DIY Cast AR-15 Receivers Are More Interesting Than Expected

For some reason the US News media decided on the AR-15 as the poster child of guns that should not be allowed to be made for, or sold to, the consumer. The words still out on the regulation, but, in a very American response, a whole market sprang up around people saying, “Well, then we’ll just make our own AR-15.”

Ordinarily, we wouldn’t cover this sort of thing, but the work [AR-15Mold] is doing is just so dang interesting. They sell a product that enables the home user to cast an AR-15 receiver out of high performance resin. In the process they made a really informative three part video on the casting process.

A lot of people are interested in the product, and having fun with it. In this two part video series, [Liberty Marksman] cast their receivers and test them to destruction. In one video they see how many rounds they can fire out of the gun before it breaks. When it breaks, they excitedly tear down the gun to see where it failed.

It’s quite a bit of fun to watch. Videos after the break.

 

186 thoughts on “DIY Cast AR-15 Receivers Are More Interesting Than Expected

    1. Welcome to the most commented post on hackaday this week.

      Protip: Hackaday is ultimately funded by ads and page views. By commenting on this post, you are personally giving Hackaday at least double the number of views, thereby encouraging more clickbait and needlessly controversial articles.

      Edit: replies to me will be deleted. Also, I can edit my posts.

    2. Won’t say it’s unconstitutional or illegal, but it’s certainly not interesting.
      Homemade or otherwise, get over your AR-15 and get over yourself. It’s the universal firearm of compensating for something, and you wish the feds cared even 1% as much as you do.

      1. It’s a fun rifle that is easy to accessorize and pretty cheap to shoot. Why wouldn’t it be popular?

        Personally I would like a AR-10, none of that puny 5.56/.223 for me.

        1. It’s also relatively easy to convert to a full-auto assault rifle.

          If the “black military rifles” were somehow more powerful over ordinary rifles, or offer some tactical advantage against people, there would be a reason to ban them form civilian use. If on the other hand there’s no advantage other than the fear factor and posturing, again there would be no need for the guns and it would be just better to not foster that kind of a gun culture that is based on showing off and intimidating other people with guns. Point being that guns can be abused even if they’re not fired: what’s the difference between a redneck “militia” with AR-15s “exercising their legal rights”, and an inner city thug gang patrolling the streets?

          But ultimately I think it’s just a game piece in the constitution vs. control debate and nobody really knows why they need them or not.

          1. No one that actually wants to hit anything and not waste ammo uses full auto. They may be fun, but that’s about it.

            Yeah, the people that open carry are idiots but that is such a tiny minority of the people that own ARs.

          2. Well, it’s “relatively easy” to convert any semi-automatic weapon to full-auto if you have the tools and the know-how.

            And the difference is when did you ever see a redneck militia with AR-15s hold up a gas station, demand protection money, or do drive-bys into a crowd of people?

            Either way, it’s an interesting idea. I still don’t think I would trust any plastic or resin molded firearm unless I had no other choice.

          3. Full auto has its uses if you use it right. Single rounds in the distance, full auto in very close combat in trenches and around corners, fired in short bursts. Spray and pray with every fifth round a tracer against helicopters – but that’s only effective if there’s many people shooting the same target.

            In civilian use there’s no point – unless you want to stage an uprising.

          4. Open carry while walking in the woods is okay. People open carry up here in northern New England all the time and nobody cares except in the newspaper.
            The people who wear a rifle slung over their backs just to show that they can make the rest of us look bad.
            Most of us don’t walk around in camouflage with an NRA hat. Most 2nd Ammendment Enthusiasts CC with a permit (if required); use a .9, .45, or a .22; and hope that they never ever have to draw their weapon.

          5. nobody really knows why they need them or not? In many ways it’s not a need as much as something I want and enjoy. No different that a new electronics gadget or a motor vehicle, many of which are not practical; but, are something any ethical and moral free human should be allowed to own and safely use.
            And for notarealemail below; I assume you meant 9mm and not.9, which would be one massive cartridge at twice the size of the .45 ACP.

          6. Almost EVERY gun is relatively “easy” to convert to a full-auto if you have any sense of how guns work. The AR-15 isn’t some magical device that enables your average idiot to start a revolution. Most people who would try to convert one are more apt to injure or kill themselves than succeed.

          7. Its actually not easy to convert an AR15 to full auto, the BATF makes it difficult to do intentionally. Its only easy to convert a semi to full IF you posses the ability to just make a full from scratch anyway.

          8. It is any easy way to go to prison. But I wonder. If it is so easy, why do the gangs not do it? When was the last time you heard of a shooting with a full-auto – outside of a Hollywood set?

          9. @It’s also relatively easy to convert to a full-auto assault rifle.
            No it’s not. They deliberately designed the AR-15 so it can’t fit the parts from a select fire version. You can make it “auto,” but it’s a horribly unsafe and ghetto kind of auto that even idiot rednecks know not to mess with. There are less dangerous and more fun ways to land yourself in federal prison.

          10. Lets address the last point: what is the difference between the “militia” and a inner-city thug? For the most point the militia is no real threat to anyone except as one of the new “standard villains” for TV shows. On the other hand, the “inner city thug” wants your wallet, and will shoot you for such infractions as wearing the same color he is.

            No whether they are compensating for the size of their junk, that’s another matter. I have a single shot .22. No sure what you’d make of that.

          11. “It’s also relatively easy to convert to a full-auto assault rifle.”
            That violates federal law and makes the rifle unsafe if not done right.

            “If the “black military rifles” were somehow more powerful over ordinary rifles, or offer some tactical advantage against people, there would be a reason to ban them form civilian use.”

            Actually, the opposite is true. In United States vs. Miller (1939) the supreme court allowed the banning of sawed-off shotguns precisely because they have no redeeming military value. In its decision, the court was saying that the purpose of the second amendment is for citizens owning guns that CAN be used for military uses. That is the very purpose of the second amendment.

            ” If on the other hand there’s no advantage other than the fear factor and posturing, again there would be no need for the guns and it would be just better to not foster that kind of a gun culture”
            Did Rosa Parks “need” to sit at the front of the bus? It’s no government’s business to decide that because a gun is “scary,” it should be limited. That is very antithetical to a free society. I don’t like the northeastern pompous liberal culture; but do not seek to ban it.

            “. . . and intimidating other people with guns. . . ”
            Here, you have struck on something. Every state defines assault as placing someone in fear of being harmed. Brandishing a weapon is illegal and constitutes assault.

            “But ultimately I think it’s just a game piece in the constitution vs. control debate and nobody really knows why they need them or not.”
            I certainly do know why I need the weapons I have. Self-defense. In my private home, I need weapons for the same reason I need them at work in federal law enforcement.

          12. I need them for the same reason; because like it or not, we are all really on our own, with law enforcement generally arriving after the fact to determine what happened and by whom. As I tell students in my classes. You can call 911 as long as you remember that when seconds count, help is just minutes away. In the end self reliance is the key, and for a site like this I would assume the culture would lean that way, as in; I’ll do it or make it myself thank you.

          13. “Did Rosa Parks “need” to sit at the front of the bus? It’s no government’s business to decide that because a gun is “scary,” it should be limited.”

            That’s a pretty bold analogy.

            Posturing with guns in public is more like shouting fire in a crowded theater than going against systemic racism. The whole gun thug tactical camo assault rifle scary look is just macho games, kinda like biker gangs with their vests, and all it does is make it more difficult for the public to tell actual threats from posers. That in turn makes the public more paranoid and confused about who the bad guys really are, which leads to escalations of violence with guns, and incidentally sells more guns.

          14. I used to think it was “relatively easy” too. Until I built a few. Including a couple home-milled 80%ers.

            it is not “easy” to get a closed bolt semi AR receiver to reliably cycle on auto without the same amount or more work than converting any other weapon. In fact, “easier” might be using the AK pattern.

            Of people with the licensing to legally try this, most get serious jams if not out-of battery failures. you gotta slow the cyclic rate, deal with bolt bounce, AND still get a reliable auto sear which does not pin up properly in a semiauto receiver.

            It’s much easier to convert a Glock pistol to spray and pray.

            short version: reliable autofire is tricky. There are many more easier weapons one could do, and by the time one puts in all that effort, they could pretty much build from scratch. If those with criminal usage intent (as opposed to constructive or possessive intent-i.e. “I want one but don’t wanna pay thousands for permits”) want to waste all that time and money “converting” an 80%er that will probably blow up on them or jam irrecoverably half a magazine in, more power to them. Darwinism in action.

            It’s still much cheaper to get your gear from out of the country. the sheer volume of contraband and “undocumented” individuals allows for plenty of hardware to come in that requires no conversion at all.

            And for your strawman, the biggest difference between a “militia” and “inner city thug groups”? Media makes sure ANY “milita” member with a felony record is pretty well exposed. Most “open carry advocates” have a completely clean record. Your average “inner city thug” has a significant juvenile and adult police record consisting of a felony or two making it ILLEGAL to possess a weapon. You wouldn’t be a “thug” if you didn’t have a record, you’d simply be a concerned citizen who’s living in the “inner city”.

      2. As somebody from a country where guns are banned, this is certainly interesting, i can see this (‘printing’ gun parts) changing gun laws worldwide within the next decade or two. (after all, ‘when any random fool can print a gun’ anti terrorism peeps will have a field day and it will suddenly be normal for police outside of the USA to carry rifles, meaning criminals will more often carry ‘better’ firearms aswell, which in turn increases demand of people wanting to carry a gun to protect themselves, and from there it will just grow until every mayor country has guns all over)

        1. This stuff is only a problem in the US because you can legally buy every other part of the gun, and boxes of ammunition freely – no licenses or checks anywhere. Elsewhere in the world, it’s not going to easy or cheap to print a useful gun barrel/breech or to get ammunition for the gun without a huge risk of getting caught.

          Even obtaining chemicals for making black powder can be difficult, because they just don’t sell stuff like tree stump remover made of pure KNO – precisely because people made car bombs out of it and now it’s either cut with other stuff or regulated and reported to the police.

          For example:
          https://en.wikipedia.org/wiki/2013_Santa_Monica_shooting
          Guy was prohibited from purchasing a firearm, so he built his own AR-15 out of legal parts, milled his own lower reciever, and went on an arson-and-shooting spree across town.

        1. This is Jim’s wife. Shortly after posting that, he was rounded up an sent to a reeducation camp. First will be desensitization training consisting of repeated listenings Ethyl Merman’s “God Bless America”. Next he will be required to learn how to salute a flag without rolling his eyes. Finally, he will masturbate using gun oil as lube in order to form a positive association between guns and pleasure.

    3. So you are that pot calling the kettle black by bring up any possible debate first. Beyond that you are a danger to yourself. many of those you dismiss as anti-Constitution pussies own fire arms, able to hit what they are aiming at They also under stand that the first President of the US didn’t believe that the militia mentioned in the second amendment wasn’t about ad hoc citizens militias formed because of how that group interprets the US Constitution. President George Washington disarmed such a militia. In the event the shit does hit the fan, act on using ill-conceived notions could get one hurt, be careful

      1. Do you know who Washington disarmed the whiskey rebellion with? That’s right, another militia of armed civilians.

        “A free people ought not only to be armed, but disciplined…”
        – George Washington, First Annual Address, to both House of Congress, January 8, 1790

    1. Typically you use vacuum to degas the resin then pour the resin into a mold and then put the mold into a pressure chamber which pushes the resin into all the nooks and crannies. You can pour while the mold is in a vacuum chamber but the setup is a pain and there is usually no noticeable difference.

    1. There are two main components to an AR style rifle. The upper and lower receiver. The lower receiver is the part that the ATF considers a “firearm” and it contains the trigger, hammer, fire control, magazine release, and buffer tube. The upper is where the charging handle, bolt carrier group, chamber, and barrel are.

      It is just the name that Eugene Stoner gave the parts when he designed them.

    2. Heathkit’s flagship audio product for a while was the AR-15 receiver. AM/FM Stereo, all solid-state. Considered by some to compare favorably with the best receivers of its time. I don’t know how much of it was made from cast plastics – probably not much. The AR-15 “upper” I guess would be the walnut cabinet, while the “lower” was a steel chassis with multiple-PCB construction.

    1. Probably just cost/benefit. (particularly the polymer, since the grip would take a lot of polymer for little functional gain). As I understand it (and I’m european, so that’s “not much”), the receiver is of specific interest because it’s the part red tape is attached to. If you’re not allowed to purchase a firearm, you shouldn’t be allowed to purchase the lower receiver either – but you can buy every other component part. So for anyone wanting to take their firearms freedom to its logical extreme, this is the key part.

      Also, I mindlessly clicked the wrong link to comment on this, and clicked report instead. So for anyone trying to figure out why this was reported .. I’m just failing at multitasking. mea culpa.

      1. I was bound to be reported someday :P
        the grips are pretty cheap but it’d be a nice bonus with the side effect of giving you a test run pouring a cast before you got to the important part. oh well, just a thought for ar15mold.

    2. Grips are really easy to get and install and a really small part of the parts you’ll have to buy to take this lower from what comes out of the mold to an actual shooting gun. You’re already buying an upper, a stock, the trigger group, and a couple small pieces of metal for the magazine catch etc on the lower so the cost for machining a whole mold for an unregistered and easy to get part doesn’t make sense and would increase the cost of the molds.

  1. Whilst visiting some redneck relatives in a flyover state, I got the opportunity to fire an AR-15. The thing weighed less than the .22 rifles we used to use at boy scout camp. I’ve fired handguns that weighed less. I can’t understand why normal rifles are as heavy as they are when the recoil on that AR-15 was effectively nonexistent. I wonder how much less the thing would weigh being mostly cast from resin like this.

    1. Lots of aluminum and composites, I think the only things that are steel are the barrel, bolt, trigger group, and fasteners. Though once it is loaded it will be way heavier.

      1. I can’t speak for the ar-15, but the M-16’s upper receiver is definitely steel. I know this becuase I’ve seen spots of rust on m-16s improperly stored. The lower receiver is aluminum. If the AR’s upper is aluminum I don’t imagine it would have a terribly good life expectancy.

        1. No, it is not steel. Colt never mass produced steel M16/A1/A2 upper receivers. You were probably seeing rust from the barrel extension on the upper receiver.

        2. Nah, the upper receiver is definitely aluminum – always has been. That’s why the AR-1x family was so groundbreaking in the first place. They were the first mass produced firearm to make heavy use of aluminum and fiberglass. Most uppers are made with 6061-T6 castings, though recently some of the more boutique shops have switched to 7075-T6.

          As for the longevity, the receivers, upper especially, simply isn’t a particularly stressed part. Most of the bolt carrier’s mass and energy is dumped in the receiver extension over a short period of time, resulting in a very low operating stress. While some very early M16’s did see receiver failure under sustained full auto fire (Early Vietnam era, pre -A1 designation guns) that was remedied very quickly with a reinforcement of the the lower receiver, around the extension threads. Polymer/resin lowers, like the one in the article, often fail in precisely that same spot, just like the one in the video did. Ultimately though, a typical aluminum receiver set will outlast basically every other part – typical bolts will manage maybe 7-15k rounds, a typical chrome lined barrel, maybe as much as 30k, the hammer and sear, probably around 50k, the springs, it’s a tossup, but they’ll fail at some point. But the receivers should go strong for 100k plus, especially if you’re not using full auto – the increased sear activity of the full auto action results in the pin holes bending into ovals eventually. Many early civilian owned full auto receiver sets have that issue,after many hundreds of thousands of rounds, though it’s a simple fix with aftermarket pin sets.

        3. it’s actually trickier to find a steel upper than an aluminum one nowadays. And finding a steel lower is really expensive. Why? Because I wanted one plated in brass so I could do a wood furnitured “Henry Golden Boy” style AR. Apparently aluminum doesn’t take metallic coatings well.

    2. A bit of mass makes the gun more controllable, provided you can lift it. Very light guns are ultimately more difficult to aim because it takes just a light twitch of the arm to move it. Unsupported, it becomes spray and pray.

      A light gun is great for tactical shooting where you have to swing it around fast, but not much else.

      1. @Dax
        Yeah, weight helps reduce felt recoil, but the type and design of the mechanism makes a huge difference. An AR has basically the bare minimum number of moving parts, and almost all the bits that do move are inline with the barrel, resulting in recoil that goes straight back into the shoulder. It makes for a very easy to control. Wish I was clever enough to design something that slick.

    3. My aluminum DPMS AR has less recoil than my carbon fiber Bushmaster. Neither have any real recoil given that the .223 Rem/5.56 NATO round are basically just souped up .22LR rounds. An AR-10 firing a .308 round has much more recoil due to the power of the cartridge being fired.

      Anybody that believes the FUD that the .223/5.56 round is “High Powered” needs to do a bit more research.

      1. Although they may not be “High powered”, they do penetrate much farther than alot of other rounds. My 5.56 green tips will penetrate deeper than any default 30.06 or 300 Win. mag.

        1. I read somewhere that the updated 5.56 NATO rounds (from that overhaul they did under the pretense of making a more environmentally friendly round) actually penetrates hardened steel better than 7.62 NATO. And 5.56 has always left a wider permanent cavity in meat targets. The field of internal ballistics is basically voodoo and I don’t understand it one bit.

      2. That’s funny, my AR-15 has more recoil than my AR-10, but then my 15 is an 18 inch M4 style, and my 10 is a 24 inch barrel with adjustable gas port, so the weight of the 10 helps reduce recoil, and not having it over-gassed helps too.

          1. Surely a supersonic .45 ACP wouldn’t be genuinely .45 ACP? I’d have thought there’d have to be at least a +P stuck on there, at which point we’re not really talking about the same round.

          2. Well the .45 ACP that are supersonic uses lighter bullets and hotter loads. Still are sold as .45 ACP. So as usual it depends on one defines the gray areas :)

        1. I guess it depends on your definition of “regular .22”. All of the thousands of rounds I shoot typically comp at 1200 FPS or better. I shoot some specific subsonic, which with a suppressor is whisper quiet. Even at the lower velocity the ones I generally use (Aguila ) while more quiet still function my AR’s and 10/22’s. There seems to be a lot of disinformation and assumptions being made here; but, I’m used to that.

      3. I can vouch for that fact. However, with the proper barrel and muzzle brake my .308 has less recoil than some of my 5.56 rifles. Of course, that makes my .308 a sniper class weapon used exclusively for removing feral hogs here in Texas.

      4. Anybody that thinks .22LR and 5.56 NATO are related have no clue about weapons or ammunition. Really, it is so profoundly stupid that I think you never fired a gun in your life…

        1. He’s talking about caliber. 5.56 NATO is .223, very close to the .22 long rifle. The .22, from Wikipedia: “SAAMI specifies a nominal bullet diameter of 0.2255 with a tolerance of -0.004, while the specified bore diameter is 0.222.[18] In practice, 0.224 or slightly larger bullets are common, with barrel groove diameters commonly around 0.223.”

          Since the 5.56 NATO is a .223; and the .22 long rifle is a .223, they are indeed very similar. The NATO round simply has a lot more powder behind it. You can get kits to convert an AR-15 to fire .22 long rifle rounds through the same barrel.

          1. the massive difference is in bullet length and weight. a good .22LR is 40 grains. the average good 5.56 is almost twice as heavy. so twice as long. Plus jacketed and not soft lead. and much much higher chamber pressures. You can shove rimfire down a 5.56 barrel but try to reverse same (even if you chambered it) and you’ll have seerious problems. It’s kinda like taking .38spl and saying it’s bigger than .357 so the bullets are “similar”-and you can feed the 357 with the 38 but reverse them (and they will fit) and KABOOM. Yosemite Sam time.

          2. Me Here,
            You certainly can and most of the shooters I know have done so. It allow significant practice without breaking the bank; while still learning to run the controls until they are second nature. The kit is basically a new magazine and bolt and interchanges in just a minute or so.

    1. If you are going to cast from aluminum you are going to have to machine the threads and stuff. With resins you can accurately cast threads and other holes. You could die cast the aluminum but that is a whole lot more expensive to do.

          1. Die casting yes, sand casting no, at least not at the tolerances you would need here. V threads of small pitch are difficult to cast in aluminum without voids since you have to rely on gravity to fill the cavities.

          2. I think that trying to cast threads in aluminum would be way more difficult than just tapping the holes afterward. I’m assuming that the point here is being able to make the critical component of an “assault weapon” at home without specialized skills or equipment. If so, then tapping a hole shouldn’t compromise that objective, since the equipment and process for doing so is cheap and simple.

            There’s still a possible strength issue, since the AR-15 lower receiver design may require an alloy rather than straight aluminum; there may still be the same stress fracture issue the polymer parts have if cast from melted beer cans. On the other hand, the failures were associated with high rates of fire from operating the firearm in full-auto mode. This makes the firearm in question an M-16 rather than an AR-15, so all bets are off.

          3. Yes, you can tap it bit for location you really need to be bore it before tapping. And the taps are not cheap, especially for what will be for most people a one use item.

          4. One can make a better furnace to melt steel or prepare aluminum alloy. Then, after cleaning, polishing and tapping holes one can anodize it at home, with some dye to make it harder and nice-looking…

          5. Casting steel is significantly more difficult that what I believe you think it is. Aluminum is pretty easy, there are electric and gas options. Either way you will still need to machine the receiver after, there is just no way around that.

      1. Or machine a steel mold shaped like this plastic one, then vacuum cast the aluminum into the preheated mold. If someone can DIY that process, I’d love to see it.

        1. To elaborate: mustard gas is the most well known name for sulfur mustard, which is an oily, viscous *liquid* at room temperature. The shells used to deliver it during WW1 would explode, spread a cloud of droplets, which would quickly settle onto the ground and anything on it. That initial cloud is presumably why it’s known as mustard *gas.*

          Sulfur mustard is a blister agent. Inhaling it is of course bad news (lol understatement) but it’s mostly about causing (agonizingly painful) blisters on skin. Chlorine gas, on the other hand, works by reacting with the moisture in lungs to…well, basically drown people in their own liquefied lung goo.

      1. Phosgene is always a danger when working in refrigeration. New guys to the trade almost always get a breath of it within their first month in the field. I did. It really, really sucked.

        1. What use for phosgene in refrigeration? It is an intermediate in chemical industries but has no use as a refrigerant. There are enough non-toxic (or low toxic like ammonia) alternatives.
          Possible source of exposure would be heating chlorine containing refrigerants, e.g by smoking a cigarette in an atmosphere containing FCKW (which are banned anyway these days because of ozone depletion). But that only proofs: Smoking is dangerous.

      2. My Dad once mixed bleach and ammonia. He thought it would be a good toilet bowl cleaner. I gave him hell for that! He is lucky the ammonia he used wad already watered-down for windows. It melted the spray mechanism.
        Always read the labels. And then ignore them anyway.

    1. Many years ago there was a paper in “The Journal of Irreducible Results” on making nerve gas from fluoridated toothpaste. Bloomberg and Clinton were not concerned.

      1. Isn’t the supposedly cult that included the guy who accused the US of using resonant explosives and fracking to cause earthquakes in Japan, before a yakuza member assassinated him on live TV?

        Seriously, you can’t make this stuff up. Hollywood got nothing on real life son.

  2. These guys can shoot well, but dont know how to clear a jam at all. Also, the suspected component for causing the jam in the bump fire test would not be the bump fire stock, it would be some part of the fire control group or safety. Obviously, these guys know nothing of the practical side of guns, how to fix and diagnose, and how to get a gun back up and running when they fail.

  3. No mention anywhere about what polymer is being used on these. From the way it burns, it looks like acrylic, but I’d have to smell it to know for sure. Since the failures they had were stress fractures next to a pin, I wonder if a glass-filled polymer would be better. Though I still wonder about the folly of making plastic parts for a machine that was designed for aluminum alloy. Seems like there should be some re-engineering involved, beefing-up the high-stress areas.

    1. yeah, i really don’t understand the fixation some of these people seem to have with making gun parts with variations of plastic.

      also, really surprised at the lack of hate-filled responses these posts usually get.

    2. Yes, the designs definitely need to be changed for the plastic builds. The more successful commercial plastic lowers are reinforced at the top near the front and rear takedown pins. Better would be a complete redesign but then it wouldn’t be compatible with existing parts.

  4. Psst, the parts that failed on this can be improved with some thin steel mold inserts that are cast into the stress points of the receiver, especially the rear takedown pin and buffer tube interface.

    1. The testing requirements were not specified, so it’s hard to say whether the buffer tube interface “failed”. The part was simply stressed to failure. The same would have happened to an Armalite lower receiver, though probably at a higher force. Not only was there no minimum acceptable force specified, but the deflection was measured at an arbitrary distance down the receiver tube, with no indication of what would be an acceptable deflection. A test is not a test unless there is a pass/fail threshold. This was just two guys messing around with the instrumentation they could get their hands on, to no purpose.

      As to the failure at the rear takedown pin, this was a clear failure because it happened during normal use of the machine (although it is arguable that full-automatic cycle rates are not normal use of an AR-15), so maybe a steel insert would help here, but I’m not convinced of that since the insert has to be anchored in the casting somehow, in order to spread out the stress.

      1. I read the some of the tests. The mounting holes stretch after a 3 or 4 thousand rounds and the fit between the upper and lower starts to get loose. The failure mode is brittle cracks when they tapped on the lowers they scraped due to air bubbles with a 2 pound hammer. The effort they put into tapping wasn’t a lot. The threaded ring for the buffer tube was the strongest part of the gun.

        If I was going to build one using this kit. I would make 2 steel inserts with holes drilled for the pins that mount the upper that have a long tail that wraps around the boss that the buffer tube screws into. The two parts that warp around the boss the buffer tube screws into would over lap each other with one in front of the the other. I wold hope the steel reinforced the holes and kept the holes from spreading and prevented the gun from breaking in the area of the trigger group.

  5. Encapsulation/Resin potting compounds used for structural builds is quite interesting. There are quite a variety of different resin bases out there and there is very little information besides the manufacture data and the MSDS sheet. I’ve struggled get get reliable information from manufactures in the past. So any testing of these products is good to see.

    as “BrightBlueJim” said, it would be nice to know the product there using.

    Also it may be helpful to vacuum the mix before pouring to remove the voids in the solution.

          1. Your bolt design would need to be very unusual to handle a necked up cartridge. I have never heard of anyone doing such a thing on purpose.

          2. The .300 AAC Blackout is a 5.56 x 45mm casing cut down and necked down for the 7.62mm bullet. It is an interesting round, allowing most of the components of the M16 / M4 / AR-15 platform to used with only a change of the barrel.

      1. That’s actually a bit ambiguous. Since its a rifle, so long as it’s designed and used solely for sporting purposes it’s not technically an AOW or DD.

          1. And it has a rifled barrel. It is possible to send the weapon and rounds to the ATF for inspection and ruling. I have done it with my M2 conversions. If they give a ruling that requires you to have a license they keep the weapon until you cough up a license. Only shotgun rounds are considered “sporting”. All calibers larger than .50 are considered Title II NFA weapons, unless antique, shotgun (with exceptions), or muzzle loaded.

          2. There have been a few large caliber rounds that are still Title II weapons, but are considered exempt. They are all bolt action custom made rifles that are considered “sporting, but unlikely to be mass produced in volume” giving them all a high dollar value and putting them out of the hands of the average person. The ruling of exemption can only be made by mailing a new rifle and rounds to the ATF firearms technology branch .700 Nitro express is one example.

          3. @comidicles
            Gauge is a shotgun term, shotguns are exempt from the 0.5″ rule. Good luck finding a state that allows hunting with larger than a 10 gauge though.

            Big game rifles are also generally exempt since they are rifles, sporting arms, and largely break or bolt action.

          4. @TheRegnirps

            Yes, but then, as now, Guage and bore are more commonly associated with smooth bore shotguns. While rifles are denoted by their caliber or diameter in mm.
            I imagine modern BGH’s use modern cartridges that follow this rule (.45-70, .300 mag, nitro express, &c)

    1. What makes that more of a gun than the AR 15? It is not practical in any way or form and for real world uses it simply sucks – but for the over-compensating crowd “power” is everything right?

  6. PLASTIC AR-15 IS WEAPON OF MAN WHO WEAR GADSDEN SNAKE SHIRT OF CHINESE SLAVE HAND SEWING, MASTURBATE ON 3D PRINTER, SHOW OFF GUN IN PUBLIC AND THINK THAT HE IS SOLDIER. THIS MAN HAVE DISEASE OF AMERICAN CAPITALIST, MAKE THING FOR NO REASON EXCEPT ATTENTION AND NEWS PAPER WRITING.

    PLASTIC AR-15 IS WEAPON THAT SAY IS NO SUCH THING AS CONCERN OF MONEY OR RELIABLE WEAPON FOR SHOOTING MANY MAGAZINE OF CARTRIDGE. IS ONLY GOOD FOR SHOW OFF AT HICK PARTY AND HIT LARGEST SIDE OF BARN FEW TIME THEN FAIL.
    PLASTIC RIFLE IS TRASH. AR-15 IS CAPITALIST RIFLE BUT NO NEED TO FUCK IT MORE.

    IF YOU NEED “GHOST” GUN WITH NO PAPERS TO PARTY INSPECTOR, THINK BEFORE SPEND. MAKE KALASHNIKOV SISTEMA RIFLE FROM OLD BARN SHOVEL. ONLY NEED HANDS AND TOOLS OF METAL. SHOVEL RIFLE UGLY BUT STILL PROUD DESIGN OF MIKHAIL KALASHNIKOV AND PROUD WORKMANSHIP OF COMRADE.

    http://www.northeastshooters.com/vbulletin/threads/179192

    1. Commie guns are cool. I own two Mosin Nagant rifles (an M-38 and a 91/30) and a Nagant 7.62 x 38 revolver. I want a Tokarev.

      But I also like my AR-15. It’s really fun to shoot. The beauty of capitalism is that I CAN own and use these weapons.

    1. castAR is not going to happen, Jeri was lured to the dark side by VC, they will keep it in ‘almost ready for release’ state until a bigger sucker comes along and pays $1B, or they run out of money :(

  7. Looking at ar15mold.com:

    1) Mold kit is $339.99.
    2) A stainless steel support brace is available that stiffens the rear of the lower receiver, for $6.00.
    3) A 60-oz refill kit for making five lower receivers is $129.00. No specifics about the polymer are given.

    1. wow. didn’t realize this form was that expensive.. from a cost standpoint, what point does this serve? according to brad’s post on cost of 80% lowers, it’s 4x’s more expensive to get started, as well as a similar price for every new one, and it’s more prone to failure

      1. I think that casting a part in urethane takes a lot less skill and other equipment to do than all of the finish machining required to complete an 80% lower. The pricing has little to do with cost of manufacturing the mold; I think it has more to do with being “what the market will bear” when it comes to making an easier option than machining. The only advantage is if you plan on breaking a bunch of these, the cost goes down with quantity. Not much, mind you, since you still have to buy all of the metal parts that go into the lower receiver, and since they’re charging about 4 times the going rate for resin.

      2. soundman98,
        I think the main point it serves is the entire premise for this site. DIY hacking. There are many projects I’ve seen here over the years that could be easier and maybe less expensive than just buying a commercial version of the same item or device; but, that fun and satisfaction you get, makes it all worthwhile, no matter the project type.

  8. What their mold needs is a groove milled around one half and a length of square O-ring rubber to fit into it so that when the mold is assembled the rubber strip is compressed a bit to seal it.

    1. In one of the pictures on their website (sorry, don’t have it in front of me), it shows a just-out-of-the-mold part, and there’s a LOT of flash. I think what they really need is a lot more screws holding the halves together, around the perimeter of the cavity. This ain’t a metal mold.

  9. Its interesting, Its a clever use of moulding. But… punching holes in things at a distance using expanding gas is not a particularly novel technology, we have been able to do that for the best part of 1000 years. It doesn’t really bring us anything new.

    Now if it solved this problem, I might be interested. https://en.wikipedia.org/wiki/List_of_countries_by_firearm-related_death_rate .. but then again, I can’t be bothered listening to the usual doublespeak drivel about “guns not killing people, people kill people”.

    Until you see the results of firearm injury, you will still all love your long metal sticks with holes in that put holes in things at a distance. Don’t get me wrong, I grew up punching holes in things at a distance, it has its place.. I enjoy rabbit stew, and the odd haunch of venison, but I have absolutely no need for an assault rifle.

    1. A)The article is highlighting home resin casting & mold making, a technology that had been overshadowed by 3D printing, not some advance in fire arms tech.
      B)The AR has as much in common with the rifle you get your venison with as it does the rifle militaries use
      C)No one is forcing you to own one
      D)The right to bear arms isn’t about hunting.

  10. Hunting riffles are used for hunting. Assault riffles are used for assault. You can protect yourself / kill with either, but a riffle designed for killing people a greater sense of power. What do you need an assault rifle for that you cannot use a hunting riffle for other than to feel powerful?

    1. Steel_9,
      The problem with so called Assault Rifles is that the name was invented by ignorant people with agendas who still think semi-auto firearms use a clip. An AR-15 is no more an Assault Rifle than a Corvette is an Assault vehicle, or a laser printer is an Assault printing press. Ignorance and agenda have driven the area of firearms ownership for nearly 50 years. In an age of nearly infinite information availability and fast search capabilities, only wanton or willful (purposeful) ignorance IMO makes any sense, so one must ask themselves, which am I?

    2. Well. . . if someone’s purpose of owning a gun is for self-defense, that someone should buy a gun designed to kill people, not squirrels. My wife owns a Mossberg 590 tactical shotgun. It’s a much better home defense weapon than a .410 with light loads.

    3. Please read the ATF’s definition of ‘assault rifle’.
      https://www.atf.gov/firearms/firearms-guide-identification-firearms-within-purview-national-firearms-act
      The media wants people to believe a falsehood.
      Hitting targets from 100 yards with a rifle is one of my few good skills. But I would never point it at someone unless someone else already has at me. Sometimes guns save lives without firing a shot.
      And user ‘Me Here’, a .410 or .22 is plenty dangerous to a burglar and is less likely to travel into another room in the house. Only one bedroom in the house? Then I would agree with you.

  11. This being Hackaday, why are 99% of all the comments about the gun??
    The interesting part here is the casting, the resin, and that the mold seam to be milled plastic.
    So, anyone have any idea on what resin they are using? Can we get this resin or similar resin from somewhere else than these guys? I for one is not very interested in ordering from these guys at all.. And as I live in Europe it will probably just get stuck in customs anyway..
    From the video this looks like a mold printed in PC+ or ABS should work. And that would make for an awesome way of making durable small boxes for projects, or any part that need a bit more strength to it.

    1. We do have a few clues to the resin being used:
      * It cures white (opaque or translucent),
      * The uncured part A is transparent amber, part B is water clear,
      * It’s a 2-part compound that needs to be mixed 2:1 by weight,
      * It has a working time of about 6 minutes, with de-mold time of 70 minutes.

      The white isn’t just due to some filler compound, since it appears water-clear when mixing.
      2:1 would be about right for epoxy, but that usually cures to a transparent amber color.
      Polyester uses a much higher ratio of resin:catylist, and cures clear transparent.
      Somebody suggested that it’s urethane, and this is probably the case. Fibre Glast makes a urethane resin that cures white at a hardness of 75 Shore D (which they compare with a hard hat). Its viscosity is low for easy mold filling. Pot life is 30 minutes at room temperature. Tensile strength is given as 5000 PSI. A:B mix is 1:1, but they have other compounds that are close to 2:1.
      Smooth-On makes a similar product, Smooth-Cast 305, that also cures white to 70 Shore D hardness, but this is a 10:9 mix.

      Another issue, when making molds, is what material to use for the molds themselves. I can’t tell for sure if the molds in the video are machined or are themselves made by casting, but my guess is casting, since there’s a product name in bas-relief, which would be a lot of extra machining. Can you cast urethane in a urethane mold (with an appropriate release agent, of course)?

      Anyway, urethane is nice for casting one part at a time, where it doesn’t matter that there’s a long cure time to de-molding, since it doesn’t require high pressure like injection molding, BUT, as you can see in the video where they stress one of the parts to failure, it can end up full of small bubbles if you don’t vacuum de-gas it. Or, they may just have mixed too much air into it – some of the manufacturers say you just have to mix slowly to avoid creating bubbles.

      If that IS urethane they’re selling with the kits, they’re marking it WAAAAY up – $129 for 60 oz. By comparison, the Smooth-Cast 305 is $85 for 1 gallon each of A and B, or about four times as much material.

    1. Any silicone based release agent works with JB Weld. I have made a few small parts with it. And it does not stick to Kapton very well, so I used it to re-bed a mini lathe once. It worked great, and was way easier than scraping the ways.

      1. Do you have any pictures? I’d love to hear about this process and why you chose JB weld. I watched a video on youtube by Stefan Gotteswinter where he used a professional compound called moglice to do the same. I wondered how the process was undertaken.

        1. I chose JB weld mainly for it’s (cured) density and filler used. Sorry, I didn’t take any pictures. I had spent about a week scraping the areas that contact my lathe bed, bluing, scraping, bluing, and so on… I guess I am not that patient a person. Anyway, out of frustration I started reading about re-bedding, and came across Moglice (as you did), and thought- Why not just use JB Weld? It has stainless steel filler in it, and it should last long enough. I have a 7X16 mini lathe from Micromark. And I will tell you, if you are in the market for a mini lathe, buy bigger! All the mini lathes are made in China and require lots of work and tuning to get them to cut steel well. I added adjustable carriage jibs, re-jibed the cross-slide and compound (lots of work), and added an inch of cross-slide travel. In the process of making these modifications, I added extra tapped holes to the top of the carriage on the opposite side of the existing holes for the follower rest. This turned out to be critical.
          So, after much scraping, I decided to just take the bearing surfaces of the carriage to the grinder, remove some material (leave it rough), clean thoroughly with acetone.
          Then I needed to create a perfectly uniform (flat and level) upper surface of my carriage. So I made short (2.5 inch) arms out of some 1/2″ x 1″ wide scrap steel. Drilled through on one end and tapped through on the other. Long set screws were set into the tapped ends (with a locking nut on them). The other ends were bolted onto the top surface of the carriage at the four corners and positioned such that the set screws could be adjusted to touch the top of the ways and set the gap height (between the bearing surface of the carriage and the lathe bed), and adjust it to be perfectly level (using a dial indicator). The jaws were removed from the lathe chuck.
          Kapton tape was adhered to the lathe bed (and anywhere I did not want the JB Weld to stick), and JB Weld was mixed and applied to the bearing surfaces of the carriage, and then it was set down on the lathe bed (close to the head stock) and pushed toward the head stock until it touched the lathe chuck (this makes sure it is square to the center line of the lathe).
          I waited three days, popped the carriage off with a bit of force (gentle crowbar work), and removed the tape.
          It works great now, no chatter when cutting any steel alloy with carbide cutters. And as it wears down I can use my carriage jibs to tighten it back up. I have about 100 hours of run time on it. I will do my tailstock next.
          I strongly recommend Littlemachineshop dot com for parts and tooling.
          Thank for asking.

          1. Wow! Thanks for the great info! There’s a lathe/mill thing at the local hackerspace with a bed that tilts .04 mm out of square when the direction changes no matter how tight the gibs are. I’ve been thinking of convincing them to let me scrape it within an inch of its life, but I don’t have the tool to get into the ways so I’ve been searching for alternatives.

          2. No problem. I had the exact same problem with my lathe. I have read that it is common with small lathes and with very old worn out lathes.
            One thing I forgot to mention-
            If you try this, when you first pull the carriage off the ways after the JB Weld has cured (I waited three days just to be sure), the surface of the JB Weld will be smooth as glass (because it was touching the Kapton). This is not good for oil retention, so I used some 600 grit sand paper and very gently roughed up the surface in a very uniform manner to allow the surface to hold some way oil. Otherwise the carriage will be very sticky, and difficult to move after it goes back and forth a few times.
            Also- Make sure you put extra JB weld on the carriage initially, so that as you place the carriage down on the ways, the extra will squish out. This will make sure you don’t have voids or uncoated areas. after it cures, you can use a file to trim the excess to make it look nice. If there are a few small voids it won’t hurt anything. It just gives a place for the way oil to sit to lubricate the ways.
            If you pull the carriage off and find large areas with no JB Weld or areas where the JB Weld was clearly not in contact with the Kapton, You can easily just mix up some more JB Weld, put it in those areas, put the carriage back on the ways (make sure the ways are still covered with Kapton), and wait till it cures.
            Ideally, the thickness of the coating of JB Weld will equal the thickness of the Kapton when you are done. But, if you use a quick change tool post with adjustable cutter height it won’t matter if you add a little to the height of the top of the carriage.

  12. You can download the plans for pistol caliber sub-machine gun built from hardware store parts that are much simpler(read as made with hand tools) and more durable than of these 3d printed guns, so why bother?

    1. I see two ways of reading an article like this:
      1) Here’s one way to make [part of] a gun – not very well, but in a way that’s hard to trace.
      2) Here’s an alternative to 3D printing for making small quantities of parts that are traditionally made of metal.

      Since I don’t have any current need any additional firearms, guess which way I’m reading it.

  13. I think this is awesome, why not take the final piece and use it to create a mold for metal? Also everyone who make their own ar resin casting should use pink or pastels maybe if guns were dolled up a bit. Lol

Leave a Reply to Rick Cancel reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.