Issue 19 Guide to Super-Light AR-15 Bolt Carrier Groups Steven Kuo 2 Comments, Join the Conversation Feather-Weight for the Win The AR-15 platform has arguably become one of the most finely tuned weapons ever to go bang. Its ubiquity, modularity, and open architecture have resulted in a veritable cornucopia of modifications and accessories designed to optimize it for a wide variety of applications. Everyone from large established players to guys in their garage workshops with a good idea have conceived, produced, and marketed almost anything that you could imagine — including the topic of this article, lightweight bolt carrier groups (BCGs). From machining lightening cuts to using space-age materials, these featherweight BCGs reduce the reciprocating weight in your AR-15, resulting in smoother operation and reduced felt recoil and muzzle movement — allowing you to get more hits in less time and to keep your eyes and optic on target throughout. Direct Gas Impingement 101 At its core, the AR-15 platform is a gas-operated semi-automatic rifle, specifically a direct gas impingement system. Press the trigger and the hammer is released, striking the firing pin. The firing pin ignites the primer of the chambered round, in turn igniting the powder and sending the bullet on its merry way down the barrel. As the bullet travels down the bore, it passes by a small gas port. As this happens, gas hurtles into the gas port, through the gas block and back down the gas tube, toward the shooter. The rearmost end of the gas tube is seated in the gas key of the bolt carrier group, so the gas continues into the interior of the bolt carrier (this is where the tail of the bolt assembly with its gas rings sits, hence all the fouling that builds up there) and pushes it rearward, cycling the action. When moving rearward, the bolt carrier group pushes against the buffer and action spring contained within the receiver extension. The spring compresses sufficiently for the bolt to travel far enough back to extract and eject the spent cartridge and then strip and chamber a new round from the magazine (or alternately, lock back if empty). This intricate dance is dependent on a number of factors to ensure reliable operation under varying conditions. The ammunition you're shooting might be hot military rounds, weaker commercial loads, or even custom hand-loaded mouse fart competition loads. The relation of the length of the gas system (e.g. carbine, mid, intermediate, and rifle) to the overall length of the barrel determines how long the bullet remains in the barrel after it passes the gas port and affects how much gas is routed back into the action — as does the size of the gas port itself. The combination of the bolt carrier group and buffer reciprocating against the action spring is also important. Some complain that the AR-15 platform poops where it eats, but you still have to appreciate the ingenuity of Stoner's in-line design. Tuning the Gun For applications where your life depends on your weapon, you would emphasize maximum reliability — so the mix of all of the components listed above needs to work no matter what type of ammo and what sort of conditions. This could be hot military loads in the blazing desert, or weak imported commercial ammo in the freezing cold with a disgustingly fouled gun. The solution for this is typically plenty of gas and heavier components — the gun will kick more, but that's not the highest priority in this case. Plus, work on your technique and you can enhance your recoil management. But we're Americans, and we can't resist tuning things to optimize their performance, whether cars or guns. And when you have narrower operating parameters — known ammo, known range of conditions — you can do this with your AR-15 and still leave yourself with extra margin. Because even if you're just shooting paper and steel for bragging rights or a prize table, you still want to win and a malfunction could be catastrophic to your rankings or ego. Generally speaking you want to tune your rifle to operate reliably with the weakest ammo and coldest conditions that you expect to encounter. Since the BCG (along with the buffer) comprises the mass that reciprocates from shot to shot, they affect felt recoil and muzzle rise. Reducing that mass — and also the gas operating the action — will dampen the first recoil impulse when the BCG and buffer hit the rear of the receiver extension as well as the secondary impulse when the BCG goes back into battery. Utilizing your desired combination of adjustable gas block (or gas key), gas port size, gas system length, and ammunition, along with a lightweight BCG (and buffer), you can tune your rifle to consistently feed new rounds and lock back on empty. Standard buffers typically weigh from 3 to 5 ounces, while our baseline Mil-spec BCM bolt carrier group weighed 11.6 ounces — a lot to work with. Sure enough, the lightest BCG we tested clocked in at a feathery 5.74 ounces. Materials, Finishes, and Testing Steel: Many companies machine material away from the tried-and-true steel bolt carrier design to reduce weight. Some are more extensive than others, and the lightest are not able to retain the forward assist feature — some may bemoan this and others will celebrate it. 8620 is almost universally used, except for JP's 416 stainless steel offering. They all boast advanced finishes as well (see Issue 13 for more details on the various coatings and treatments). While some tout that lubrication isn't necessary, we always use plenty of lube and enjoy the peace of mind that comes from the extra lubricity such finishes provide. Titanium: A wonder material used widely in aerospace applications, titanium has the highest strength-to-density ratio of any metallic element, while being highly corrosion resistant. 6AL-4V titanium alloy is used by the companies in this lineup (note Boomfab did not disclose its material choice). Compared to 8620 steel, 6AL-4V is about 40 percent lighter, with comparable yield strength, but lesser ultimate tensile strength. One could question the latter spec, but we'd argue that in the case of a bolt carrier, if it starts to deform it's already time to be concerned. On the negative side, titanium is softer than steel and galls (which is adhesion and friction between two surfaces sliding against one another — sound familiar for a bolt carrier?). To address this, all of the carriers are treated with some sort of surface hardening finish, whether physical vapor deposition, nickel boron, or H&M Metal Processing's brand new process (described later). In any case, you'll find us running titanium carriers even wetter than our steel BCGs. Aluminum: Roughly 40 percent lighter than titanium, but with about the same loss in yield strength, aluminum carriers fall squarely into the realm of “race parts” to achieve the lightest possible recoil impulse. JP Enterprises and Whiskey Arms both advise their products should only be used in competition rifles, not duty or defensive weapons. Their carriers are both hard anodized, bringing aluminum to the approximate equivalent in excess of 60 on the Rockwell C hardness scale. But it's still aluminum underneath, with hardened steel scraping against it every which way. JP's instructions state, “If you don't have oil spraying on your shooting glasses, you need more oil.” Nuff said. Beyond lightening, most also modify the BCG spec, whether increasing or tweaking the bearing surface area (e.g. all but the AIM Surplus, RCA titanium, and Seekins) or changing the gas ports and cam pin path (e.g. Lantac). Gas keys were all aggressively staked to prevent the screws from moving, with the exception of the one-piece Voodoo with integral gas key and the Young Manufacturing (see its website for its carefully explained rationale). All bolts are steel, either C158 or 9310 depending on the company. All are also shot peened to reduce susceptibility to metal fatigue. Testing procedures during manufacture and quality control have gained visibility of late with the consumer market's appreciation for all things Mil-spec. All of these manufacturers perform magnetic particle inspection (MPI) to detect surface cracks. Some companies also high-pressure test (HPT) their bolts, proof testing them under high pressure to check for failure. While some folks have religion about this, we don't — with certified high-quality materials from reputable manufacturers, we sleep soundly at night, knowing that life expectancy will also be longer than those subjected to HPT. Without further ado, here's a wide selection of the best the industry has to offer, from aluminum to titanium to lightened steel carriers. There's bound to be a product that has the exact mix of characteristics and features that you're seeking. The Shot Heard Around Social Media One of the hottest trending topics on social media after the SHOT Show in January this year was the revelation that some unscrupulous character stole Lantac's prototype titanium enhanced bolt carrier group right off the company's display table. Facebook, gun blogs, and online forums were abuzz with shock and outrage — how could it be that in a community with such strong fundamental underpinnings of integrity, personal responsibility, and brotherhood that such a thing would happen? Well, there are bad apples in every bunch, but the industry and the community showed its true colors as it rallied together to the cause. From manufacturers large and small to concerned individuals, offers of rewards for information leading to the return of the stolen item came pouring in. Most had no stake in the game, no business or relationship with Lantac at all — yet they lent their support. In total, there were offers of product, services, and cash exceeding $30,000! We're pleased to report that Lantac's BCG is back in the right hands. In fact, here it is, with the SHOT Show tag still intact! You heard it here first…and the backstory goes like this: Later that same day when the Lantac crew posted the news on their Facebook page and it went viral, they received a strange phone call from an unlisted number. A very nervous fellow stammered his way through the conversation, indicating that “his friend” had “accidentally” taken the BCG home from SHOT Show. Apparently the Lantac titanium BCG is so incredibly lightweight and compact that he didn't even notice he had it in his pocket! Until the next week! He wouldn't give Lantac any further information, so they gave him their address and hung up, figuring it was a lost cause. Lo and behold, several weeks later, a white USPS bubble mailer arrived, containing another white USPS bubble mailer, with the stolen BCG swaddled within. The postage was paid in cash from a post office in Mesa, Arizona. However disappointing that such a thing could happen at a closed industry event, the reaction and support in the aftermath was a shining example of what the firearms community is all about. Mirror, Mirror on the Wall, Who is the Lightest of Them All? Because we're, well, RECOIL and we do OCD shit like this, we obtained a calibrated laboratory scale to precisely measure the bolt carrier groups. For the two products without bolts (the TS Arms and Whiskey Arms), for the sake of comparison we've presented their total weights here with a standard bolt assembly for the former and a bolt assembly with a titanium firing pin for the latter. For our curious detail-oriented readers, a titanium firing pin saves approximately 0.03 ounce of weight. Material Weight Aluminum JP Enterprises 5.74 oz Whiskey Arms 5.86 oz Titanium Boomfab 6.39 oz Rubber City Armory 7.75 oz AIM Surplus 7.80 oz Lantac 8.02 oz Steel AP Customs 8.22 oz JP Enterprises 8.77 oz Rubber City Armory 9.04 oz Young Manufacturing 9.23 oz Voodoo Innovations 9.55 oz TS Arms 9.87 oz Seekins Precision 10.2 oz Spikes Tactical 10.5 oz BCM Mil-spec 11.61 oz Aluminum Bolt Carrier Groups Make: JP Enterprises Model: Ultra LMOS Bolt Carrier Group with JP EnhancedBolt Weight (complete BCG / carrier only): 5.74 / 3.77 ounces Carrier Material and Finish: 7075-T6, anodized Bolt Material, Testing, and Finish: 9310, proprietary, chromium nitride Price: $461 Url: www.jprifles.com Notes: JP Enterprises has long been ahead of the curve, offering complete competition rifle systems with lightened components and adjustable gas before it became trendy. It actually used to sell aluminum BCGs over a decade ago, but stopped because customers weren't maintaining them properly and complaining about premature wear. With lots of prodding to bring them back, JP complied with the lightest BCG on the market. Bearing surfaces on the carrier are substantially larger than standard BCGs. Comes with a titanium firing pin to eliminate potential for slam-fires and a one-piece gas ring. Available with or without JP's EnhancedBolt with radiused bolt lugs. JP Enterprises Ultra BCG $437.99 brownells.com Make: Whiskey Arms Model: LBC-Aluminum Lightweight Bolt Carrier Weight (complete BCG / carrier only): n/a / 3.89 Carrier Material and Finish: 7075-T6, anodized (oil impregnated) Bolt Material, Testing, and Finish: n/a Price: $200 (bolt not included) Url: www.whiskeyarms.com Notes: During the time that JP had discontinued its product, Whiskey Arms' owner longed for a super-light aluminum BCG. So he set out to make his own at the most affordable price point that he could hit. The result is the LBC, offered as a carrier only (with gas key installed) and intended to replace the full-weight carrier on your existing BCG while reusing your bolt. Of course, you can also pair it with a bolt from your favorite provider (it's shown here with a NiB bolt assembly). Bearing surfaces are enlarged with some relief cuts. Note that you lose forward assist capability. Titanium Bolt Carrier Groups Make: AIM Surplus Model: AIM TiX M16 .223/5.56 NiB Bolt Titanium Carrier Group Weight (complete BCG / carrier only): 7.8 / 5.7 ounces Carrier Material and Finish: 6AL-4V, ion-bond Bolt Material, Testing, and Finish: 9310, MPI, Nickel Boron Price: $300 Url: www.aimsurplus.com Notes: The AIM Surplus titanium BCG has a full M-16 carrier profile with the extremely hard and wear-resistant IonBond on the carrier and NiB on the bolt, gas key, and cam pin. If you're looking for Mil-spec with lighter weight, AIM has you covered. It includes an extractor buffer and O-ring. There's no bling or flash here, just top-shelf components. Make: Boomfab Model: Titane Carrier Weight (complete BCG / carrier only): 6.39 / 4.3 ounces Carrier Material and Finish: Proprietary, surface hardened Bolt Material, Testing, and Finish: C158, MPI/HPT, phosphate Price: $579 Url: www.boomfab.com Notes: Cutting edge, with a price to match, Boomfab's offering is the lightest titanium BCG in our guide. The finely machined carrier has increased bearing surfaces and made a splash in the market when they started appearing on the 3-Gun Nation circuit in the hands of professional shooters burning down stages. The company doesn't disclose its material choice or surface hardening process, but reports that its shooters have logged tens of thousands of rounds on its Titane carrier. Boomfab advises to keep the BCG well lubricated. Make: Lantac Model: Titanium Enhanced Bolt Carrier Group Weight (complete BCG / carrier only): 8.02 / 5.92 ounces Carrier Material and Finish: 6AL-4V, Nickel Boron (UCT EXO) Bolt Material, Testing, and Finish: C158, MPI, Nickel Boron (UCT EXO) Price: TBD, expected to be $500-600 Url: www.lantac-usa.com Notes: Late last year, Lantac introduced its steel enhanced BCG, with a host of interesting features such as patented forward-facing gas ports to smooth operation and redirect gas away from the shooter, a flared carrier tail to improve consistency, slightly enlarged bearing surfaces, and a domed cam pin to reduce wear. It then made a titanium prototype for the SHOT Show in January, shown here. Lantac touts the increased lock time of its steel BCG, which is actually slightly heavier than standard, but they received so much positive feedback on the prototype that they're bringing it to market for those who want a lightweight carrier. They intend to start taking orders in May. Make: Rubber City Armory Model: Titanium Complete Bolt Carrier Group with adjustable gas key Weight (complete BCG / carrier only): 7.75 / 5.65 ounces Carrier Material and Finish: 6AL-4V, patented thermal chemical diffusion process Bolt Material, Testing, and Finish: 9310, MPI, Blacknitride+ Price: $320 (estimated) Url: www.rubbercityarmory.com Notes: RCA's sister company, H&M Metal Processing, recently developed a new patented thermal chemical diffusion process to treat titanium and titanium alloys for high-wear applications. Like the company's nitriding process for steel, it's not a coating on top of the substrate material, but rather a treatment affecting the surface of the metal. Intended for aerospace applications, it also found a great application in lightweight BCGs (the prototype is shown here). RCA says it can endure abuse like nobody's business, so we look forward to running it hard. It's available with a standard or adjustable gas key, so you can fine-tune uppers lacking an adjustable gas block. Rubber City Titanium BCG $370.99 brownells.com Steel Bolt Carrier Groups Make: AP Customs Model: Rhino Series 223/5.56 Low Mass Bolt Carrier Weight (complete BCG / carrier only): 8.22 / 6.23 ounces Carrier Material and Finish: 8620, Nickel Boron Bolt Material, Testing, and Finish: 930, MPI/batch HPT, Nickel Boron Price: $305 Url: www.apcustomusa.com Notes: AP Customs wanted to make its BCG as light as possible, even using a titanium firing pin (the only one other than the JP aluminum offering) — not so much for fear of slam-fires, but for the minor weight savings. The lightening cuts are extensive and achieved the goal, posting the lightest weight of the steel BCGs. It also has slightly increased bearing surfaces. You'll lose forward assist functionality though. Note that the firing pin retainer is a solid affair rather than the usual cotter pin, harkening back to the early days of the M16 platform. Make: JP Enterprises Model: LMOS Bolt Carrier Group with JP EnhancedBolt Weight (complete BCG / carrier only): 8.77 / 6.68 ounces Carrier Material and Finish: 416 Stainless steel, polished or QPQ nitrided Bolt Material, Testing, and Finish: 9310, proprietary, Chromium nitride Price: $353 Url: www.jprifles.com Notes: The elder statesman of the group, JP's LMOS system has been a staple for competition shooters for years — and is still the second lightest of all the steel BCGs in this group. The LMOS BCG displays all the maturity and refinement you'd expect from JP. Available in various configurations and for .223, 6.5 Grendel, and .308, it's pictured here with JP's EnhancedBolt. The bearing surfaces are significantly larger than standard, and it's finished in either a beautiful mirror polish or black QPQ nitrided. Make: Rubber City Armory Model: Low Mass complete BCG with adjustable gas key Weight (complete BCG / carrier only): 9.04 / 6.94 ounces Carrier Material and Finish: 8620, Blacknitride+ Bolt Material, Testing, and Finish: 9310, MPI, Blacknitride+ Price: $269 Url: www.rubbercityarmory.com Notes: The third lightest steel carrier in this bunch, the RCA offering features its popular nitride finish and an optional adjustable gas key. Utilizing set screws that protrude into the gas key, you can meter the gas delivery — very handy as a turnkey drop-in system if you want to use an upper that already has a fixed gas block. The bearing surfaces are also slightly larger. Note that the standard gas key on our sample shown above was replaced with the adjustable one and rushed out to us, and it inadvertently wasn't staked before shipment — their production units are all staked. Make: Seekins Precision Model: Low Mass Bolt Carrier Group Weight (complete BCG / carrier only): 10.2 / 8.11 ounces Carrier Material and Finish: 8620, Melonite Bolt Material, Testing, and Finish: 9310, MPI/HPT, phosphate Price: $229 Url: www.seekinsprecision.com Notes: Modestly lightened with ball cuts on the carrier body and additional material removed from the sides, the Seekins BCG is about 1.4 ounces lighter than standard. Otherwise, it's everything you'd expect from a premium aftermarket BCG, including a Melonite finish on the carrier — at the most affordable price point in the bunch. Make: Spikes Tactical Model: Lightweight Nickel Boron HPT/MPI M1 Bolt Carrier Group Weight (complete BCG / carrier only): 10.5 / 8.37 ounces Carrier Material and Finish: 8620, Nickel Boron Bolt Material, Testing, and Finish: C158, MPI/HPT, Nickel boron Price: $250 Url: www.spikestactical.com Notes: Sporting Spike's Tactical distinctive flair, this BCG is perforated with ovals for a modest reduction in weight (it's the heaviest steel BCG in this group). Coated throughout with nickel boron, the BCG is otherwise the same as the company's Mil-spec offerings. It has slightly larger bearing surfaces and comes with an extractor insert and O-ring. Make: TS Arms Model: Low Mass Plasma Coated Bolt Carrier Weight (complete BCG / carrier only): n/a / 7.77 ounces Carrier Material and Finish: 8620, plasma coated Bolt Material, Testing, and Finish: n/a Price: $220 (bolt not included) Url: www.tsarms.com Notes: These BCGs score high on the chicks-dig-it scale, with glossy plasma coatings in bronze, gold, or silver. Who needs an Apple Watch when you can have one of these instead? The model pictured doesn't have forward assist serrations, but a variation with them is available. The bearing surfaces are also significantly enlarged. TS Arms sells the carrier by itself, along with a plasma-coated cam pin. Bolt assemblies can be purchased separately. Make: Voodoo Innovations Model: Lifecoat DI Integral Low Mass Bolt Carrier Group Weight (complete BCG / carrier only): 9.55 / 7.45 ounces Carrier Material and Finish: 8620, Lifecoat (Nickel/PVD) Bolt Material, Testing, and Finish: C158, MPI, Lifecoat (Nickel/PVD) Price: $251 Url: www.voodooinnovations.com Notes: A University of Texas study released this year posited that men are inherently attracted to curvy women due to evolutionary developments. Thus men should love VDI's curvy low mass BCG. It's mid-pack amongst the steel carriers in weight reduction, but stands alone with its integral gas key, eliminating potential gas key issues. The Lifecoat treatment is a combination of a nickel layer plus a physical vapor deposition coating to provide the benefits of lubricity and corrosion resistance along with extremely high surface hardness and wear resistance. The bearing surfaces are also modified with relief cuts. Make: Young Manufacturing Model: SLC Super Light Carrier Complete Weight (complete BCG / carrier only): 9.23 / 7.14 ounces Carrier Material and Finish: 8620, hard chrome Bolt Material, Testing, and Finish: 9310, MPI, hard chrome Price: $265 Url: www.youngmanufacturing.net Notes: Young Manufacturing has been making bolt carriers for a long time — since 1991 — with a variety of offerings from National Match to lightweight models. Its lightweight BCG is about 2.4 ounces lighter than standard. It has enlarged bearing surfaces as well as Young's hallmark hard chrome coating. Hard chrome is not an easy process to accomplish consistently well within budgetary constraints, but the company built its reputation on it. Note that as explained earlier, Young does not stake its gas key screws. 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