies use to install the gas key, and have been purported to shear off after heavy use and due to poor manufacturing /improper thread sizing.

          As you can see, there is a LOT that goes into making a good BCG/AR-15, and i haven’t even gotten into coating, gas rings, etc. and there can be a long writeup that I hope TFB can do. You can go on and on about the subject. I hope this sheds light on your questions and shows you that not all BCGs are made equal Low mass, and other specialty BCGs aside, the main selling point is quality quality quality

        • I have with this one especially as far as reliability is concerned. Most AR’s I’ve owned or used choke on steel cased ammo after a few hundred rounds. I haven’t experienced that using this setup with a Giselle gas block. Since making these changes the rifle has been more reliable.

        • Tom the bottom line and what you’re really looking for is increased reliability. I’d say everything else is secondary to that. Better reliability is worth the cost especially if the weapon is being used for protection. I mean reliability as it relates to function and longevity of the unit.
          If it means anything to you I intend to continue using this BCG and retire my previous BCG.

    • Cornelius Carroll

      Hi Tom,

      About improvements from a BCG:

      -Accuracy: no
      -Reliability: yes. This basically comes down to whether or not the BCG is made to mil-spec. For example some AR-15 BCGs sold in consumer-grade rifles have bolts made from 8620 steel in an effort to reduce costs. 8620 bolts are likely to fail much earlier than a mil-spec C158 bolt. Other areas of reliability are a bit more up for debate.
      -Recoil: yes. There are competition-grade BCGs (like from JP Enterprises) that are lightweight and, when combined with an adjustable gas block, can reduce the recoil of the AR-15 to almost nil. It’s remarkable really.
      -Ease of cleaning: YES! nickel boron, dlc, and chromed carriers are all much easier to clean.
      -Service life: tough to answer

      The only other weapon with “high end” bcgs that springs to mind is the Ruger 10/22 platform. With weapons like the Tavor there simply aren’t enough of them around (compared to the AR) for small manufacturers to bother with tooling up to replace/improve on a component like the BCG. The AK seems like it would be a good candidate but a well made AK seems damn-near indestructible and “tech” improvements seem to run counter to AK culture so the market probably isn’t there.

    • To answer your questions I can agree with Cornelius with one exception. I believe it does provide longer service life not only for the BCG but for the rifle itself.

    • n0truscotsman

      “Or is this just a case of people buying products which dont really do anything additional for functionality but let you have a shiny brand?”

      I would go with that paragraph and Ill tell you why.

      On paper, these guys really did their homework. Im not denigrating their effort in any way. These BCGs seem to be well thought out and very logical in their deliberate use of phosphate and nickel components.

      In reality, however, there is no empirical evidence that nickel boron or any other modified BCGs extend the life and reliability of carbines compared to the regular military specification one. If such documentation exists, someone please correct me. I have found no evidence from personal use or other tests that convinces me otherwise.

      The military frequently tested nickel boron and chrome BCGs previously and found no improvement in reliability or lifespan.

    • Rusty Shackleford
  • curt

    swiss machining? So they make them on a swiss turn? I thought that was pretty standard..

    • BoHeck

      Coming from someone who’s in the industry, yes it is very standard now to produce them this way. All of the major suppliers in the industry machine their bolts, cam pins, firing pins, ejector pins, extractor pins and even the extractor themselves on Swiss machines. So no, I do not agree with the high price tag of these, there are many bcg out there machined to the same mil spec print and tolerances with better coatings than this available.

      They check all the right boxes with materials and I’m sure they make a good bcg but simply saying it’s made on a Swiss doesn’t mean squat. I’ve seen some really crappy parts come off a Swiss because the setup was incorrect, the same thing can happen with any good machine.

      • Nono

        A little first hand experience goes a long way. Thank you

      • VolkCNC

        I too was of the impression that Swiss turn was the standard manufacturing process. Sounds to me like a case of trying to use buzz words to imply “Swiss Quality” for the uniformed. Good tools do not automatically equal good product.

      • That really isn’t what I’ve been told from several sources. I’m curious can you tell me which companies use the Swiss machines and what model they use?

        • MP

          “Sources” said the “Journalist”

          • Yes sources and there’s no need to be insulting.

          • MP

            People are calling out your truthiness. You respond with “several sources”. Do not pass go. Do not collect $200.

        • BoHeck

          Microbest, Barnes Precision, Nolte and Daniel Defense among others. I’ve met several OEM manufacturers to commercial as well as those who supply Colt and FN who use swiss and it’s becoming evermore popular.

          • So are there several models of these?

          • BoHeck

            Several models of Swiss machines? Yes there are many manufacturers of Swiss CNCs and the product lines are pretty incredible with what they are able to do now.

        • curt

          I’m in the machining/firearm industry and recently another local shop that mostly does gov contracting stuff got into bcgs.As far as I know they haven’t resold these to any other manufacturers yet or to the public,but they had no trouble going out and spending large sums of money on tooling and machinery ,specifically a Eurotech b446-sy2. My point is Ive only seen 1 bcg manufacturer in person and they used a swiss turn.It just seems like it would be standard to me. My company doesn’t bother with ar stuff normally so I don’t know what really is standard.

          eurotech in action

      • publius1969

        BoHeck, can you recommend some comparable BCGs? i am in the market for one and would appreciate your input. I am interested in better coatings than what the AB BCG in this article offers. thanks

    • No not according to them. Because of cost most go with the cheaper machines.

  • Eric

    That is actually a decent price for a good BCG that’s made in America (I’m drawing a conclusion here based on the manufacturer’s name). But 500 rounds isn’t really that good of a test. I’ve put over a 1,000 rounds through AR-15’s between cleanings without experiencing any failures. I think I’d want to see a better long term test of this product before I’d spend the extra money to get one.

    • It is American made by them. As far as round count fired we’ve covered this many times before but all writers, myself included, purchase our own ammo for these test.
      Heck if ammo was supplied I’d shoot several thousand rounds in testing. None of us can really afford to drop that kind of money for one review.

  • Joshua

    So they hype their product and then go and make flat cuts on the carrier?

    While it has no effect on anything, not,fully rounding between the carrier rails is a cost cutting measure, not something I expected with how hyped up their machining skills were.

    • Renegade

      So it’s an aesthetic choice on an internal part?

      • Joshua

        Like I said it has no effect on amything, but to sit there and hype their swiss machines as better than the industry standard and then take cost cutting measires on the carrier is kinda strange.

        Sure it is just aesthetic, but it is done to reduce costs whe making the carrier because it allows less time per carrier being machined.

        • kagami

          Yea, and it also lightens the BCG a measureable amount in addition to reducing friction points inside the upper receiver.

          Salient Arms International, WMD, PWS, Adams Arms, and S&W’s Piston gun ALL have angled carrier walls. I’m sure these aren’t very high end vendors either seeing as how they’re just cutting costs.

          • BoHeck

            The weight difference is negligible. It really is to save from buying the form cutter to do the round cuts. Instead the carrier is simply rotated and side milled with a standard end mill. Saves lots of money with no change in performance. It’s a smart move from a manufacturing standpoint. Some people like it, some don’t.

          • Joshua

            Exactly, Honestly it matters not if one does it. My point was, to make this post bragging about their machines, and how they are better than most in the business and then to choose cost cutting measures is kinda strange.

            Really I don’t care about the round vs flat of the carrer, but lets not brag about how awesome their machines are, and how they have better machines than most in the firearms business, and how most people buy from them while they are sitting there with cost cutting measures on their carrier.

          • I don’t know that it is a cost cutting measure. I’d rather think they have a reason for making them in that way.

          • Joshua

            It is a cost cutting measure though, BoHeck lined it out perfectly.

            Now there is absolutely nothing wrong with it, because it’s purely cosmetic. I just like to call a spade a spade and that is all it is.

      • Yes–it has no effect on performance.

  • iHAL

    Looks like a decent carrier but your focus on the company confuses me. You use every possible important buzzword (e.g. “American made” and “veteran owned”) to describe the small company but your understanding of their explanation of their product seems minimal. Are you selling their product or reviewing it?

    To add, I’ve been noticing the number of grammatical mistakes growing on this website throughout the past year and I’m really tempted to just stop reading this blog because I can see the amount of effort put in dwindling every day. What has been going on?

    • A good number of readers want an American made product. I care if it’s veteran owned. If I can buy from a veteran owned business I will. Reviewing it obviously.

      We’ve covered this beat a dead horse subject. I’m proofing and editing all post. It’s no longer an issue.

      • iHAL

        Then stop missing obvious mistakes.

        “I gave them a call and talked with Jason one of the owners.”

        Can you tell me what’s wrong with this sentence?

        Also, the fact that a review was shoved out the door packed with buzzwords in under 500 rounds is troubling to say the least. I’m sorry, but veteran or former LEO owned doesn’t mean much. American made is nice but is by no means a selling point over other products. Trying to explain a manufacturing process you don’t seem to understand is really sad to see. I’ve seen it on both sides of the counter and all it does is turn people with experience in what the speaker is talking about away.

        Honestly, this straight up feels like an ad more than a review. Welcome to the big time print gun publication business I guess.

  • MP

    It’s like the author has read gun magazines his whole life and believes that is a writing style to be emulated. I don’t think this is an ad (though it reads like one), an ad would have less hearsay, more fact and less buzzwords.

    • Fine and who do you write for that makes you an expert. Nope don’t read gun magazines. If you want to talk about the topic fine if you want to take potshots at me use my email.

      • MP

        I’d rather comment publicly on your publicly posted piece. It’s more public that way. I make no claim of being an expert, however reading things from “many sources” (see what I did there?) it becomes quite clear that you could benefit by having your writing reviewed by someone less interested in guns and more interested in decent writing. Seriously, I don’t hate you but your writing is painful.