The Infamous Mil-Spec Standard

Every group has a vocal cadre that demand compliance to their closely held beliefs as defined by their collective.  In the AR-15 realm we have the mil-spec advocates.   These folks have their short list of approved manufacturers and the moment a new company dares to come into existence they pounce to question every minute detail about the materials and processes used to manufacture the interlopers new wares.

mil spec buffer tube

The differences between a mil-spec buffer tube and a commercial buffer tube.

Often times the criticisms leveled against the manufacturers’ products will be centered on compliance to military specifications.  Ironically, most who cite the military specifications for rifles such as the AR15/M16 have never read the actual specifications nor even know where to find them.  They instead resort to parroting what they’ve read on Internet discussion forums.

What are military specifications (mil-spec)?  Simple, they’re standards established by the General Accountability Office (GAO) for defining essential technical requirements of purchased materiel for the military or for substantially modified commercial items to be used by the military.  These standards have been established to guarantee interoperability, commonality, reliability and cost of ownership to ease the strain on logistics systems.

What mil-specs aren’t are a guarantee the product defined is the absolute best that it can be in terms of materials used or processes used for manufacturing.  In the case of the AR15/M16 many of the specifications were established in the 1960’s and 1970’s long before various alloys were developed or even before CNC machining was in common use.

Take the buffer tube (receiver extension) of the AR15 rifle as an example. The military standard tube will have a diameter of 1.148”. The commercial buffer tube will have a diameter of 1.168”. The threads will be slightly smaller in diameter on the commercial tube (1.170’ vs 1.185”) as well. Some commercial tubes will have welded end caps where mil-spec tubes will consist of one piece.

Is the thinner mil-spec tube stronger than the thicker commercial tube? I guess that depends on what tests are conducted. In a real world application would a commercial tube be any more likely to fail if exposed to the same stresses as a mil-spec tube? Everything I can find would indicate no, the mil-spec tube isn’t necessarily more durable or able to withstand significantly more stress than the commercial variant.

staked m4 castle nut

Here you can see the mil-spec staking of the AR15’s castle nut.

So why do we have mil-spec on buffer tubes? Simple. If we go back to the definition of what mil-spec is we’ll find in this case it has to do with interoperability and compatibility. A Soldier should be able to remove a buttstock from one M4A1 and drop it onto another M4A1 without having to worry about compatibility. That’s it.

Another example would be the use of Carpenters 158 steel in the construction of AR15/M16 bolts. Carpenters 158 is the mil-spec standard material for manufacturing a bolt, but is it the best material available? Lewis Tool & Machine (LMT) thinks that Aermet is vastly superior (2.5 times stronger) to Carpenters 158. Their Enhanced Bolt, which is designed to remedy failures associated with the mil-spec standard M16 bolt, seems to be a popular item. This goes back to the specifications written for the M16 being drafted in the 1960’s and 1970’s. Better materials now exist yet the mil-spec standards haven’t been modified.

All the mil-spec advocates will claim the use of Carpenters 158 is a must. They’ll cite the infamous “Chart” hosted by as their holy scripture on the subject, yet in reality Carpenters 158 is a minimum standard and nothing more.

If you’re new to AR15’s and don’t know what to look for when buying a rifle from one of the 50+ makers of AR’s out there today, stick with mil-spec standards to get started. Or, do your research and find out where deviating from the military specifications can be a good thing.

There are some specifications you don’t want to deviate too far from such as MP/HP testing of bolts and barrels that assure quality and durability. Staked nuts on the gas key are a good thing as well. Having .154” diameter pins for the fire control group is another good thing (Colt used larger holes at one time). M4 feed ramps on a carbine are a bonus as they improve feeding reliability.

I don’t completely discount military specifications for the AR15 or think they’re totally irrelevant to the civilian legal AR15. What I do believe is that they’re a bare minimum standard for quality and interchangeability and nothing more.


MAC is an avid shooter, former MCSF Marine, NRA member, Oath Keeper and is commissioned as a Colonel by the Governor of Kentucky. Known for his videos on the Military Arms Channel, he also writes for The Bang Switch, for Shotgun News (Be Ready!) and freelances for Guns & Ammo. MAC has been a life long shooter who has an interest in all things that go "bang" but gravitates towards military type firearms.

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  • Jason A. Partridge

    You dare to question the all mighty MILSPEC!!!! LOL, this is why I like the AK/VZ.58 platform, the only “spec” was for them to work all the friggin’ time!


    I’ve had non mil-spec parts ware mush faster then mil-spec part that where in my Colt. The other companies parts seemed to be a softer steal. The bolt and carrier was wearing faster and showed a fine metallic grit that the Colt did not.

    • Aaron(Elementlmage)

      Anecdotal Evidence combined with False Equivilency.

      Not all, non-milspec rifles/parts/manufacturers are created equal, and that is the advantage of mil-spec, true. But, that doesn’t mean ever non-milspec rifle is a piece of crap like the one you bought. I guarantee there are non-milspec rifles out there that will FAR exceed the quality of any mil-spec rifle, just like there will be some lemons.

      • Josh Duke

        Posted at the same time, Aaron. LOL

      • Lunkhead

        Which rifles? Care to name a few?

    • Josh Duke

      You seemed to have missed the point of the article. MILSPEC is a minimum standard that is 40-50+ years old WRT to the AR/M16 platform. These days, there is a lot of non-MILSPEC stuff that is much better than MILSPEC, and a lot of stuff that ISN’T better than MILSPEC. Seems your bolt was inferior in either materials, manufacture, or both. While a properly made MILSPEC bolt would be better, a properly made commercial bolt with superior materials would be head and shoulders above the MILSPEC bolt in quality.

      Just because your non-MILSPEC bolt was a piece of shit, doesn’t mean all non-MILSPEC bolts (or other parts) are also pieces of shit. :-)

      • Dialn911

        I’m afraid this concept is above the heads of many.

  • Snake

    Mil-spec shmil-spec. If it’s ones buffer tube who cares, now if it’s a BCG well, I want the best. Back to buffer tubes, if one has the angled rear or six instead of four positions this doesn’t mean it’s mil-spec or not. The only way to know for sure it to measure, I found this out the hard way. My tube had all the mil-spec characteristics except for the most important one, the actual measurement, so be sure to always measure.

  • RPM509

    Mil-Spec should be called Min-Spec for minimum acceptable standards to get the job done.
    Trying to educate die-hard’s on what the Mil-Spec stamp doesn’t do is like talking to a brick wall. Timely article, hopefully this will get through to some people (we know it won’t, but we can hope right?)

    • Michael

      If milspec is the minimum then anything less than milspec is less than the minimum and shouldnt be used.

  • Axel

    Didn’t read through the article this time. But MY personal experience w/ the “mil-spec” def. is that, mil. spec doesn’t necessarily the part(s) are top of the line, it just means that that part(s) are combat effective in MILITARY standard, hence milspec, virtually if it works to the minimum it’s combat effective. If it is accurate up to 500m it’s milspec that doesn’t necessarily mean it will be accurate well beyond 500m… just my 2 cents.

  • Terry Zach

    This article is dead on. Mil-spec is a QA standard nothing more. Mil-spec also closely ties to “capable of being built by the lowest bidder”. I work in the government, quite often FOR the lowest bidder. That’s rarely a good thing.

    • killerasteroid

      You are mistaken. Mil spec costs more than commercial and no troop in the field thinks mil spec is anything but top notch. How do you think mil spec was developed for rifles??? They set the spec, tested in lab and field conditions and reiterated the design until they got a weapon that would survive battlefield conditions. What you and others on this post fail to realize is that mil spec is backed up by this iterative process that entailed actual troop usage and lab testing of the weapon. Did Daniels or others claiming to be better than mil spec actually test in these battlefield environments? Doubtful, but if I am wrong, please tell me what wars other manufacturers AR’s have been involved in and which have been tested against these and other extreme laboratory conditions. List is pretty short. One is “Colt”. What are the other?

  • Ron James

    It’s funny that the same people who demand mi-spec, will add every aftermarket part they can find to their rifle because it ‘upgrades’ their weapons.

  • Joe McD

    Here is the the thing. MIL-SPEC is a civilian term. Maybe its more easily understood by the layman. However I prefer the correct term “Technical Data Package” (TDP). As others have said, the TDP is merely a base line. For reliability, a manufacturer should at least meet it. If they can’t meet the bare minimum then why consider them? As the article states, some parts of the TDP could stand to be updated to reflect modern materials and manufacturing processes. Fat chance though with government inertia and all that. Some manufactures have decided to do that on their own. Kudos to them. Just provide the data to back up the claim that XYZ is better than ABC as specified in the TDP.

  • Jay

    As an engineer, here are my $0.02. Mil-spec is important for mechanical dimensions when buying from multiple manufacturers. The mechanical tolerances will likely be looser than necessary to ensure dimensional compatibility. It is also important when specifying the minimum / maximum strengths for certain materials. Sometimes you don’t want too hard or too rigid.

    If you are buying all parts from one vendor, then you can deviate from mil-spec to achieve a tight tolerance fit. For AR rifles, I would stick to mil-spec for dimensional items simply because they guarantee interchangeability.

  • Drmaudio

    Thanks and well said. Mill spec is not without value, but is only important as a minimum standard. Deviating from measurements is potentially an issue in fitment, but is not
    bad if you do your homework.

    • killerasteroid

      You confuse mil spec with minimum as applies to the commercial world. Mil spec ensures that it will last in real world battfield conditions because that’s how and where it was tested. So if you must persist in equating mil spec with “minimum”, then yes, it is the minimum that will ensure survivability in battle conditions which FAR FAR exceeds other manufacturers unproven claims. I was in the military for 20 years and can tell you emphatically that no troops, anywhere, equate mil spec with your version of “minimum”. Mil spec rifles cost more because you get more along with the knowledge that it has been tested to very high lab and battfield conditions.

      There is only one other manufacturer (FN I think) that first fires its weapons and then tests EACH barrel and bolt using HP and MPI technology. Others do batch testing so when you get one of their rifles your bolt and barrel are HIGHLY likely to NOT have been inspected in this manner. And even if it was, they inspect before firing. Colt inspects AFTER firing to ensure it really passed after having been used. And that’s just the bolt and barrel.

      PS if you really believe that mil spec is only important as a minimum standard, then you have eliminated virtually all AR weapons except for Colt and maybe one or two others because very very few AR’s meet mil spec. Comments??

  • ceejoe

    Yes, sometimes “mil-spec” isn’t as good as other options. Melonited vs chrome lined for barrel lining. Parkerized vs nickel boron for bolts, carriers etc. Single stage vs two stage, vs national match, vs drop in triggers. The excellent “mil-spec” plastic handguard. Carpenter 158 vs other bolt materials, A2 birdcage vs whatever other cool flash hider/comp you want.

    However, I draw the line with the receiver extension. Mil-Spec hatred concerning buffer tubes is misguided. Mil-Spec vs commercial is much, much more than a dimensional difference.

    1. Mil Spec tubes have dry film lubricant applied internally. Whats the benefit here? Well, there’s quite a bit of stuff moving around in that receiver extension. A nice semi-permanent lube is a good thing. Lets put it there. Most commercial and “mil-spec” diameter tubes leave out the film.

    2. Mil-Spec tubes are made out 7075 aluminum (approximately twice as strong as 6061 – what most commercial tubes are made of), Hey – extra strong! that’s a good thing, right?
    (Note: many “mil-spec” diameter tubes are NOT 7075. They are 6061. caveat emptor)

    3. Mil spec tubes have “rolled” threads as opposed to “cut” threads. The threads are pushed into position, rather than having material removed to form the threads. Two things here:
    3.1: Rolled threads are “work hardened” so the stronger material just got harder, and less prone to deformation. NOTE:, i’ve torn up the weaker threads on a 6061 tube more than once when tightening the castle nut on said tube. The receiver end plate mangled the threads as I tightened the nut. Had to toss that tube out after that number. Never had this issue with my 7075 tubes.
    3.2: The cut threads on a commercial tube did away with any gains in perceived thickness of material. The outer diameter of the thinnest (weakest!) point is the same distance from the inner diameter as a true Mil-spec carrier. On a commercial tube, there’s weaker material at the weakest point.

    Finally, I’m not sure why you feel the need to point out “mil spec” staking, it’s a very simple, quick and effective means to prevent the castle nut from backing off, and is every bit as reliable (and easy to undo!) as blue locktite.

    Personally, I feel that the extra 10-15 dollars it costs to get the 7075 mil-spec tube is worth it. Hey, the more you know.

    • Michael

      Milspec is proven,prove that the other materials are better.

  • Ragsdale0509

    I own a Colt LE6920, which is as close to “milspec” as it gets without the rock-n-roll switch. However, my next rifle will be a Daniel Defense, which is not milspec. In many ways, Daniel Defense and other manufacturers are making rifles better than a Colt or milspec rifle. For example, a Melonite/nitride treated cold hammer forged barrel is superior to a milspec barrel. As another example, if you’re using a 16″ barrel, a mid length gas system is superior to a milspec carbine length gas system. As another example, a 1/9 twist barrel might be more appropriate for the bullets you plan to shoot than the milspec 1/7 twist barrel.

    Rather than focus on milspec, it’s better to look at the individual requirements of the milspec and decide if those individual requirements are what you want in a rifle.

    • MAC

      You are absolutely correct. Rifles like Daniels Defense exceed mil-spec standards and are superior rifles to the Colt.

      • Blackdog714

        Which is EXACTLY why the people who argue MIL-Spec haven’t a clue of what they are actually arguing… Someone said it earlier, whenever you read MIL-Spec, you should automatically replace it in your head with MIN-Spec (as in MINIMUM Specifications). The example of DD vs. Colt is perfect in that it shows the minimum you should trust your life with and then the upgraded version of the same. I love it when someone argues that their sub-MIL-Spec rifle is “Just as good” or “has NEVER failed them…” as proof that the “MIL-Spec is MIN-Spec” are just fanbois. They get emotionally and monetarily invested and will never admit that spending the $200 more would have gotten them a better rifle. Of course when you only shoot 100 rounds a year, I guess a RRA will be just fine…

        • Michael

          You are quite right.Milspec rifles fail much less than non milspec.Fan bois who dont have milspec rifles and paid as much or more for non milspec are the ones claiming milspec means nothing.If they put 1000s of rounds down range they would most likely see failures.

        • killerasteroid

          Another teachable moment: Mil spec may in your mind mean “min” but it is really “minimum” specs that will ensure the rifle survives real world wartime conditions, conditions under which many other rifles would s h i t the bed. You confuse wartime “minimum” with commercial “minimum”. Also, along with these min-specs as you call them comes the ability to pass some of the most extreme testing conditions that also accompany mil specs. A mil spec rifle is sent to the troops for real-world battlefield testing along with having to meet stringent lab testing. When you meet the mil spec requirement for tolerances and materials, you have a high degree of certainty that you will also meet these or similar battlefield and laboratory testing requirements. As a 20 yr military member I can attest that mil-spec means a very high level product that usually costs a lot more than commercial spec items. The reason for this is because along with mil-spec comes a certainty that it also meets very high reliability requirements. Troops know this and do not view mil spec to mean “minimum standard”. On the contrary, mil spec costs a LOT more to get and troops recognize this and appreciate it.

          Bottom line: mil-spec is a very high level of standard that puts most commercial standards to shame. It also guarantees that the produce and spec itself was the result of rigorous battlefield condition and laboratory testing. Class is over.

      • Michael

        How do you know they exceed milspec?those same companys are trying to be as close to milspec as possible.Superior how do you know?Facts not opinion.

      • killerasteroid

        Only the Colts mil specs have been tested and proven in battle for decades. You can change a barrel coating but unless and until you test it in battlefield type conditions, you are talking out of your a s s. The mil spec that backs up a Colt is the result of decades of proof testing and real world battlefield environments. What wars did Daniels AR’s fight in???? Class dismissed.

    • Michael

      How do you know those other brands are better than colt?Those other brands cant follow the TDP but they claim to be milspec.Melonite is better than chrome? Prove it.Colt is proven in battle not on the internet.

  • mike2588

    Now you need to write an article on what makes the Blackhawk holster on the shelf at Cabela’s “Spec-Ops”

  • John Kubiak

    Old G.I. humorous definition of Mil-Spec…. Measured with a micrometer, Cut with an axe, Beat to fit, Painted to match.

  • BD05

    I think Mil-spec tends to scare people who doesn’t understand or find irrelevant all this stuff.
    Accuracy doesn’t get along with shapes.
    Maybe all video games like CoD, Battlefield, etc…are the vector that’s bring people a twisted picture of guns and their end use.

  • J

    Great video on the new AK from Arsenal. It was interesting to see the groups open up from rounds 1 – 5 to rounds 16 – 20.

    Now, on the subject of “mil spec,” how about testing a mil spec M4 (a decent quality one), and seeing if the same phenomenon occurs? I have done a lot of shooting with M4-pattern carbines and HBARs and have not seen anything like what happened in your SAM7SF review.

  • Zach Billings

    Great article. I’ve actually just started doing heavy research on building my first AR-15, so this was good timing. I’ve been of the opinion for a long time that mil-spec means nothing but “cheapest version that will function adequately”. More articles on what to know about an AR-15 build would be great.

    • Michael

      Milspec isnt the cheapest that will function adequately,it is( what)will function in the heat of battle.If you think milspec means nothing then bet your life on non milspec in a fire fight.

    • Michael

      If milspec means the cheapest,than if you buy less than milspec then you got less than the cheapest.If they cost the same get milspec.

    • killerasteroid

      A teachable moment: Colt makes the LE6920 which is pretty much mil spec. Do you relly want us to believe your “I’ve been of the opinion for a long time that mi spec means nothing but the cheapest version that will function adequately” when Colt is only one of two companies that first test fire their weapons and then do HB and MPI testig after firing and that this process is done on EVERY bolt and barrel?? Are you also aware that the others only batch test bolts and barrels and then test fire it? This means that, say, 1 in 50 that is batch tested might get by but that some others in that batch might have failed if they were tested? Also, their testing is done before firing. How about M4 feed ramps? Colt has these. How about a 4150 vs 4140 barrel? Colt uses the better 4150. Colt also has the 1/7 twist to stabilize heavier loads.How about the mil spec buffer that has internal lubrication? The point is that mil spec has gotten tens of thousands of mil spec weapons through hell and back on the battlefield, thus pretty much negating your opinion that its “nothing but the cheapest version that will function adequately. If it’s minimum in any way its minimum that gets it through real life war time conditions which is a hell of a lot better tham almost any other companies weapons.

  • Pingback: So When is Mil-Spec not Mil-Spec??? - SIG Talk()

  • McThag

    When someone cites the mil-spec demand to know what spec!

    I downloaded MIL-C-70699A. It really doesn’t say much about materials, it’s more of a testing procedure to determine if a given M4 passes inspection for acceptance.

    It refers to a rather large list of other Mil-Specs and Colt’s drawings and TDP. Without those drawings the entire collection of the actual mil-specs gets you almost nothing towards determining if your gun meets it.

    Colt itself is a source describing the limitations on the mil-spec. The extractor spring was known to be a problem for a very long time and Colt had an improved version, but it wasn’t spec so they couldn’t supply it.

  • T C

    Old article. Just ordered a BCM carbine buffer tube it arrived and a colt carbine buffer tube. The colt is .2 oz over the BCM. They are both ‘mil-spec’. Do the math……..

  • Surly Old Armorer

    This entire essay ignores the simple reality that most “non-milspec” AR parts are NOT made of better materials. Most of the non-milspec stuff is simply garbage churned out in China and not even fit for use on an airsoft toy. Commercial buffer tubes DO break, far more often than milspec ones. And not just because the size is different, or the threads are different, but because they’re made out of crappy alloys — 6061 or cheaper — churned out as quickly as possible for sale to mouthbreathers more interested in playing with their rifles as if they were Baries than with actually shooting them.

    Milspec doesn’t mean “best” but it does mean “good enough.”