American Built Arms Company Mission Critical Kit (MCK)

American Built Arms Company has put together a nifty little kit. Some of the stuff I’m not entire sure about (like the black gear bands), but the rest of the items are things I normally try and carry with me when I hit the range. It would be nice if it was small enough to fit inside a grip but still pretty small.

The A*B Arms Mission Critical Kit (MCK) is a collection of critical replacement parts for you and your AR-15/M-4 that are there to serve you in your time of need. The MCK is manufactured for military and law enforcement, as well as civilian firearms enthusiasts. The MCK will make sure you have what you need, when you need it.

The Mission Critical Kit includes the following items:

  • One A*B Arms Complete Nickel Boron Coated Bolt Assembly
  • One A*B Arms Firing Pin
  • One Firing Pin Retaining Pin
  • One A*B Arms Extractor
  • One Extractor Axle
  • Six Gas Rings
  • One Bolt Assembly Instruction Card
  • Two UV Resistant Black Gear Bands
  • One A*B Arms Latex Barrel Cover
  • One 5.56 Broken Shell Extractor
  • Two vials of 3ml Breakthrough Battle Born High-Purity Oil
  • Two Latex-Free Adhesive Bandages and Alcohol Prep Pad
  • One Tactical Black, Ballistic Nylon Case with Multiple Gear Pockets (5″x 3.5″x 1″)

What kind of kit do you carry?

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Tom is a former Navy Corpsman that spent some time bumbling around the deserts of Iraq with a Marine Recon unit, kicking in tent flaps and harassing sheep. Prior to that he was a paramedic somewhere in DFW, also doing some Executive Protection work between shifts. Now that those exciting days are behind him, he has embraced his inner “Warrior Hippie” and assaults 14er in his sandals and beard, or engages in rucking adventure challenges while consuming craft beer. To fund these adventures, he writes medical software and builds websites and mobile apps. His latest venture is as one of the founders of; a search engine for all things gun related. He hopes that his posts will help you find solid gear that will survive whatever you can throw at it–he is known (in certain circles) for his curse…ahem, ability…to find the breaking point of anything.


  • Jason

    I’ve seen those broken shell extractors on the market for years and years, but I’ve never actually seen a broken shell In the tens (hundreds?) Of thousands of rounds i’ve seen fired from the AR system.

    How common is this problem? I always though it was a holdover from Vietnam-era ammunition.

    • JumpIf NotZero

      I had it one single time shooting some really clown-quality ammo that I shouldn’t have been using 🙂

      The issue is the same as the rest of this kit. If you really need to use anything just go to a different gun.

      • Kivaari

        Or keep parts close by. I’ve replaced extractors, ext. pins, and gas rings. On very well used m16s and ARs.

    • It happens. Nothing ruins your day like a stuck case!

      • iksnilol

        I have also never seen a stuck case in person. But I have seen a slamfiring bolt action rifle and have caused a stovepipe with a bolt action.

        • Pretty common malfunction, especially in loose military chambers like belt fed stuff.

          • iksnilol

            I would add that I use either high-end competition guns or inexpensive guns intended for fighting (AKs, MP40s, MP5s, etc.). And a stuck case is still unseen for me. Though I don’t use belt feds. They are way too hot for me + expensive.

          • Kivaari

            It must have been common with the M1873+ US Army carbines. My original has a rod and BSE in the butt stock trap.

        • Doc Rader

          Saw a round actually jam in a SCAR not too long ago… Figure that one out… 🙂

    • Kivaari

      I had dozens of them in Mini 14s and AR15s. It was always with commercial reloads (HSM). I only had a few hundred rounds, and before I even went to shoot it, I had bought 3 BSEs, One for me and one for each kid. They each had Mini14GB, as I did also, but I prefer the AR. Once we had one case fail, I showed them how to use the BSE. Then we just shot all of that ammo with around 25% failing. None of those rifles had failed with any ammo before or after that incident.. You can run across it else where. I’ve seen quite a few in hunting rifles as well. Almost all of them with reloads or very old military ammo.

  • JumpIf NotZero

    “The MCK will make sure you have what you need, when you need it.”

    No. I don’t think it will. Because if I break a bolt / firing pin / gas rings etc, and need a new one right away. In what definition of “need” are you going to have the time to place AR-15 mechanic and disassemble and reassemble the bcg?

    No. Just carry a spare bcg if you think you might “need” it. This entire kit is irrelevant to 99.5% of anyone’s actual uses. If I’m going to go to a carbine event or class, I just bring a spare bcg and maybe a spare carbine depending on how I’m packing.

    If you’re going to carry something you’d almost certainly never use, dear lord, please carry an IFAK… And I’m sure it would be asking too much to learn how to use one, but whatever.

    • Core

      I disagree. You should use your original bolt if at all possible, and you can check your replacement bolt headspace prior to returning it to service if you instal the new bolt. I don’t see the need to replace the carrier unless its damaged and that rarely happens. You can lube the bolt and slide it in replace the cam pin, firig pin, and firing pin retaining pin. I have a spare bcg but Im not going to carry it around with me when I can carry a spare bolt and field pack. Windham Weaponry sells a nice field repair kit all ready to go. I think A*B Arms has a nice little kit, but I would want to drop in the rest of a field repair kit to round it off. I wonder if the barrel cover comes in MARPAT?

      • Ben Bushong

        I think the point is spending the time to disassemble the BCG to fix the broken parts NOW. When will it fail? When you NEED it NOW. IF one is worried about their bolt, gas rings, etc, failing, they should just carry an entire BCG and fix the broken one at their leisure after the event that requires the need.

  • iksnilol

    How often do you break your bolt? I constantly see people carrying spare bolt assemblies or complete BCGs. Is it really that big of a problem?

    • Yep. Patrick R had an issue this last weekend. Luckily he had a spare bolt in his grip!

      • Limonata

        Its not that it does not happen, the question is how often? I have a Stag Arms 3g and while I do not even make believe I am a pro, over 3years and 15 3 gun evens with thousands of rounds including practice at various local events, I have had issues but not a broken bolt. While I carry everything I need just in case because I would hate to have a bad day, the bolt seems to be the least of my worries thus far. My biggest problem thus far has been broken optics including a Burris scope that kept loosing zero during completion, a spring and magazine issues until I switched to Lancer L5s. While this guy behind the gun has had issues, I find it hard to blame the gun or bolt.

        • Doc Rader

          I would assert that a broken extractor would be a more common issue, and at a match, say, just chucking a replace BCG in is faster and more expedient than rebuilding it in the “field”. 2 is one, and 1 is none…

          Save the rebuild for the workbench at home…

          The utility of the kit is a grab’n’go (something you can just chuck in the range bag and forget about until you need it). That was my main thought, anyway.

    • I recently started having failure-to-eject problems. I suspect that the ejector spring is bad, as the extractor spring seems okay. Have not had time to fully troubleshoot or fix the problem bolt yet.

  • Lacquered red plywood

    I think there’s a similar kit for the AK platform. If you open it up you see no other contents besides a photo of Mikhail with a very concerned/angry look on his face, and a cartoonish text bubble that reads “are you f****** kidding me?”

    • Sam Schifo

      Don’t forget a bottle of vodka.

    • Grindstone50k

      No, the text reads “Rifle is fine.”

  • SlippedThroughTheCracks

    Well into the 21st century, any company that doesn’t create or maintain a website with up-to-date product information doesn’t deserve to be “liked” on facebook or anywhere else.

  • Southpaw89

    Seems like an even simpler kit could be marketed to hunters, just some solvent, oil, a stiff nylon brush and a microfiber cloth could be very useful in the field, may just make one myself now.