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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 junkies.  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 of the materials and processes used to manufacture the interloper’s new wares. Often times the criticisms leveled against the manufacturer’s products will be centered on compliance to military specifications. Ironically, most who cite the military specs for rifles such as the AR15/M16 have never read the actual specifications or even know where to find them. Instead, they 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 a particular product is the absolute best that it can be in terms of materials used, processes for manufacturing, etc. In the case of the AR15/M16 many of the specs were established in the 1960’s and 1970’s long before various modern alloys were developed or even before CNC machining was in common use.

Take the buffer tube (receiver extension) of the AR15 rifle for instance. The military standard tube has a diameter of 1.148”.  A commercial buffer tube has a diameter of 1.168”. The threads are slightly smaller in diameter on the commercial tube (1.170’ vs 1.185”) as well.  Some commercial tubes have welded end caps where mil-spec tubes 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 indicates no, the mil-spec tube isn’t necessarily any more durable or able to withstand significantly more stress than the commercial variant.

So why do we have mil-spec on buffer tubes? Simple. If we go back to the definition of what mil-spec is, 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 is the use of Carpenters 158 steel in the construction of AR15/M16 bolts. This goes back to the specs written for the M16 being drafted in the 1960’s and 1970’s. 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. Better materials exist now, but the mil-spec standards haven’t been modified.

All the mil-spec junkies will rant and rave that Carpenters 158 being a must. They’ll cite the infamous “Chart” hosted by as their holy bible on the subject. Yet in reality, Carpenters 158 is a minimum standard and nothing more.

Here’s how I view military specifications as it relates to the AR15/M16.  It’s a good place to start. Period.

If you’re new to AR15s 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 specs 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, too, as they improve feeding reliability.

Do your homework before making a purchase and you should do just fine when buying a new AR. But please, don’t get too caught up in the whole “if it isn’t mil-spec it isn’t s***” nonsense and avoid becoming one of “them”.

Tim Harmsen runs the Military Arms Channel

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  1. Steels (and other metals) used in weapons (or other) production are only half the story. Telling me that you use “XYZ” steel doesn’t impress me. For example, telling me that you’re going to replace your Garand bolt originally made with “War Department 8620” with Aermet steel… will cause me to give a wry smile – because the steel is only half the issue. The case hardening is the other half.

    Telling me that you use “XYZ” steel and then detailing the heat treatment protocol, with heating times, quenching media, tempering temperatures, soak times, atmospheres used in the furnaces, etc… that starts to impress me. I say “starts,” because then to finish impressing me, you have to detail for me what your testing protocol is, what your sampling protocols are, etc.

    This is the sort of stuff detailed in military specifications. As you correctly point out, the military specs might not result in the best technology or materials available being used in the product. That’s a no-brainer – the military is, after all, seeking to have the lowest cost bidders win on their contract bids.

    When manufactures adhere to “mil-std” this, that or some other thing – if they’re actually adhering to it, there’s a whole lot of manufacturing processes that come along for the ride – not just a materials specification. When a manufacture tells me they’re using some new material, but are still conforming to the testing and sampling protocols for the old material(s), and they’re showing the statistically valid improvements (to a 95% confidence interval) – OK then, let’s run with it. If a manufacture just sub’s some new material and ditches the rest of the production/testing/sampling specifications, and then waves a materials spec sheet in my face? Eh, I’m not so impressed.

    • +1 let’s jump on and read about coatings coming off LMT’s “enhanced” BCG within a few hundred rounds. I love experimental cutting edge materials. Key word being experimental.

  2. I saw one of those charts and I was like “that manufacturer sucks” (for one of the mil-specs) and “I know that is a good builder” (for one of the non-mil-spec, might have even been LMT). YMMV, but I would go by current reputation-noting that although reputation rarely moves quickly in a positive direction it can rapidly move the other way due to mergers/acquisitions or management changes.

  3. Everybody’s an expert, or at least wants to be.

    Does it make a difference? Not really. Just like everything else people have to go with what they’re comfortable with. In the end it isn’t so much what you’ve got as how good you are with it.
    Some stuff might be better than other, but any PGA golfer is still going to blow me away with even the cheapest set of clubs and golfballs no matter what i’m using simply cause I don’t golf.

  4. I think the problem with a lot of also ran AR-15 manufacturers is that they do not meet the specification as a minimum standard, rather than the companies using it as a starting point to be improved upon in areas. That said, many of these guns will still work just fine for most purchasers of AR-15 rifles, as they only shoot a few hundred rounds through them in their lifetime.

  5. This is a great article. I think Mil-Spec standards exist for a reason, but people take it way too far. Just in the last few days I’ve encountered scores of internet experts and gun snobs who felt the need to trash one of my friend’s AR15s that wasn’t a Mil-Spec gun, the fact that his gun runs reliably and shoots straight never really meant anything because his barrel wasn’t 11595 and his bolt wasn’t MP tested in the factory.
    Things like MP/HP testing are great, and I think it’s a good idea to look at manufacturers that test their parts/guns before they leave the factory, but people need to stop being gun snobs about it. It really reminds of the H&K forum (Not the official one) I was a part of for a while, you mention a Glock or anything else that isn’t a USP and you’re bombarded with dozens of gun snobs telling you about how the USP is superior to any other handgun in the world, and Glocks are hand grenades shaped like guns. People do the same thing with ARs, to them if it’s not a Colt, BCM, DD, LMT, or whatever else it’s just going to fail on you.
    Nobody likes a gun snob, not even other gun snobs.

    • I have to agree with you on this one. Depends on what the gun is being used for. If someone’s life depends on it it should meet or exceed a spec based on that evaluation. If it’s a hobby gun I see no reason in saving some money with a lesser grade of albeit still functional firearm. I have alot of gun snob brand stuff but I am not a gun snob and dont like gun snobs either.

      • I hate that most of these guys really think that these high priced big name parts are the best when in my experience I like build my owne can make one that is just as accurate and reliable for half the price if not less if you do your homework witch means you may have to return a few things no big deal unless your always in a rush you can make a dame nice rifle

    • Re: MilSpec. it is important to remember that the spaceshuttle Challenger was built to Milspec and we know what happened there. Gun snobs: most of them haven’t a clue what they are talking about. They depend on what some other (doesn’t) know-it-all told them. For instance, I got into a heated debate over the M1 Garand with one of these self-described “experts.” For one, they claimed it was called a “Grand.” Even after I provided documentation that it was named for it’s designer, John Garand, they insisted that it was a “common mispelling.” Also claimed it was chambered in 7.62×51/.308 and that was the same thing as a 30.06. Sigh. I tried to tell this “expert” he was wrong and he went ballistic. He had no concept of the difference between the .308 and the 30.06 and insisted they were the same thing. (Note: Toward the end of the M1 Garand run, there were some that were chambered in .308)The .308 cartridge didn’t exist till the 50’s while the Garand was designed in the 30’s and sent off to WWII and I gave him the documentation to prove it but he still claimed the “expert” he got his information trumped mine. WOW. Thes guys are all over the internet. If they listen to some numbnutz give them wrong information, then why won’t they listen when someone gives them the right info?

  6. All I can hear in my head is my Drill Instructor telling me that all my equipment “was made by the lowest bidder!” hehe.

    Good points all around. As recent and new AR purchaser I had to wade through quite a bit of info. The only I worry about being mil-spec are generally dimentions, not materials.

    • “The only I worry about being mil-spec are generally dimentions, not materials.”

      This. As I’m new to the black rifle thing, my chief concern is interoperability of the stuff I buy. I ran into a friend of a friend at a gun show, and he was having a mil-spec buffer tube put on his AR by a guy there at the show. He’d previously had a commercial buffer tube and stock, but had gotten a great deal on a really nice mil-spec buttstock. Prior to that day and that conversation, I had no idea there were two different “specs” that were not interchangeable. I don’t want to buy some thingamajig and have it end up not fitting some other doodad I already have.

  7. No AR-15 is truly “mil-spec”, otherwise it would be an M-16. Select Fire. Our military doesn’t use Ar-15s. Having mil-spec bits and pieces on your gun doesn’t make it mil-spec, for the above mentioned reason.

  8. Excellent article. There are basically three types of AR’s: below mil-spec, mil-spec, and above mil-spec. An spaghetti MRE is mil-spec, but clearly inferior to my wife’s spaghetti. An LWRCi, LMT, POF Armory is above mil-spec in overall design and price point.

  9. SLAB RANKLE, you have hit the nail on the head there buddy…… only real mil spec is the M16 and you can get one with the right permit…….

  10. There are a few milspec requirements that are gold. M4 feed ramps and MPI are a must have.

    That being said, anything the military gets are always made by the lowest bidder. So in essence, you’re sticking to requirements met by the lowest bidder. Independent research and testing beat internet dogma any day of the week, and twice on sundays.

    Does that mean that an Olympic Arms AR is as good as a Saber Defense or a Colt? No, not at all. So look at consumer reviews before you buy.

    • the lowest bidder argument does not always apply. Many of the recent contract solicitations have grueling practical field testing that a product has to meet before it gets the stamp…..

      One key counter argument to lowest bidder is the M110 sniper rifle deployment kit and the new MSR contract won by remington…. not even close to the lowest bidders.

    • Good point. While an AR-15 may per “engineering drawings” as far as dimensions, that in itself is no guarantee it is per “military specifications” or “milspec.” You can machine a bolt from aluminum, paint it black, and it is “per engineering drawing” but definetly not milspec. Just because it looks like it real thing doesn’t necessarily mean it is.

  11. Nice article.
    Since most of us are not machinists or gun smiths with 30 years plus under our belts it is all to easy to put faith in something that is a minimum standard for interoperability not the best their is.

  12. I’ve been pushing for the term “industry standard” as a civilian alternative to “mil-spec”.

    While “mil-spec” is a starting point, it is also the absolute bare minimum that the DOD allows for a weapon to be considered combat worthy.

    The fact is, “mil-sepc” as a term is overused by companies that in no way meet those standards, but have a passing aesthetic resemblance to the military issue M4.

    There are companies that don’t meet the minimum basic standards, however most of them are priced up against those that do and are marketed as such. Example, a standard BM or DPMS is often sold at prices approaching a basic Colt 6920 or BCM. Choosing the lower quality yet equally priced gun is foolhardy. However, when looking at something such as a $600 S&W M&P15 Sport compared to the $1050 6920, the value starts to shine and the numbers become slightly less important, especially with the S&W having close (not equal) numbers.

    The fact is, if you want a reliable fighting rifle (as opposed to a weekend range gun that resembles something cool) the brands that tend to emulate “mil-sepc” are universally considered (GTG). Think Colt, BCM, DD, LMT. Others have specs that go above and beyond mil-spec. Think KAC, Noveske, LWRC, LaRue, HK. Then there are “me-too” rifles. Those that charge prices near the “mil-spec” but don’t have the specs or reputation to justify them. Many of those used to be GTG, but in the last decade have reduced quality to increase production and profits, and have also been surpassed by any of the other 143 AR manufacturers out there.

    Mil-spec in the civilian world is little more than a marketing gimmick. However, there are companies following a generally accepted set of standards, specifications, and practices and producing superior rifles compared to many of the best known brands.

    • Having worked to set up conformance standards for various bits of software and networking protocols in the computer industry, here’s one the reasons why vendors (or more accurately, their engineers) fall back on “MIL-STD:”

      Creating your own standards is expensive. Sure, it seems easy on the surface to just lay down a bunch of parameters and publish them.

      Then you get into the legal and technical issues in testing, verification, etc. Becoming a recognized standards organization is a huge chunk of bureaucracy and paperwork in and of itself, never mind the actual standards.

      Suddenly, all that talk becomes rather expensive.

      Just talk to any engineer who has served on an IEEE, AISI, ASTM or other standards-setting group. Ask them, after they’ve done one standard, if they’d like to do another.

      Most engineers would likely prefer to slit their own throats than do it again. I did it once, and you couldn’t find a team of meth-addicted draft horses big enough to drag me back for another round of that nonsense.

  13. I’d agree with the statement that “mil-spec is a good start”. If you’re new to the platform and don’t know what you’re getting into, you can’t go wrong buying BCM or Daniel Defense or any of the other “top-tier” manufacturers. Once you understand what all the lingo means, then you can feel free to diverge from the standards.

    Prior to owning my first AR, I was determined not to be one of those snobbed. I staked out a position that the center-point on the quality/cost spectrum was the best place to start, and I bought a Stag Arms. It ended up being a less than reliable choice, despite it being a well-respected brand.

    Ended up trading it for a BCM build, and I couldn’t be happier.

  14. My Sig Sauer M400 doesn’t have a high pressure tested barrel extension or bolt. They weren’t Magnafluxed either. When you think about it, there are thousands of other makes and models of firearms that never have any of this done. The only reason the tests are done is to make sure the bolts and barrel extension lugs don’t break off. Remember, they are made from cheap steels from the lowest bidder.

    Specifications just set performance baselines and confidence levels so that steps can be skipped and costs can be minimized over the long haul. The DOD doesn’t want $2000 safe queens. They want $600 pieces built with the materials and coatings they have at hand. The job has to get done, even if 50 of them fall apart and 20 were put together from the salvaged parts, with minimum expendature of resources. What that ends up meaning is that True MIL-STD M16s and M4 aren’t really that pretty and are not that accurate compared to what any of us could assemble. If you busted a piñata full of spec parts from differnt manufacturers around the country and could assemble a rifle, you have a very damn close to 100% chance that it will not quit on you, if taken care of.

  15. Aermet is 2.5 times stronger? I don’t think so. C158 probably still is the best material to make a bolt from.

  16. OK, I’ve built AR15s before. In fact, one of the ones I own I built in 1982, with a Sendra Corp/RIA, black, lower receiver. The buffer tube and buttstock I bought for it back then claimed to be MilSpec. The buffer tube has a straight back end-NOT slanted- and the buttstock itself is ALUMINUM covered in a textured rubber coat. I was in the process of updating it, and since I THOUGHT I had all MilSpec, I only bought a MilSpec buttstock as currently used on the M4. To my surprise and embarrassment, the new MilSpec buttstock is SLIGHTLY SMALLER than the buffer tube. So my question is this: Was I sold commercial in lieu of MilSpec back in 1982, or have the specifications for MilSpec changed over the years? Anyone know? Thanks in advance.

  17. Well done article. I have AR’s that aren’t Mil-spec that function flawlessly. Sure there are those that turn their noses up on a “Hobby gun” but I would trust it with no hesitation. I can’t understand how so many gun snobs base their opinions on silly criteria such as a staked castle nut. Sure internal details such as MPI testing and staked gas keys are important, but a castle nut is not that crucial. I say, learn as much about your gun as you can and maintain it and it will serve you well no matter what roll mark it has.

  18. the mil spec standard is more than just a starting point. metals used and dimensions are critical as testing has shown. when the government inspectors at colt’s or fn’s factory pull two rifles off the line and switch out parts, both must function 100% less the whole lot is rejected. trust me, neither colt nor fn want to go back and reinspect or rebuild 100 weapons because a gas block was off center. meeting mil spec standards has never been easy. think of the trials when every manufacture shows up with their test guns and one by one they drop out for one reason or another and in the end… colt and fn stand tall. low cost bidder? only if they can meet or exceed the grueling design tests parameters set forth by the military heads. it aint easy folks. and yes, the only ones who can claim DOD Mil-Spec are the actual manufactures of full auto military weapons i.e. Colt and FN on this day. ( Sabre Defense screwed the pooch) those weapons are built and assembled on entirely different lines than their semi counter parts. did you know that after each machine cut on any given barrel, each previous machined cut must then be gauged just to see if something has changed? that takes time… lots of time. i know of no commercial AR manufacturer who gauges theirs each step of the way.

  19. This article is good reading but, now im not sure who (ppl)/what (company) to believe, what i want is an AR15 or AR10 that a knowledgeable military person would use/buy if givin the choice to take into combat as far as an unfurniturized<~(made up word) civilian weapon.

    • The gun they take into combat is the mil spec Colt so if you are using that as your benchmark then you have the answer: Colt

      As far as there are better materials, yes there may be but until they are combat proven or tested in the field by the troops that will actually use them, then telling me that your material is better than current mil spec means nothing. Colt is a real world field tested weapon that troops entrust their lives to. Want to change the material, say, in the bolt receiver and convince me that it is a better material than Colts 158 Carpenter steel? Then have it successfully pass real world field tests and show me the protocals it passed and then we’ll talk. Until then, bull s h i t walks.

  20. Wallwallson, Milpec AR-15 barrels and bolts made of cheap steel that falls apart you say? Made of whatever materials they have on hand you say? Ha! Shows how much you know!

  21. Like it or not, “mil spec”, and “mil std” are the STANDARD. Anything less is just that-LESS. Without a standard, you get lower quality(“Hesse/ Blackthorne” ring any bells???!!!)

    Again milspec+ mil std doesn’t mean superior, but it means the besr “minimum” level of function. For an AR style rifle, WHY use 6061 grade aluminum( which quite a few civilian AR manufacturers use) when the better 7075 T6 aluminum is the “minimum standard?” If you KNOW ORD 4150 or CMV(akin to 41V45) barrel steel, chrome lined barrels are the minimum best standard, why use 4140 grade ,unlined barrels? 1:7 twist rates are “mil spec”, so why use 1:9?

    Colt, BCM,Daniels Defense, Knights Armament, LMT, even lowly Spikes Tactical and Palmetto State Arms all build civilian ARs to conform with “mil spec”, so why would someone buy a rifle from DPMS and Rock River, or Windham Arms rifles that often do NOT offer mil spec standard materials in their rifles BUT have
    The audacity to sell lesser quality for the same price as better manufacturers??

    If semi auto pnly, and 16″ barrels are the only things that keep the better manufacturers from being “truly milspec”, I’ll still stick to those who try to offer a rifle that meets those min. Qualities!

    Meets or exceeds mil spec means it can take a certain level of abuse and still perform.again, anything less is just that-less….

  22. Like it or not, “mil spec”, and “mil std” are the STANDARD. Anything less is just that-LESS. Without a standard, you get lower quality(“Hesse/ Blackthorne” ring any bells???!!!)

    Again milspec+ mil std doesn’t mean superior, but it means the besr “minimum” level of function. For an AR style rifle, WHY use 6061 grade aluminum( which quite a few civilian AR manufacturers use) when the better 7075 T6 aluminum is the “minimum standard?” If you KNOW ORD 4150 or CMV(akin to 41V45) barrel steel, chrome lined barrels are the minimum best standard, why use 4140 grade ,unlined barrels? 1:7 twist rates are “mil spec”, so why use 1:9?

    Colt, BCM,Daniels Defense, Knights Armament, LMT, even lowly Spikes Tactical and Palmetto State Arms all build civilian ARs to conform with “mil spec”, so why would someone buy a rifle from DPMS and Rock River, or Windham Arms rifles that often do NOT offer mil spec standard materials in their rifles BUT have
    The audacity to sell lesser quality for the same price as better manufacturers??

    If semi auto pnly, and 16″ barrels are the only things that keep the better manufacturers from being “truly milspec”, I’ll still stick to those who try to offer a rifle that meets those min. Qualities!

    Meets or exceeds mil spec mewans it can take a certain level of abuse and still perform.again, anything less is just that-less….

  23. I see a lot of names in this article but only one mention of Sig Arms , Im not a big fan of 556 or 223 would rather have 308 or 7.62 I have a piston driven Sig 716 the DMR and would match it to any other maker out there, The craftsmanship, Quality and reliability of this rifle is flawless. They make a 223 version and I cant say good or bad about it. But the rifle I have is one well put together rifle. I understand there is no mil spec or standard for 308 but If they come up with one Sig has really done a fine job on their rifle. Its the one Im betting my life on, I own others but this will be the one I grab

  24. I’ve thought a lot about mil-spec. Is it the best or just a starting point? Is their worse? Is there better? I’m still not sure one hundred percent but one thing keeps running through my mind, the Chauchat was mil-spec.

  25. There have been a few references to colt manufactured rifles as being civi and or defined as AR15 carbines/rifles. While that may be true and I don’t know all the details of what colt sells to Walmart I know that the new Colt A4 I bought says M16A2 on the owners manual so in no way is their any reference to this rifle being categorized in the AR-15 class of arms. As far as I can tell from research without having taken it apart yet the only thing different from a marines battle rifle and this 20 inch A4 is the select fire option which isn’t mil spec imo as this should be categorized as an option vs. a common functionality of all basic M16 or M4/variants such as a BCG spec ect ect.

  26. I’m trying to remember when “weapon made by lowest bidder” became “best.” For generations now military surplus has been correctly viewed as “bargain basement.” It will do in a pinch, but not on a regular basis. These days people talk about mil-surp bolt guns as though they are sacrosanct – they’re not. They aren’t a piece of history. They aren’t an example of premium craftsmanship of their era. They are an example of something mass produced to be beat up and neglected by barely trained saps who are about to be marched off into a meat grinder. Sporteriszing is often the best thing to happen to those guns.

    You couldn’t pay me to take a milsurp M16Awhatever/M4. For that matter, if some day congress manages to get M14s transferred to CMP after having the auto lug ground off I still won’t buy one because there is absolutely no way to tell how many M60 proof loads(70,000 PSI) have accidentally been shot through it over it’s life span. If I just have to have a forged receiver I’ll buy an LRB.

  27. My career is centered on specs.
    As you point out mil spec. Iike any spec insured across the board compatibility.
    But like codes it typically establishes a minimum standard. What this means is that no product or manufacturer will provide anything other than what the spec calls for.
    There is a whole world of products which exceed mil spec requirements. And if superior performance is what your interested in you have no choice but to venture away from mil spec.
    As far as I am concerned there is only one reason to go mil spec and that is to create a platform that comes in all respects to military grade.
    Doesn’t interest me at all and I’m glad you addressed this subject.

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