How to make a Polymer AR-15 Lower at Home

Sebastian and a friend have described in detail their latest successful attempt at making an AR-15 lower at home. They used a CNC mill to machine the lower out of a block of Delrin.

Neither of the pair were machinists. Anyone with enough motivation can learn how to make an AR-15 at home. If you can’t afford a CNC mill, you could always build one yourself.

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Máté

    Looks great. Is this legal?

    • Jingles

      Legal if for personal use, not sale.

      • Máté

        Thank you!

      • Other Steve

        Jingles is correct, not for FFL sale. It doesn’t even need any markings like a serial number.

        HOWEVER it does still have meet NFA, GCA, and 922r regulations. So no making a SBR without registering it first. In this case it would be a Form1 SBR receiver.

        I did the same for my MP5.

      • Shooter

        Not entirely correct. It’s legal to manufacture a firearm for your own personal use, provided that it complies with the NFA and local state laws. You are not required to add a serial number if you choose not to. You CAN sell it to another resident of your state (or another state, provided it goes through an FFL in the purchaser’s state) who can legally possess the firearm. What you cannot do is make a business out of making firearms without a manufacturer’s FFL. Who defines whether you’re in business? The ATF. How do they define it? However they feel like it – if they think you’ve crossed the line and have evidence to that effect. From a realistic point of view, you can probably make plenty of rifles for yourself, and if at some point down the road you decide to give one away or sell one to a friend, probably kosher…if you put up a table at the local gunshow and start selling off a stack of stripped homebrew Delrin lowers, you’d better keep the KY handy.

    • jdun1911

      There are no federal laws in the USA prohibiting the manufacture of firearms for personal uses as long as all the NFA rules applies. In fact you do not need to place serial numbers on the receivers for firearms you made yourself.

      If it an NFA item like suppressors/SBR/SBS, you need to fill out the forum and paid the $200 tax stamp. Wait 3 to 7 months to get it approve. Then it become legal to produce that one item. The serial number will be the same as the one you filled on the NFA forum.

      If you can afford a hobby CNC machine you can almost built any firearms receivers and some parts. AR15 parts are pretty common. They should have order 0% forge receivers. I got some from DS Arms few years back for $20 or so IIRC. Not sure they sell them anymore tho.

      • Other Steve

        I built up my MP5 from a receiver. Even CNC’ed out some jig parts to make it go a little easier.

        I would have saved so much time and money by just buying one!!! I’ll never do that again.

        The idea behind this though is that in the not-so-distant future, smart-mills and laser sintered aluminum/titanium will be affordable to the point where it won’t be unreasonable to “print” most firearm parts at home.

      • jdun1911

        In most cases it is better to buy than make one. My 0% receivers are still 0% receivers today because buying already built AR15 receivers are 3 to 5 time cheaper than if I make it myself. My 0% are now use as paper weights.

        Building suppressors are worth it and so are SR25/AR10 receivers. The problem with NFA you have to wait a long time before it gets approved.

        It takes about 5 to 10 hours to built your own suppressor. Pretty easy IMO if you know how to weld. Depending on the material cost it could run as little as $30 or over $100. You are basically looking at around $300 ($200 tax stamp).

      • Other Steve

        I disagree on suppressors. TOTALLY makes sense to buy!!!

        If you think as a hobbiest, you can build a suppressor with ANY of the following features for less than it costs to buy one you’re crazy.

        Quick Attach hardware
        Any Inconel at all really
        Heat treated 17-4PH and other exotic steels
        Type III hardcoat anodizing
        Thick grade5/9/23 titanium tube
        Robotic welded parts
        Pressed baffles/tube assembly
        EDM’ed tapered bore

        Now, take products that have 5 or 6 of those out of 8 and you have things that are absolutely impossible to make one off cheaper than you can buy.

        That said, you can build a silencer that’s 85% as good as a top of the line one, but you’re on your own for time, ancillary costs, and if anything happens there is no warranty. For all that headache, I’d rather just pay a little more.

      • Máté

        Thanks for the answer.

    • Bryan S.

      Legal for personal use, and you could sell it, if you are not in the business of manufacturing firearms (Ie, made it, didnt like it, or wanted to trade it for something), and then all you would do is have to properly serial the receiver according to ATF guidelines.

  • Philip Luty would love to see this one…
    Now for more anti-gun, anti-3D at home. Luddite Media nonsense!

    • Phil passed on last year on April 8th. Cancer finally got the best of him.

      • noob

        sorry to hear about mr luty. he was a brave man.

  • Nicholas Chen

    An easier way would be to create it in 3D and print it out.

    • Other Steve

      Yea, it would be “easier” but most consumer available printers (makerbot etc) do not have the resolution or polymers with the proper strength…. YET.

  • 276 pedersen

    “So I’m trying to make a delrin lower first for use with a .22 cal upper, and if that works I’ll order some aluminum and make another lower for use with a .223 upper.”

    So just keep in mind this is for a .22LR

    • Other Steve

      223 would work for awhile, until it wobbles it’s own holes out. I think the point here is proof of concept.

      The idea of banning firearms becomes a little nonsensical if they can be readily made at home by non-professionals.

    • Geodkyt

      Steel bushing inserts for the pins would pretty much eliminate the wobble issue, at least for a casual shooter. Now, if you burn tens of thousands of centerfire rounds through it, it’s going to end up “unservicable”. Of course, despite the fact that they generally do last much longer, I believe the “service life” of the receiver (as listed in the milspec) is less than 25,000 rounds, and you’ll already have probably swapped out the fire control group, bolt carrier & bolt, and be looking for a replacement barrel by then, I don’t think it is a serious issue.

      Likewise, even Wolf is going to cost you $200/1000 rounds, and M193 or M855 will cost you between 1.5 & 2 times that. (Yes, you can find M193 around $300/1000… if you look hard.) If you can afford enough ammo to wear it out, you can afford to replace it.

  • Andy

    What if you took these plans to a CNC shop? Could they legally make them? Would it be worth the cost vs purchasing new?

    Also is this something you could just send in to shapeways and wait for it back in the mail ?

    • noob

      Shapeways would be able to make it, but they won’t because they have a strict no-illegal-items, no-weapons, no-weapon-parts policy.

      They inspect every file you send them for buildability and have called the authorities before over things like credit card skimmer enclosures.

      I don’t think they’d raise a ruckus over trying to build an ar, but I’m pretty sure they’d just delete the file and refuse to take your money.

    • They couldn’t legally make it for you. But if you have the equipment it’s legal for you to make your own that you can never sell or transfer.

      Also check out the 80 percent crazy … this site sells tools for completing AR lowers that were 80 percent completed. you buy the 80% lower and then finish it your self.

      • Bryan S.

        You CAN sell a rifle you have built… you just cant make a habit 9buisness) out of it without proper licensing.

    • Geodkyt

      If someone else builds it for you, it is legally defined as “manufacturing”, which requires them you have a manufacturing license appropriate for that class of gun (including the right type of SOT for NFA stuff)

      If you do it for yourself, it is “making”, which is perfectly legal provided it is a gun that is legal for you to possess. (Which is why, if you’re making something that falls under NFA, you have to have your approved Form 1 in hand BEFORE you start making it – REGISTERED NFA is ok, unregistered NFA is a felony.)

      “Make” is something you do with the intent that it is for your personal use. It does not require an FFL.

      “Manufacturing” is something you do with the

      • Geodkyt

        “Manufacturing” is something you do with the intent of transferring it to someone else, and it requires the appropriate licenses.

        You CAN transfer something “made” for personal use- just like you can later transfer a gun you bought for personal use. If your transfer would have been considered a “strawman” purchase or “dealing without an FFL” if it involved a factory built, storebought gun, then the same transfer involving a homebuilt “made” gun would also be illegal. Also, you don’t have to put a single marking on a homebuilt gun, EXCEPT if it is NFA regulated OR you are about to transfer it – ATF insists that in either of those cases, you MUST mark the gun, and the same standards on marking apply.

  • John Doe

    Something I can defend myself with when they try to take my 3D printer! My right to print will remain!

  • Lance

    That will make the ATF crap there pants. LOL

  • fred

    Umm cool..
    But.. are we sure the Gov. won’t freak about this?
    This is manufacturing..
    and.. are we sure you can’t run around with an arm with no serial?

    Just asking..

    • noob

      Legal for personal use in the USA, but you can never transfer a non-serialised weapon to another person. Also you can’t SBR without proper forms and $200 tax stamp.

      outside the usa… yes governments will totally freak out.

      See the other post about india and it’s black market. Cheap homemade guns of usable quality being made by unskilled computer users means a huge bite out of their govt owned gun business, so that makes an economic incentive for countries like that to ban this technology. That’s before even considering their attitude to the politics of personal freedom or the threat to their regime.

      • jdun1911

        The two main reason why people make their own firearms in the USA are:
        1. Educational.
        2. Customize

        You save a lot of money, time, and stress by buying it from the internet or gunshop then making it.

        You can’t ban this type of technology. You can built your own CNC machine using parts from hardware store and download the free software from the internet.

        You don’t even need CNC machines to make firearms. You can do the old fashion way by using a mill.

      • Geodkyt

        Actually, you CAN transfer a homemade gun legally in the United States. The ATF even has issued letters giving guidance on the requirements.

        There is a LOT of misinformation out there concerning “homebuilds”, but basically, the same rules apply as if you bought the gun in a store — you may not build it with the “intent” of transferring it (think “strawman build” instead of “strawman purchase” — just remember that building for your own personal use is “making”, which is perfectly legal; but building with the intent to transfer is “manufacturing”, which requires a specific FFL), and you cannot build something that is illegal for you to have (unregistered NFA, 922(r) violations, if you’re a “prohibited person”, etc.). AFTER you have a homebuilt that is legal, you can dispose of it the same way as if you bought it through an FFL dealer.

        The thing is, you CANNOT transfer a gun you have made that lacks the legally required markings (there ARE older guns out there that pre-date the marking requirements, and are thus exempt). Nor can a later party “make it right” by marking a gun that has already been transferred (with carefully specified exceptions, for instance, a legal importer is REQUIRED to add certain markings if they are lacking, and is required to serialize or re-serialize a gun to ensure it has a “unique” * serial number.) So the “maker” “manufacturer”, or “importer” has to ensure all the required markings are present BEFORE it is “transferred”.

        In short, the “maker” (you) MUST apply the appropriate markings BEFORE the gun is transferred, and the marking requirements are the same as they would be for a Form 1 NFA registration — maker’s name, city/county & state where made, model name (if the maker has assigned a name – you don’t have to), and a “unique” * serial number. (No, this DOESN’T mean that every homebuilt requires a Form 1, NOR does it mean that ONLY NFA guns made on a Form 1 are allowed. ATF has just said the legally required markings are the same for a homebuilt, GCA-only regulated Title I gun as they would be for a homebuilt, NFA-registered Title II gun.)

        You can only use the standard English version of the “Roman” alphabet and “Arabic” numerals for the required markings, there are depth requirements for all markings, and a height requirement for serial numbers. All serial numbers must include at least one digit, and no special characters. (ATF has had issues when they entered info into computers, having agents trying to transcribe Cyrillic characters, REAL Arabic numerals, accented characters, etc.)

        * “Unique” meaning that that particular “maker” (homebuilt) “manufacturer” (FFL licensed manufacturer), or “importer” (whether an FFL importer, or an FFL licensee with a one-shot import license) has not previously used it on a gun they have “made”, “manufactured”, or imported — it’s perfectly fine if you, your Uncle Bob, Century, Colt, and HK have all stamped “10000” on a gun; each of you are different “makers”, “importers”, or “manufacturers”.

  • Ian

    Quite possibly the greatest example of what you can do, but shouldn’t.

    • David/Sharpie

      Why not? He’s building this for a .22, not a full calibre, but even so, people have .50 BMG conversions that use reg lowers, I’m sure this would be safe for a .223/5.56 upper, I wouldn’t wanna shoot it with my hand the first try, but I would with a string

    • Geodkyt

      The lower receiver just needs to be strong enough to take the wear of the trigger group pins, and the rather minimal force of the buffer spring (transmitted to the buffer ube threads in the receiver.)

      The BARREL COLLAR (an integral part of the barrel assembly) takes the real force.

  • noob

    My big question is: what happens if a scared government clamps down on the sale and posession of gunpowder?

    I certainly wouldn’t want to make cordite at home. In places like Australia, you need to show your gun licence (which is hard to get and harder to keep – you have to compete in sport shooting twice a year to keep your “leagal excuse to posess”) in order to buy powder and the other sources of powder like starter pistol caps are tightly controlled.

    • Fritz

      If you’re really worried, it is fairly simple to manufacture black powder even with no chemistry experience. I am sure there are free cordite and nitro-cellulose manufacture guides online. There are at least two large (40gb and 75gb) torrents containing information relating to manufacture of ammunition and firearms, as well as survival skills, manuals, and miscellaneous information. One is known as The Dokument and is either 40gb or 10gb (10gb version omits most of the video). There is also the Mega Folder containing everything The Dokument contains plus a plethora of information on physics, chemistry, history, medicine, electronics, mechanics, robotics, computer science, mathematics, and additional survival information.

      Unfortunately, nobody seeds the 10gb Dokument file anymore and no trackers that I know of list it. I found a few trackers that listed the 40gb Dokument, but none with very many seeders. I will include a link for the Mega Folder.

      Mega Folder (75gb)


  • David

    I wonder if you could make your own pistol from the same concept…?

    • Geodkyt

      Difficult, but do-able. You won’t be copying a factory part most likely, simply because most pistol frames take MORE stress than an AR lower. But, beef up a chunky enough frame, use a steel insert for the slide rails and ejector, and I suspect you could make something that would last 100 rounds or so.

      Of course, I suspect the same level of effort would yield an aluminum pistol frame that is factory parts interchangeable. Machining aluminum is harder than aluminum, but you wouldn’t be effectively designing a gun from scratch. Also, you wouldn’t have to rebuild the gun every time you buy a Value Pack of Winchester White Box.


    Anybody have a .50 bmg upper to loan these guys for a test shoot?

  • Polymer Optics Manufacturer
    Thank you, been looking for a list like this. I will be using it quite a bit in the next several weeks. Thanks again.

  • I was wondering what is DELRIN?? Looks KOOL!! Where can I get one.

    • Geodkyt

      Delrin is simply the name of a fairly common plastic that machines really well, and is reasonably strong for an inexspensive plastic. You’ve got Delrin stuff all over your house, I’d bet, like the rollers in your kitchen drawers.

  • An easier way would be to create it in 3D and print it out.

  • cpovet

    Where can i find 80-85% .50 cal. receivers…anyone gotta clue? Thanks, ahead of time.