Making a Whole Gun with CNC

Jason and I have discussed the idea of making an entire firearm with the CNC machine. Currently, he’s only made two AR-15 style receivers, which is the part of the gun that is legally considered “the gun,” but the rest of the parts were purchased as parts kits. It is lawful to make your own guns, provided you’re not doing it to sell or transfer them. If you want to do that, you’re considered in the business of manufacturing, and need to possess a Federal Firearms License. The point in the project was to show the folly of gun control, and to have a little fun in the process. While I think some progress has been made in that regard, it still leaves open the argument that the hard parts are still purchased, so clearly a hypothetical person could be stopped merely be restricting parts of guns as heavily as guns.

But really, the only thing that makes a lot of this hard is the legal aspects that already exist. The difficulties Jason has experienced is mostly just in the learning process. He’s not trained as a machinist, and has never tried this before. The goal is to try until success, and that takes trial and error in wasted aluminum and plastic. Once success is achieved, replication would be trivial, but since we’re law abiding here, there’s no need to do that. A one off success is completion of the project.

So what about making a whole gun? The hard part is the barrel. Barrels have to be a hard steel, and hard steel is expensive and difficult to machine. The law also requires pistols to have a rifled barrel. If you do a smooth barrel firearm on the scale that’s easy to do on this small mill, you generally have an NFA firearm, which you can’t just manufacture willy nilly legally. Speaking of NFA, it would probably be easier to design a simple submachine gun than it would be to design a reliable semi-automatic pistol. But again, because we’re law abiding here, that’s off the table.

The idea of doing an entire home-made CNC pistol, with equipment that is within the reach of the hobbyist, is still a pipe dream. For someone who wishes to remain law abiding, it’s risky business not sticking to traditional designs. Criminals would not have this limitation, and thus would have an easier time.

40 thoughts on “Making a Whole Gun with CNC”

  1. If you are designing a pistol, couldn’t you modify a cheap hydraulic jack to do button rifling over the length of the short barrel? I agree crafting a sinebar machine for cut rifling, while well within the possibility of a home machinist, is not as practical for a hobbyist. But it should be possible to rig up a button rifling machine, I would think.

    And you can get away with normal high-carbon steel for the barrel… …with light trap loads & subsonic 22s, at least…

    Really, though, the practical way to treat the steel for the barrel would be to machine it in the annealed state and then heat-treat it afterwards, which is definitely not something the home hobbyist wants to take on. Rifled barrels are hard.

    1. On the other hand, our founding-era forefathers were doing rifling in a blacksmithing context, so it’s certainly not impossible – even for things heftier than subsonic .22LR.

      As you say, you’re rather limited on pressure if you go that route, but I imagine the home machinist could use softer steels to make barrels in the .22-.32 range (or larger, as long as they stick to black-powder-era cartridges)…

      (Also, heat treating isn’t that hard!)

      1. It’s not that heat-treating is difficult; it’s that it requires equipment most hobbyists do not have or do not want to spend the money on – namely, the oven. The proper temperature for Vascomax C300 (a nice maraging steel that I’ve worked with) heat treatment is over 900 deg. F for six hours. I suppose you could put the barrel in a standard oven on a self-cleaning cycle; not something I’d do, though.

  2. does it have to be *effective* rifling? or can your just sorta cut long groves in the barrel and say it’s a 1 in 1000 twist rate. . .

      1. I suspect that the legal answer will be “rifled enough to make the bullet spin convincingly (since “rifled” is not strictly defined by rate in the NFA, last I checked).

        (A 1:1000 rate will probably be thus indistinguishable from un-rifled, and a “who do you think you’re kidding anyway?” matter.)

        Perhaps more interestingly, as a proof-of-concept, you could have a rifled barrel-exension at the muzzle end, to impart spin.

        This would be easier to machine, even out of hard modern steel, and let you do a hard steel barrel without rifling for most of the length.

        If permanently attached, it should satisfy the ATF as to “rifled”.

        The downside would be that naturally it wouldn’t be AS accurate – but I think it would suffice as a proof of concept and for short-range plinking or pistolcraft purposes.)

  3. The barrel is easy enough. Harry Pope made some of the finest barrels of his era from junkyard axles. They are very high grade steel, in sizes suitable for any reasonably short barrel you want. And they are already “stress relieved.”

    Those lovely Pennsylvania rifles were bored and rifled with a rig that anyone handy with tools could make at home. And unless you want some odd caliber, you would have the double advantage of not having to make your own drill – and of not having to turn that drill by hand.


  4. Sten barrels had only two shallow grooves cut into them just to speed up production, if I remember correctly. And you know how easy a Sten could be made…..

    1. Indeed; echoing the original post’s comments, I informally studied WWI era submachine gun while in high school (WWII was still a very big thing then) and there’s nothing more simple than an open bolt blowback submachine gun with an integral firing pin on the face of the bolt.

      There is a big safety issue with these, though: they need something to really reliably secure the bolt for safe condition 3 carry, otherwise the common failure mode was dropping one on its butt with the bolt then going back due to inertia, not far enough to catch the sear but far enough to strip off a round.

      1. I am given to understand the BATFE considers any open-bolt blowback firearm to be “readily convertible” regardless of any other features

        1. I seem to remember Sten kits that had closed-bolt lockwork for semi-auto operation.

        2. Ian: Well, yeah, and this is not one of their shoestring or soft primer based determinations. As I understand it, open-bolt blowback firearms really are “readily convertible” as defined by their skill + labor time metric.

          1. Since the hardest thing about an OBB weapon is to get it to stop repeating, I am inclined, just this once, to agree with them.

  5. Seems to me that the minimum standard for a barrel is that one shot can be fired accurately, without hurting the shooter, and without destroying the rest of the gun.

    Motorcycle helmets and baby car seats get replaced after one crash – they are designed to deform and aren’t reusable products.

    I don’t know metallurgy, but a single-use barrel is a lower standard of hardness than a barrel able to withstand 10k rounds.

    A derringer seems like it would be easiest to make a barrel for.

  6. Which is the harder problem? Obtaining steel rods suitable for barrels, or boring the barrel out, or rifling the bore?

    1. The latter, as I understand it.

      Steel rod stock is trivially obtained (if not necessarily inexpensive, in the hard/durable grades).

      Boring, for a pistol-length barrel at least, is also not all that hard with a decent medium-small lathe. (Rifle-length starts to require much more expensive machines and drill bits, naturally.)

      It’s rifling a hard barrel that’s tricky with common tools, is my understanding.

  7. My Father used to own a Machine Shop, and trust me, it’s not the Machines, it’s the Special Tooling and Fixtures you need. Steel of all Grades and Sizes can be order from any area that still has some Machine Shops in Business, you just have to Pay for it.

    But as Economic Factors go, you just be better off stock piling up Parts Kits and save the Building for the Receivers (and Trunions if you go AK). Yes, the Dutch made Stens during WW2, but they were built in Bicycle Shops which had all the Parts pretty much there. It would be Cheaper and Faster in the Long Run. But even then, AR Lowers are, what, a Hundred Bucks?

    Personally, I’d be looking into (FOR INFORMATIONAL PURPOSES ONLY!) what is needed for Suppressors, then Stockpile those Materials. Who knows what the Future might bring?

      1. Not to mention there’s no “proof of concept” needed, which I gather is much of what your projects are about.

  8. As others have pointed out, why not just make a manual rifling machine? It’s a nearly 500 year old technology. No reason why you couldn’t do it unless you were limiting yourself to only using the CNC machine.

    1. We could do that, but rifling was a difficult process back then. We’ve also been trying to restrict ourselves to technology that’s off the shelf and readily available, and operable by someone who doesn’t have any specific domain knowledge in gun making, engineering, or machining.

  9. BH Les +1. With over 200 million firearms in the USA, it doesn’t make much sense to CNC-machine new ones, since even during/after the Zombie Apocalypse, there will be plenty of guns.

    Stockpile ammo and/or components, prepare your “deep storage safes” for a few off-the-books arms, and if you MUST get into CNC work, make suppressors and be prepared to thread barrels to accept them.

    Urban warfare is a noisy business. When it is suppressor-quieted, the quiet ones have huge advantages, perhaps enough advantage to overcome the Zombie use of sensor tech.

    Do all of that, THEN you have prepared yourself.

    1. “and if you MUST get into CNC work, make suppressors and be prepared to thread barrels to accept them.”

      Good way to go to prison, unless you file the right forms.

    2. Learning to CNC guns is, technically, something fun to do in your spare time. Additionally, you get an unlicensed gun afterward!

      It is my understanding that one of the points of this is to demonstrate that making an entire gun from scratch is readably possible for someone who intends to do it. Sebastian has a good point, too: if you can only make a receiver, but all the parts are banned, then if you want to demonstrate the easiness of making guns, you’re going to have to make the parts as well.

      It’s not as if antis haven’t thought about this. It’s my understanding that in Massachusetts and New York State, just having a firing pin or an empty shell is a criminal offense.

  10. Barrel blanks are cheap. One rifle blank will make two or three pistol blanks. As inexpensive as good 4140 blanks are, there’s no reason to bother making them unless you really just want to know how. Even the chamber reamers are easy to replicate for someone who has a cnc lathe or novice lathe machining skills.
    In a EOFTWAWKI situation, a drilled and reamed piece of pipe would theoretically work for a barrel, but accuracy (among other things) would suffer. Check out P.A. Luty’s SMG plans as an example of this.

    Bill Holmes did a book on the AR15 and IIRC he outlined how to build one out of sheetmetal and round tubing. Not a beautiful end product, but functional.
    Gun control is indeed very dead. You don’t do anything about demand, you only increase the price of the supply.

  11. You can make a simple blowback pistol cartridge carbine fairly easily. Just use a very heavy bolt.

    To make it a semi-auto, you would need to add a real firing pin to the bolt, instead of the usual SMG firing nipple on the bolt face.

    Either spring load the firing pin, and use sear to prevent the pin from gong forward ( mauser style ignition ), or put a hammer behind the bolt.

    A pistol caliber carbine can get away with an astoundingly soft barrel.

  12. If you are in the jurisdiction if the District Court of
    Illinois it is just as legal to make a fully automatic
    firearm for personal use as any other firearm. See the
    Rock Island Arsenal case for more info.

    Unfortunately the Federal Government doesn’t follow the
    law in regards to this but you would be in the right and
    they would be in the wrong when their swat team kicked your
    door down, shot your dog, stomped your cat and killed you
    while “resisting arrest”. :-)

    1. I’ve covered that before on this blog. If you make a machine gun anywhere in this country you’re going to jail. Many many people have completely misread Rock Island because they don’t understand how the law is structured.

      Sorry to be blunt about this, but I don’t want people going to jail believing this stuff.

    2. I should clarify… what Rock Island said is that federal prosecutors can’t charge someone who makes a machine gun under the National Firearms Act, which is part of the Internal Revenue Code. The reason for this is that the government can’t prosecute someone based on failure to pay a tax that it refuses to collect.

      It can prosecute based on 922(o), which is part of the Federal Criminal Code. All that occurred in Rock Island was that the federal prosecutors picked the wrong charge, and the courts called them on it. You’ll still get nailed on 922(o), and now all federal prosecutions for having a post-86 machine gun proceed based on that criminals statute.

    3. It’s my understanding that Montana and perhaps even Utah have passed laws a couple of years ago that say, in effect, that any gun made in their States are not a part of Interstate Commerce, so Federal Law does not apply to that gun.

      These laws, though, have not yet been tested in court, and as much as I’d like to see them tested, I’m not willing to be the one to test them myself!

        1. “They are extremely unlikely to be upheld by the courts in the present political climate.”

          There, I fixed that for you.

          There’s a difference between that which is impossible, and that which is merely extremely improbable.

  13. Both Foxfire 5 and Diderot’s Encyclopedia give adequate then current state of the art directions for barrel making and most of the rest of it. For improvisation of course the Phillipine Guerilla gun works just fine smoothbore.

  14. Sebastian, why are you making a big deal about these “laws”? I thought that the teddy bear indistry was more regulated than the gun industry! :-)

  15. Look online for the “Colonial Gunsmith” video from Colonial Williamsburg. The rifling jig/machine used to make a muzzle-loader barrel is literally made out of WOOD, with slivers of paper as shims to raise the cutting tooth in the rifling rod.

    Bullets can be cast, cut or swaged from any appropriate metal alloy. Black powder can be made by virtually anyone with some basic chemical/historical knowledge. Primers can be re-built using certain types of match heads.

    Where there’s a will, there’s a way.

  16. Rifling is almost trivial. Hook rifling with the “hook” shimmed to deepen the rifling, four land and groove rifling, is simple enough to do with scrap lumber. One heavy plank for a stable spine, and a wooden cylinder with the twist cut in it is the basics of a pre 1830 or so rifling machine.

    Boring the barrel is a bit more complex but the Pennsylvania gunsmiths managed with wooden boring machines. Once the hole is started a good drill will “track true” and you either cut off or chamber the starting end of the barrel. And 36″ “gun drills” are reasonably cheap.

    The real problem may be threading the barrel and action, since that is going to take a lathe or some really strong arm work. But the Afghans use homemade treadle lathes and files to build serviceable Lee Enfields.

    If you take your time and use plenty of lubricant, some of the old timers used cold stream water to cool the barrel and flush out chips, a couple of inches at 100 yards is a reasonable expectation.


  17. I’ve been wondering if it would be possible to build up rifling with hard chrome. Wrap your electrode with a spiral dielectric that can withstand the plating solution and is thicker than the depth of rifling you want, center the electrode in a smooth bore, hook up the leads, submerge in plating solution and apply power.

Comments are closed.