Anderson AR-15 lowers no longer mil-spec?

It appears that Anderson has made the decision to change the thread depth on their AR-15 lower receivers so that they will not accept the standard 1″ grip screw found in every mil-spec AR-15 lower in America. In the photo below you can see that the grip screw hole is not threaded the whole way through.

Photo credit: user MaverickAA

Photo credit: user MaverickAA

My friend Scott from The Gunshow Podcast (a great podcast if you haven’t checked it out) let me know that Anderson claims that the 1″ grip screw was creating malfunctions by interfering with the fire control group. I have also have seen rumors on ar15. com that there was a manufacturing error that left the threads unfinished.

Some AR-15 builders have decided to take the matter into their own hands with a 1/4-28 tap, threading the hole the whole way through. This is a sure fire way to fix the issue if you feel up to the task.

Photo credit: user kwrangln

Photo credit: user kwrangln

Anderson sells a 3/4″ long grip screw that will not run out of threads before being fully seated. They have it priced at 99 cents, but was a bit shocked when I saw the shipping price of $11.22 for ground shipping on just the grip screw. Did I put the zip code if for the moon?


Alternatively builders can just run down to their local hardware store and buy a 1/4-28 screw that is 3/4″ long to get around the threading issue.  Do you think that the fact that you can no longer install common grip screws changes Anderson Manufacturing lowers status as “mil-spec”?

Patrick R

Patrick is a Senior Writer for The Firearm Blog and TFBTV Host. He likes guns and has liked shooting guns for as long as he can remember. You can follow Patrick on Instagram @tfbpatrick, Facebook, or contact him by email at

The above post is my opinion and does not reflect the views of any company or organization.


  • flyingburgers

    That’s the problem? I thought the article was going to say that they went Metric or something…

    • Grindstone50k

      Apparently it’s the end of the world for inexpensive AR lowers.

  • El Duderino

    So either get a $10 tap or a $12 screw? Dumb.

    • Ken

      I’d stack a few more washers under the screw head, put a section of metal tubing between the screw head and locking washer, or cut the screw down.

      • Just say’n

        You might be a redneck if….

      • Bob

        I think I could probably get it to work with some duct tape.

    • ostiariusalpha

      Or, like Patrick mentioned, you can go to the hardware store and get the exact same screw for 12¢. Hell, you can use it as an excuse to get out of the house.

  • Joshua

    that depends, does the Military Specification specifically say that the grip screw must be 1″ or was that a decision on the part of the supplier? if the former than they no longer qualify as “Mil-Spec” if the later, then it depends on if the military would alter the specification to exempt them as a result of changed parts interchangeability.

    • Jordan Bowles

      The mil-spec screw is a 1/4″-28 x 1.125″ fillister head machine screw. Not the 1″ Socket head cap screw shown above. With a standard A2 pistol grip a 1.125″ screw with a lock washer should never cause any issue with the trigger or otherwise. However, if you use the standard screw with a pistol grip like Magpul MOE or MIAD you may run into trouble as they are designed to use a screw specific to those grips that happens to be a bit shorter. This is just a case of people getting what they pay for, Anderson lowers are great for what they are… the cheapest lower worth even considering.

      • Thomas Gomez

        You are %100 spot on. The gentleman who taught the Armorer course I attended said that when his unit went into Panama his A2 grip was loose. He and his “battle buddy” broke into an Esso gas station, found a flat head screw driver and re-tightened the grip screw. You can find a flat head screw driver pretty much anywhere in the world. When I see a fillister machine screw on an Ar-15 I know the company who built actually gives a damn or the armorer who built it knew what he or she was doing.

        • Just say’n

          Great point. The LPK I bought for my Grendel (I forget the brand, maybe CMMG?) came with a slotted fillister head (flat-blade screw driver slot). So they are out there.

        • Chase Buchanan

          I didn’t know there was another name for flathead or slotted screws. “Fillister”…I kinda like the way that sounds.

          • Thomas Gomez

            …It does sound neat!

          • PeterK

            Slotted is the shape of the tool head used to engage the screw. Filister is the shape of the screw head itself. That kind of rounded cylinder shape.

        • flyingburgers

          The problem with the slotted head is that there’s the potential that the screwdriver slips out, damaging something or hurting yourself. So people have a tendency to undertighten it. The SHCS is impossible to mess up. If you look at Ikea furniture, designed for amateurs, they always use socket head (except the quarter turn fasteners, where they don’t want torque).

          • Thomas Gomez

            Hurt yourself tightening a grip screw…? I think your okay if you use a large screw driver. Amateurs keep armourers busy. Your mileage may vary.

          • flyingburgers

            Difference between the AR and the AK… The AR requires a trained precision armorer because amateurs will cause it to fall apart. The AK… riveted together.

  • Squirreltakular

    I recently tried to populate a new Anderson lower for a build and ran into the same problem. Not only that, but the space that the magazine catch sits in on the left side is tight and grabs at the catch when you press it. The front receiver takedown pin was very tight as well. These will obviously wear in, but they shouldn’t have to. I didn’t bother trying to install any other parts.

    Screw these guys. I’ll keep it to sell during the next scare, but they’ve lost any hope of future business from me.

    • Cymond

      I have a Delaware Machine lower that’s so tight, I had to sand the takedown/pivot pins to get them in. The internal rear pocket (by the takedown pin) was so tight that an upper couldn’t fully close, and nearly got stuck when I pushed it down. I had to Dremel that area out to make the lower useable.

      I bought the lower years ago without doing any research, before I knew anything about AR-15s. It turns out that Delaware is not normally a gun company, and I overpaid by about $40. No regrets though, because it’s the only lower I have that’s eligible to be built as a pistol (I think). I’m unclear about the lowers I bought while I was still in CA.

      • Patrick R.


  • Jared Vynn

    I haven’t found a 1/4-28 at any of the hardware stores i have frequented and i have been actively looking.

    • RocketScientist

      Are you in America? If not thats probably understandable, but any hardware store stateside should definitely have a decent selection of 1/4″-28 x Whatever-length-you-need screws. Can’t imagine one, much less multiple hardware stores not having any in stock.

      • Jared Vynn

        In both Florida and Tennessee I haven’t been able to find one. Many had the spot for them, but none in stock.

        • RocketScientist

          Wow, thats really crazy. Not only is it not an oddball size, its one of (the?) most common machine screw sizes used out there. That stinks man. If you’re near a moderately sized town/city, most will usually have an “industrial supply” or “bolt and screw supply” type of place. Like a hardware store, but more geared towards commercial customers (though most will usually sell to regular joes). Might be worth checking them out. I’m in the Tampa-bay region, and I know of at least 4 stores within a 10 minute drive that will have these in stock. If you’re anywhere near here let me know and I’ll pass along some suggestions. Sorry bout your luck!

          • jonspencer

            Here is a partial list of stores that carry those machine screws as in store stock,
            Home Depot, Lowes, Ace, True Value, Menards, Do It, Advance Auto, NAPA, Orileys, Fastenal, etc etc..

        • patrickiv

          Most places have free ship-to-store so you can order it online and pick it up in a few days.

        • Grindstone50k

          Not even big box stores like Lowe’s or Home Depot?

    • Rodger Young

      1/4-20 is National Coarse and 1/4-28 is National Fine, pretty much the standard pitches available in 1/4″.

  • Paul Epstein

    Must have gotten mine at just the right time, still has the full 1″.

    • junyo

      Same here.

    • Grindstone50k

      Got two, no problems. LGS that supplies them never had an issue either.

  • no

    They should take the stupid horse rollmark off while they’re at it.

    • Gene

      The rollmark doesn’t bother me, but I own horses. I’m more interested in the price and fitment.

    • Grindstone50k

      Yeah, that’s my biggest complaint with Colt receivers too.

  • Nay Sayer

    Oh, please ! Those are called “manufacturing errors” – and Anderson Manufacturing, instead of destroying them or selling them as what they are (out of spec lowers), they’re pretending “working as planned”. I think it was about two/three weeks ago on another site – some company was selling out of spec lowers, that required of a special bolt catch (5.56 lower that needed of a 9mm bolt catch, or something like that). They made it CLEAR those were “factory seconds” and you would need a special part – which they included with the lower.
    I always thought Anderson sucked – no surprises here.

    • John

      I had a $100 billet lower from Botach that the hammer would fall only half way. Half way. So a 9mm bolt hold sounds pretty good.

      • Bill

        “Botach” – We’ll there’s your problem.

  • Caffeinated

    Since none of these lowers are machined internally to M-16 dimensions and lack the third pin hole; I would argue that no semi auto lower is truly “mil-spec.” Some like BCI and GPI are internally machined to M-16 dimensions but again lack the deadly third pin hole.

    • Patrick R.

      Pedantic much?

      • RocketScientist

        I’d say questioning whether omission of an entire hole which functionally changes the firearm counts as enough of a deviation from standard to no longer deserve the name “mil-spec” is pretty much EXACTLY as pedantic as questioning whether changing the depth of threaded engagement in another hole counts as enough of a deviation from standard to no longer deserve the name “mil-spec”.

        • Patrick R.

          Mil-Spec has become a term that qualifies a lower or AR-15 part as meeting the industry standardized pattern, at least that is how I see it.

          By “non mil-spec” I meant that it will no long accept everyone else’s “mil-spec” parts.

          • Rodger Young

            The pistol grip screw used on M16 and M16A1 pistol grips is shorter than that used with the A2 grip.

    • Daniel


    • Spencer W

      My first thought..

  • Phil Hsueh

    The reason for the $11 shipping has to be because the CEO is the one who’s personally handling the shipping of these screws and the $11 covers the cost of his time. That’s the only reason that I can think of why they’d charge so much for something that could be just dropped in an envelope and sent via st class mail.

    • HSR47

      Actually, it probably has to do with the way their website calculate shipping charges.

      While they could probably get away with just dropping it in an envelope and sending it first-class mail (49 cents postage, plus materials and handling), the backend software for their website doesn’t know that.

      • CountryBoy

        Unfortunately, the USPS doesn’t always play well with “dropping it in an envelope and sending it first-class mail”, as it falls under the “rigid item enclosed” rules, requiring extra postage and hand-cancellation (i.e. “non-machineable”). It will as often as not get lost in the ether.

        Sending it as a normal package costs more, at least $2.25 or so if done online, plus the time to pack it and the materials involved, the logistics in communicating all this so you can check your order status later as well.

        Besides, if it doesn’t have tracking, you’d be surprised at how many of those “never got there”, whether due to the USPS or the intended recipient claiming non-receipt.

        I would invite those who think it’s a matter of a $0.49 stamp and a business envelope to try it.

        Not to defend Anderson, but it costs just as much to package a single grip screw as it does an entire grip or LPK, for the most part. The weight will differ, increasing the postage, but the rest of it remains the same. Anderson probably knows their overhead for all this and this keeps folks from buying little pieces one at a time – or gets folks to visit their local hardware store.

        • HSR47

          “I would invite those who think it’s a matter of a $0.49 stamp and a business envelope to try it.”

          I never said it was a simple matter of just doing that; I said that they might be able to get away with it. Given the weight limits of first class mail, an envelope with a single grip screw and a minimal paper invoice should make weight.

          That’s not to say that it’s the only issue.

          You are completely right about the USPS being apt to “lose” packages, and you are completely right about employee time required to properly package things for shipping.

          Ultimately, mediamail is probably the answer, and given weight (under one pound) and the high-volume commercial shipper, that should be significantly cheaper than most box-based shipping options,

          • CountryBoy

            Media Mail is just that – for media only, like CDs and (IIRC) books. Sending general merchandise through Media Mail is likely to get the recipient a “postage due” notice, and it isn’t always cheaper to begin with.

            We send small items out all the time, and the best way we’ve found is trackable First Class parcel (not “Parcel Post”) for that $2.25 or so, plus materials and time.

            If you want to see what others charge, buy a few small items from Numrich (Gun Parts Co.) and you’ll see that no one else really charges under that $2.25 for shipping, and most charge more because their overhead is higher.

            But if you want it trackable, 1st Class is the least expensive.

  • Sianmink

    Serious question.
    Instead of extending the threads or paying $12 for a grip screw or going to the hardware store, why not just use a cutoff wheel and make your existing grip screw a little shorter?

    Of course best case, Anderson makes them right in the first place, but that’s clearly off the table.

    • HSR47

      Because to do that correctly, you’ll need a nut.

      The proper way to cut a bolt or threaded rod is to first thread a nut past where you intend to cut, make your cut, clean up the end of the thread a bit so it isn’t unduly sharp, and then thread the nut back off to bend the end back into the proper place.

      In this case, unless you already have a properly-threaded nut to use, you’d have to go out and buy one. At that point, it would be cheaper and easier to just buy a shorter screw.

      • Sianmink

        If I do it without a nut and it works, did I still do it wrong?

        • Dan

          Yes and you will possibly tear open a rift in the time/space continuum. Unless you divide by zero first. Then you will be ok.

          • RICH

            LMAO ! ! ! Thanks, Dan, I needed that this morning ! !

      • patrickiv

        Cut it with a hack saw and use a triangular file to clean the threads. It’s not that hard.

      • displacer

        I just always clean the new end threads up a bit with a needle file or give it a quick spin on a bench grinder to put a tiny bevel on the top, hasn’t exploded and killed me yet

      • Rooftop Voter

        In instances where you have enough depth on a machine screw, I would first run a threading die onto the threads. After you have ground it down or hack sawed it to the desired length, unscrew the die and the threads should clean up OK. Putting a chamfer on the new end also helps and then I wire wheel it to soften the sharp edges. I have done that for eons.
        If the screw is too short for the above, I use a Snap On thread chasing bar (the tool that has 8 different thread pitches on it) and work the new threads until a nut will run smoothly on it.
        There, that was easy and I didn’t even stay at a Holiday Inn Express last night.

        • HSR47

          You’re right; A nut really isn’t the “right” way to do it. It’s just the inexpensive field expedient.

          Thread on a nut, cut/grind the bolt to the desired length, use a file (or a field expedient) to chamfer the end, then thread the nut off to clean up the threads.

          Sure, you CAN opt to use all the tools you mention, but a nut is cheaper, and it works too. When you have to do it frequently, it makes sense to have the tools to do it right; On the other hand, when you only do it once in blue moon, it often makes more sense to opt for the inexpensive method that works almost as well.

  • Tom Steffner

    Patrick R, if you having a problem with one of our lowers, please contact customer service at 859-689-4085 ext 106 or email Tyler at We stand by all our products 100%

    • Grindstone50k

      Can you confirm if this is a manufacturing defect or a design change? Seems to be a bit of misinformation out there and an official response would help sort things out.

      For what it’s worth, I am a satisfied Anderson AR lower customer.

    • cawpin

      Are you going to tell us if this was a design change or not?

      • Geared AndReady

        cawpin if you read the response Tom posted below he said “The spec has not changed” and them posted a blueprint. So that seems pretty clear that nothing has changed.

        • cawpin

          I could not find another response from him, too many comments. Thanks for the info.

  • Cymond

    I always thought it was odd that Anderson blems are $42 online. Now i know why.

    Personally, I don’t think this is OK. I don’t mind if something isn’t “milspec” but it needs to at least work with standard parts.

  • patrickiv

    Just cut off the end of the screw.

  • BillC

    Damn, literally just bought one from my LGS today. They should have it in Tomorrow or Minday.

    • Grindstone50k

      Apparently it is literally trash now.

  • Wolfgar

    I did three builds using Anderson uppers and lowers.They were very tight and problem free. I have read where others have had problems with Anderson receivers but i cannot say I have had any thing but 100% satisfaction with them. I don’t care for their thread depth change for the pistol grip but it is a minor inconvenience. They are top quality receivers for a great price. They shoot every bit as accurate as my expensive billet receivers. Anderson is a great value.

  • Grindstone50k

    I have two Anderson lowers. Zero problems installing Magpul grips with factory-provided screws. Bought the lowers retail less than a year ago.

  • Barney Samson

    The unthreaded portion is a non issue unless it was needed to adjust the trigger by the way we all know about. Non issue that is, unless you don’t happen to have the shorter fastener on hand and have no way of shortening the longer one. Anyway, a flat washer or two would take care of it bottoming out.

  • tirod

    Anderson isn’t the only one. Read arfcom over the years and other makers have done the exact same thing. It’s been discussed in the past – and I will bet a dollar to a donut that in the next month some AR builder will point out their high dollar lower isn’t completely threaded.
    Be advised, grip makers aren’t supplying the GI screw because of it.

  • Tom Currie

    In the AR community “mil-spec” is nothing but an advertising term with no firm definition.

    Someone probably does make a fully mil spec lower, but I’d be hard pressed to figure out who might be making one for sale outside a government contract. Remember, there is no military specification for an AR15 — there are military specifications for the M16, M16A1, M16A2, M16A3, M16A4, M4, and M4A1 – and each of those sets of specifications covers EVERYTHING about the weapon, not just dimensions, but materials, surface treatment, finish, and markings. If the lower isn’t made of exactly the right metal, finished in exactly the right treatment and color, and marked exactly as the military requirements specify, then it ISN’T really “mil spec.”

    Even if you choose to disregard materials, finish, and markings and say that for our purposes “mil spec” just means that the lower is made to the proper dimensions, then you still won’t find many (if any) “mil spec” lowers — otherwise you could take that lower and install a complete set of military parts to create your own select fire M16 or M4 — last time I looked, that wasn’t what was on the civilian market.

  • jerry young

    not a big deal, use a shorter screw found at any hardware store or re tap it whats the problem? if you can build a gun but find this as a problem then there’s no hope for you ever getting your AR to work, it’s only a bolt! I have 2 Anderson lowers and not a problem with either

  • Dual sport

    You have never ran into this before? It’s somewhat common on other lowers as well. It’s not a big deal.

    Far too many people expect perfect and mass production to be used in the same sentence.

  • Agitator

    After several difficult builds with Aero receivers, I’m hesitant to believe that they’re built to any specifications at all.

  • Mystick

    $12 for shipping?!!?!? On something weighing in the single-digit grams?!?! That’s some Grade-A Premium BS right there.

    • Cymond

      Sloppy website design. It doesn’t calculate based on size or weight.

  • SD

    Anderson is the furthest thing from “milspec”.

  • lbrty2112

    Anderson’s shipping cost is ridiculous. I wait for their lowers to go on sale on Aim Surplus. Cheaper sales price and half the shipping cost.

  • smartacus

    99 cents + $11.22 is too cheap for me. Make it Fedex Same Day.
    Heck, make it Same Day International.

    And i don’t like HEX bolt, make it PENTALOBE or SECURITY TORX to force me into spending more money on yet another tool set. (oops i just remembered i already got a set)

  • Tom Steffner

    Per the mil-Spec a depth of .625 Min,

  • Tom Steffner

    This design has never changed

  • Bob

    I have a 2 year old M&P 15T and the grip screw hole threads did not go completely through to the inside of the receiver. I use a 1/4 inch long set screw, above the grip screw, to limit trigger travel after reset. This greatly reduces trigger creep/take-up. After installing and adjusting the set screw (along with thread locker), I then use a 3/4 inch long screw to hold the grip on. The threads looked more like a manufacturing problem of the tap not going completely through, than a design change by S&W. Easy fix was to run a tap completely through and the issue was fixed. By the way 1/4 inch by 3/4 or 1 inch long socket head cap screws run around $1 each in my area, not $.10.

  • Duane

    I found this out with my last build using an Anderson lower. I contacted Anderson and they told me that the grip screw threads don’t go all the way up. I purchased a shorter stainless steel bolt from Lowe’s and using a skinny socket got the grip on tightly. I have since changed it out with a hex head bolt.

  • Geared AndReady

    the Article Patrick states that a friend of his named Scott told him
    that Anderson sells 3/4 grip screws because 1″ screws may interfere with
    the fire control group. However “Scott” does not say Anderson has
    stopped threading the screw holes all the way through on the lowers. Scott says Anderson sells shorter grip screws, and never mentions the lower.

    Also we do not know the source of Patricks lower, this is important, if he purchased it directly from Anderson or from a dealer. Anderson routinely sells Blemished lowers at discounted prices to their dealers. Patrick could have purchased one of these blem lowers unknowingly from a dealer and the blemish was the depth of the grip screw hole.

    Lastly the only proof we have that this may indeed be a problem are 2 pictures one with a tap in it illustrating the defect. None of the pictures show this to be an Anderson lower or demonstrate the problem.

    Lastly several posts down Tom Steffner from Anderson clearly states that they have not made any changes. Posted the Mil-Spec showing a minimum depth of .625 inches which is shallower than the .75 inches claimed in the article, which would still put the lower “in spec”.

    I would say that most who may be having issues with a lower from Anderson may have purchased the lower from a retailer/dealer who could have bought Blemished lowers at a discount from Anderson and sold them to you without telling you. Anderson’s page clearly states Blemished when purchasing a lower.

  • Geared AndReady

    Okay just measured the grip screw thread depth on Anderson lowers. It is .75
    inches. Now before you tie up a noose I measured something else. I put a
    grip screw in a Mil-Spec pistol grip with the correct washer and measured how far the screw protruded through the grip. It was 3/8 of an inch. So the grip took up over 1/4 of an inch of thread space. What this means is if you use a Mil-Spec grip and a
    1 inch screw with the correct washer it will work just fine without bottoming out the threads.

    So whether the grip screw is 1/2 inch or 3/4 inch or 1 inch, if the thread hole depth is 3/4 of an inch all screws will work. As to whether or not an Anderson lower is Mil-Spec or not due to the screw hole being 3/4 of an inch deep is irrelevant.

    Mil-Spec doesn’t really matter in this case. And the 1 inch screw will work if properly installed with a Grip washer in a Mil-Spec Grip. It looks like Patrick just tried to screw in a 1 inch screw without a grip on it,

  • Secundius

    Is this a Possible Reason, why Colt/Colt’s hasn’t Won a Military Competition Shoot-Off since 2007, using “Inferior” Parts…

  • Barney Samson

    Mountain out of a mole hill imo. Use a thick (or multiple) washers. Or cut the fastener to make shorter. No nut or die is absolutely needed to thread onto a bolt before cutting it off shorter, although it’s a good practice. That is, unless you’re using a chainsaw to cut the bolt off. You WILL want to dress the cut end w/a dremel or fine file though. Unless the hole needs threads all the way through the hole (like to adjust the trigger by the method everyone’s aware of), just leave it as-is. Cutting the threads w/a tap risks damaging the existing anodization, as well as will create a non anodized area in the lower.
    FWIW, some if not all DTI lowers also do not have threading all the way through- but a 1″ length-under-head fastener works just fine, so I’m wondering if a 1″ fastener was even tried or if the assumption was made it would not fit w/o actually trying it…

  • Barney Samson

    The unthreaded portion is a non issue unless it was needed to adjust the trigger by the getto method we all know about. Non issue that is, unless you don’t happen to have a shorter fastener on hand and have no way of shortening the too-long one. Anyway, an AN flat washer or two would take care of it bottoming out. Those who insist that every detail be mil-spec will be put off, no doubt.
    Had a DTI on my bench that was made the exact same way. Took all of 2 minutes
    w/a tap to finish the threads. Don’t like the idea of damaging the anodization
    though, not to mention tapping leaves the newly threaded area bare.