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The problem with shooting most 3D printed guns is that they tend to blow up. The extruded plastic components can’t take the strain caused by the expanding gasses of the powder charge, and so the gun delaminates and breaks apart. One enterprising young man from Pennsylvania thinks that he has the problem licked. His solution: specially-designed ammunition . . .

From Wired:

Michael Crumling, a 25-year-old machinist from York, Pennsylvania, has developed a round designed specifically to be fired from 3-D printed guns. His ammunition uses a thicker steel shell with a lead bullet inserted an inch inside, deep enough that the shell can contain the explosion of the round’s gunpowder instead of transferring that force to the plastic body or barrel of the gun. Crumling says that allows a home-printed firearm made from even the cheapest materials to be fired again and again without cracking or deformation. And while his design isn’t easily replicated because the rounds must be individually machined for now, it may represent another step towards durable, practical, printed guns—even semi-automatic ones.

Michael’s brainstorm is to rely on the metal of the ammunition’s case to contain the gasses instead of the surrounding material of the gun’s chamber. It’s a nifty idea, and seems to solve most of the problems that plastic 3D-printed gun makers are facing with their designs.

Essentially the ammo becomes a self-contained unit capable of doing all the work of actually forcing the bullet forward. All the gun would have to do is aim the cartridge and set off the primer. Taken a step further, someone might start producing a round such as this with a longer case length and perhaps even some rifling, producing a drop-in chamber, barrel and projectile all in one package. That should make the ATF happy, no?

Life, uh, finds a way.

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    • No joke.

      The first thing I thought of when I saw this was, “Oh, now we have a legitimate conversion method for those cheepo plastic flare guns.”

      But on second thought, maybe not.

  1. Hmmmm.

    A neat idea.

    And one that will cause the pearl-clutchers to lose even more sleep at night.

    For that reason alone, I like it.

    As for rifling the case: That could be done with a broach and a press. The trouble might be that there’s not a lot of length in a reasonable-length case for the bullet to stabilize, and there’s going to be some blow-by if the bullet doesn’t obdurate the bore before it leaves the mouth of the case.

    Still, this is a very ingenious idea, and I give this young man full props for creative thinking. And yes, it could be easily replicated by anyone with even a benchtop lathe. Lots of people used to have light lathes in their basements. Southbend 9’s and 10-K’s and the like were in abundance. Owing power tools is a habit that Americans should re-acquire.

  2. I don’t like the idea, because it presents a safety hazard in storing ammunition.
    With regular ammunition, storage is not a problem. If the rounds catch fire, there is no danger to your neighbors or firefighters. The cases simply crack and any projectiles tend to be pieces of the case. They can’t even penetrate drywall.
    With these rounds, a fire could possibly send a round into your neighbors home, which is dangerous.
    It would be as if every round were the same as a loaded firearm.

    • That’s probably not an issue.
      Mythbusters tested something similar enough. They were testing storing guns in the oven, and turning the oven up until the round fired. Because the guns were not secured to the oven rack, half the energy went into pushing the gun away, and the bullets were slow and unstable. When they secured the guns to the rack, the bullets were straight and lethal.
      So if you store this ammo without something solid supporting the case, it’s not likely to do much harm past the container you store it in.

      • You are really, seriously missing the point.

        THESE babies are different. The shells are *intended* to be mini gun barrels, basically. They take the pressure so that the plastic gun doesn’t have to.

        Therefore, in a fire, each of these is a loaded single-shot gun.


        • You’re not very clear on Newton’s 3rd law of motion, are you? If one of theses cooks off, the energy will split with equal momentum going into the case and bullet. Basically, you get neither part going fast enough to do anything.

        • FWIW, most of my ammo isn’t sitting around loose. It’s in boxes inside of other boxes, usually on hard surfaces. Were one to go off for whatever reason, the case may very well not have any ability to move rearwards whatsoever. If the energy doesn’t blow out the sides of the case or expand it so much that it doesn’t actually propel the projectile very much, it’s going to fire that bullet. In a case like these ones, designed to be cartridge, chamber, and barrel in one, it’s going to achieve velocity and direction just like the design is intended to.

      • Who stores rounds loose?
        If I had rounds that caught fire, they would be supported by the concrete they are laying on. There would be no backward momentum to absorb energy.
        Sure, a single firearm laying on the ground and going off much of the energy would be diverted to moving the firearm, but the these rounds would often be placed against something unmovable.
        We don’t need to give people a reason to place limits on ammunition storage. Regular ammunition can be safely stored in an apartment, these apparently could not be.

        • The energy would divide among all available directions, not just forawrd/backward. This is why bullets are fired from barrels, and generally not in free air with only a secure backing.

          The thicker casing of these rounds is to prevent the case/printed firearm from catastrophic failure, not to replace the forward-focusing force in a barrel.

        • If you’re afraid you will “give people a reason to place limits on ammunition storage” with these then you are completely missing the point of the whole project and should stay away.

          (hint: this technology is all about getting around those people altogether)

      • steel cases expand just fine, and can be overpressured, causing all the problems you get when you overpressure brass. steel usually has a laquer or poly coating to preserve the case and lube the extraction process.

      • Steel cases expand just fine, and they split if the case isn’t supported.
        You have 5,000 rounds of steel case ammo in a fire, and again it cooking off is not a danger to anyone.
        Set those rounds in something actually meant to contain the energy, then you have an issue.

    • Before you get all breathless, consider first that these will probably not be all over the place for 30 years even if they get popular very fast.

      Second, consider that a lot of gun owners with home defense guns DO keep loaded guns in their houses. I do.

      So… what’s the problem again?

    • You set off rounds in a fire, the heavy part will stay (relatively) still while the lighter goes flying. So it’ll send heavy steel cases popping off in all directions while the lead projectiles stay in the fire.

    • His design isn’t that much different from gas seal cartridges (like the 7.62x38R). Those cartridges have the projectile seated completely inside the mouth of the case. Without a barrel to focus the energy, they wouldn’t have enough power to do much harm. All the pressure would dissipate as soon as the bullet left the case. If you’re smart enough to store you ammo in a security cabinet or similar durable metal container, you don’t need to worry about the bullets going stray in a fire, unless of course you have them in a loaded gun.

  3. Ya’ll ever see how thick the steel is on a firearm chamber?

    Maybe that ammo will work if the bullet is .22. Ya need a certain thickness of metal to contain the forty-ish thousand (or more) psi of internal pressure generated inside modern firearm chambers. Making the cartridge case a little bit thicker ain’t gonna do it.

    Also, high pressure exists so long as the bullet resides in the barrel. Not sure having only an inch of “stronger” is going to do much.

    Not trying to poo-poo the idea; I hate being a naysayer. But I don’t think this “problem” is so easily solved. I welcome the chance to be proven wrong, though, and would love to see the real-world (or even lab) testing results.

    • The idea would be that this case actually is the entire barrel and when the bullet leaves it, it’s also leaving the gun. .380 ACP is 21,500 psi max. Keep in mind that this steel case will be surrounded by some polymer as well, and it only has to hold up for a single shot. A normal gun barrel is designed to withstand tens of thousands of rounds. The amount of steel around the chamber on some perfectly stout and reliable .380’s I’ve shot is extremely thin (like 0.035″). I can see this working.

      That said, I think it would be much, much easier to simply install a barrel insert into your 3D printed gun. A metal sleeve that’s pressed or screwed into the polymer. There are lots of .22s on the market like this, in fact, with extremely thin steel barrel inserts pressed into thicker aluminum or plastic or carbon fiber shrouds.

      • “The idea would be that this case actually is the entire barrel and when the bullet leaves it, it’s also leaving the gun. “

        So, a ONE INCH barrel? That’s kinda next-to-useless, don’t you think?

        Haven’t Cody’s designs centered mostly around AR platform .223? That’s what I was basing my comment on…RIFLE cartridges. So, let’s say someone DOES make a .380 with a one inch barrel. It won’t win a lot of hearts and minds is my read.

        Points to the guy for creative thinking and all, but like I said…I’m skeptical of this while it’s in the vaporware stage. When I see some real data I’ll be more than happy to issue my mea culpa.

        • Look at the ballistic performance of the S&W snubbies with 1.875″ barrels, and a cylinder/frame gap to boot.

          Federal 125gr HydraShoks are doing over 850 fps.

          OK, so we gut off 0.875″, we’re probably down to 700 fps. It’ll still be enough to kill someone at bad-breath distances.

          Want to increase performance while decreasing pressure? Move to a fatter pill – like a .45.

    • Wasn’t there something in the movie about WTC 7 that suggested that the weapon of one of the officers trapped beneath the rubble of WTC 7 had rounds cook off from the heat? I didn’t believe that part.

  4. “The problem with shooting most 3D printed guns is that they tend to blow up. The extruded plastic components can’t take the strain…”

    Nick, if the guns are 3D printed then they are not extruded. That’s a different process. Extrusion is what a little kid does with a play-doh press. It’s how most pasta and Twizzlers are made.

    • I would probably describe the process by which the softened/melted plastic is squeezed out of the ‘writer’ tip as extrusion. Layer by layer of extruded plastic comprises your end piece. At least most 3D printers I’ve seen seem to operate via this method.

      EDIT: hahaha, okay I went to the MakerBot site to see how they describe the process, and I said “writer” but they actually call it “the extruder.” Check out step 1:

    • One of the great (and also terrible) things about the english language is that we make it up as we go along, and change definitions by popular usage. Squirting thermoplastic in precise positions to form an object has sweet FA to do with extrusion.

      “Extrusion” is a defined manufacturing process, and decidedly not what a 3D printer does, no matter what some marginally literate hipster at MakerBot wants to call it. From da Webster…

      “Process in which metal or other material is forced through a series of dies to create desired shapes. Many ceramics are manufactured by extrusion, because the process allows efficient, continuous production. In a commercial screw-type extruder, a screw auger continuously forces the plastic feed material through an orifice or die, resulting in simple shapes such as cylindrical rods and pipes, rectangular solid and hollow bars, and long plates. In metalworking, extrusion converts a billet of metal into a length of uniform cross-section by forcing the billet through the orifice of a die; aluminum is easily extruded. Formed sheet aluminum is used for opaque curtain-wall panels and window frames.”

      What a 3D printer does is properly named AM or “additive machining”. Period. Whether done with photopolymers, laser sintering, or hot drippy thermosplastic.

      • “…resulting in simple shapes such as cylindrical rods and pipes, rectangular solid…

        I dunno. Sounds like many of the 3D printers extrude polymer in cylindrical or rectangular solids and, by the process of additive machining, build up a 3D part with it layer by layer. The part itself is not extruded, but it’s made from extruded plastic. Laser sintering and other methods definitely don’t count as extrusion in any possible way.

        • How does that even make any sense? Extrusion is defined as forcing something through a die to make the finished product. Once again, 3D additive machining has nothing to do with that.

          What you “feel” means shinola from shite. That your lack of knowledge and education shows H2O2 as ‘basically H2O’ is not my problem. Seriously, get an 8th grade education, because that’s where this is at and you can’t even keep current.

        • Machining is any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process. So what exactly is an additive material-removal process?

        • Riiight. So, wikipedia select-o-quote much? Had you actually read (or quoted) the rest of the para, you would see that it does fit the definition I posted…

          “Machining is any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process. The many processes that have this common theme, controlled material removal, are today collectively known as subtractive manufacturing, in distinction from processes of controlled material addition, which are known as additive manufacturing. Exactly what the “controlled” part of the definition implies can vary, but it almost always implies the use of machine tools (in addition to just power tools and hand tools).”

      • In response to your comment below, by that reconning an extruder at a factory stops being an extruder when the extruded material is fed into another machine for further work or assembly. A coper wire extruder is not an extruder if the wire goes directly to a machine that adds insulation or creates windings. The definition you posted matches perfectly with what most 3d printers do, the bit about an extruder only producing finished a product is your own fabrication and has nothing to do with the accepted definition.

        • “In response to your comment below, by that reconning (sic) an extruder at a factory stops being an extruder when the extruded material is fed into another machine for further work or assembly.”

          It does not mean that, by definition. Please, go re-read the quote. Read the words out loud. Whatever works for you. Squeezing the metal/plastic/playdoh out into the final shape the material extruded will be is the process of extrusion. That’s all. Coating the extruded shape, bending it, whatever are separate processes. Which all may be performed on an ‘extrusion’ after it has been extruded.

          The final shape is a gun. The thousands of droplets that make that final shape are not extrusions, they are thermoplastic squeezed through a nozzle and placed by CNC. The only way that gun part is an ‘extrusion’ is if it arrives finished after that nozzle shoots plastic through a die.

      • Brother, I’m afraid we’re fighting a rear guard action on language any more.

        I’m still fighting the good fight over the term “billet,” and I’m so not winning, either.

        • I’ve got your back on ‘billet’ my friend… (Not that it will help, I fear this battle lost.)

          Sadly, ‘Idiocracy’ is becoming far too real, far earlier than I’d have hoped. Sanctioning ignorance and outright nonsense, is no way to run life.

    • Correction: Fused Filament Fabrication 3D printers do in fact extrude the plastic (usually PLA or ABS) layer by layer to form the object. These are the cheapest forms of printers as well, meaning they’re the most common. In fact, a decent one can be purchased on amazon for well under $1000. You are correct however when it comes to SLS (Selective Laser Sintering) machines, which use a laser to fuse tiny particles of plastic layer by layer. These machines however usually cost more than an car so they’re not as common.

      • Nick, Soooo, you’re extruding ketchup when you squeeze it out of the bottle to make a smiley face on your burger? Seriously?

        Additive Machining is NOT Extrusion. Please learn what the definitions of the processes are. What is coming out of that orifice is not the final shape of the item. I posted the real definition up a few quotes. Please read the definition, it’s right there.

        Or, are we now going to call blow-molding extrusion too? Because using your ‘logic’, it would be. It involves melted plastic squirting eventually into a defined shape after all…

        • Yes, machinists use “extruding” to refer to a specific process, but that in no way means that is the ONLY definition of the word. From the 1828 Webster’s Dictionary, the first definition for “extrude” is “To thrust out; to urge, force or press out; to expel;” So, yes, one does extrude ketchup from the bottle, assuming it is from a plastic squeeze bottle and not from a glass bottle which would involve pouring. Some words have been hijacked and redefined over the years, but on the other hand, some words simply have multiple meanings. Please don’t confuse the latter case for the former.

          (1828 definition was used to ensure that the meaning had not been redefined by modern misusage.)

        • We are talking about definitions in context. How is this hard to grasp? ‘Sanction’ has a variety of disparate meanings which are completely dependent on the context. I don’t care that you don’t like what the definition actually is, or that it doesn’t match your feels. No matter what your warm-fuzzy teachers told you, it is NOT alright to be all wrong. Trot your self into a manufacturing environment and try to sell your definition. Three guys who work the line will be giving you a swirlie before lunch.

          In the context of making stuff, ‘extrusion’ has one meaning, it is defined, and that is that. ‘Riveting’ in an manufacturing context has a completely different meaning than when talking about a novel. You don’t get to move them around either.

        • “Trot your self into a manufacturing environment and try to sell your definition. Three guys who work the line will be giving you a swirlie before lunch.”

          Well there’s your problem right there. You’re apparently basing your experience off of machinists who never matured past middle school. The rest of us are dealing with real-world folks.

        • From my understanding, even the manufacturers of these devices calls it an extruder, and whether they do so because of the industry standard definition or the common usage definition is really irrelevant. The fact remains that it’s called what it is, and that at least one definition of the word does accurately describe what it does. If you want to get that changed, I suggest you write to the manufacturers rather than harassing a bunch of people online who are using a term correctly, but not to your liking.

          (Sorry for the double-post. The Edit button didn’t update the first one, for some reason.)

        • I am basing my ‘definition’ off of the “definition”. Full stop. Regardless of the maturity of the Merriam-Webster/OED folks, it is what it is. That the guy on the floor understands what a defined process is better than some dolt “in the real world” is not the shortcoming of the guy who actually knows what the effen word means.

          Once again, I care not one whit what you want to think/feel/whateva “extrusion” is, it’s a defined process. Just like “nailing”,”screwing”, and “riveting”.

          I also don’t give two good flyin’s about anyone who calls something “turbo” when it isn’t actually turbocharged. Choose to be illiterate and stupid, it is you’re right. It is also my right to tell you that you are making yourself look like a poorly educated idiot.

  5. I see an ATF tax stamp in the future of that idea, DDERRAOWERRJPUAW “Destructive Device?, errr Any Other Weapon? errrr, Just Pay Us And Wait”.

    But I like it, makes me think you could print a Gatling gun, or a LEGO “GAU”.

    CA #NaCl

  6. That’s a nifty idea. I was thinking though, wouldn’t it be better to just machine a simple metal chamber and “bolt face” to insert into the plastic frame and use conventional ammo? Then you are talking about machining one chamber from round stock and a plate with a firing pin hole in it from flat. A semi-auto blowback action which fires from an open bolt would be super simple.

    • Agreed. Instead of this idea, just sell a barrel sleeve that you insert into your 3D printed gun. It would contain the chamber and rifled barrel, and could be cut to length. End users could design guns around it. As mentioned above, there are lots of “real” firearms that do this. Especially .22s, of which many dozens of designs have an extremely thin barrel insert pressed into (or molded inside of) an aluminum, polymer, or carbon fiber barrel shroud. Even some heavy caliber guns like some .357 Mag revolver models have steel barrel inserts inside of lighter material frames like Titanium or Scandium or whatever, that may not be able to handle the pressure, heat, or friction necessary to be used for the barrel material.

      • Or use a glock or 1911 barrel as the rifled barrel and chamber sleeve (but still go with a blowback operation, ignore the link). The only reason I don’t like this though is then they’ll use it as an excuse to regulate gun parts. Given that it’s way easier to CNC a better gun than you could 3D print and the kind of “educational” nature of these experiments, I’d rather see something easily made from stock materials available at generic hardware stores.


      • >> Agreed. Instead of this idea, just sell a barrel sleeve that you insert into your 3D printed gun

        I believe this is called “plumbing” (if you’re okay with a smoothbore barrel, which will make the ATF really unhappy, but which will work just fine in practice at handgun range).

  7. With mini-rifled cartridges, the next cool 3D printer project will be a pepperbox style gun. Why have all the moving parts and concerns about proper indexing of a conventional revolver, when you could just fire off multiples of these guys – in sequence or all at once? Sort of a pocket Screaming Mimi.

  8. The kid, Michael Crumling is 25 years old, and has set out to solve the problem faced by Cody Wilson’s (26 yrs old) Liberator. Not bad for a couple of non-OFWGs. A young man came up with a way for anyone to print their own homemade pistol, then another young man comes along to tackle the obvious ammo problems faced by a plastic firearm. We should all be celebrating the ingenuity and drive of our youths who are seeking new avenues for all to participate in our 2A right.

    • Or… We can do the OFWG thing and deride his efforts out of a fear of further restrictions on our rights we are afraid to exercise. 🙂

    • As an old, white, in-shape guy, I’m going to applaud his thinking and give him some pointers that will ease his path to success.

      First, start with larger diameter bullets. Why? Because with a larger area on which the pressure in the cartridge has to act, you get a larger force accelerating the bullet at lower pressures. The chamber pressures of a .45 Colt or .45 ACP are substantially lower than those of a 9×19 or .40S&W – the .45’s are down in the low 20K PSI range, while the 9mm is around 36K PSI and the .40 is around 38, 39K PSI.

      As I mentioned above, the rifling in the case could be broached in.

      Next, there’s the issue of getting the most performance out of the bullet in a short bore length. The bullets should probably be cast of lead, so we can pre-obdurate the base of the bullet to the bore. This is easily enough done – use good lead, make a bullet mold that allows for a start chamfer on the base, then make a fixture to help align the bullet into the case. Basically, I’m thinking that the bullet should be swaged into the case. At low enough velocities, we can dispense with a gas check and go for just lead.

      Now we get to the tricky part: loading the “chamber” and priming it. Putting a bullet on top of a powder charge in these little gems will be a tad more dangerous than handloading a conventional pill onto a brass case. Now, instead of getting blowouts and the like, we have a possibility of real pressures developing and that results in Bad Things happening. I think that the cases should probably be primed last, to increase loader safety.

      As I’m thinking about it, if we wanted to push a, oh, 200gr lead pill at useful (700 fps, give or take) velocities. Eh, a few grains of Bullseye or Unique powder oughta get us up there without taking up a lot of room. That amount of powder could fit into about 40% of the length of a .45 ACP case, which means if we had a 1.5″ OAL cartridge, we have a bit more than an inch of actual bore length.

      This is all off the cuff, as I need to go do something else today. But the idea has merit.

  9. If each round serves as the barrel I guess you no longer have to clean the barrel of your guns. Things just got easier if you are a 3D printed gun owner.

    • Metalstorm was a gimmick posited as a solution looking for a problem, and is long out of business.

  10. Or the 25year old could stamp simple machine guns or shotguns in his shop. Like WW2 grease guns or the Kyber Pass AK cobblers. Seriously if you’re looking to bypass the ATF it’s gotta’ be EZ for the highly skilled 🙂 What Don said…

    • My thoughts exactly. The answer is, I don’t think it is that much different, just that the intended use of it is. The Nagant case was used to facilitate a seal between the cylinder and barrel, this is to protect the weak plastic frame of the gun.

  11. I think some of the discussion misses the point. This is an advance. there will be more. if you look a the scientific and tech papers on 3d printers the polymers being used in 10 years maybe an order of magnitude stronger than those in use today. In 50 years it is likely we will have polymers much stronger than steel.

    My dad worked with a computer the size of a large house with less than .03% of the processing power of my iPhone.

    People cannot envisage technology. I remember working on the Hll when all the experts said no home use would ever need more than 300 baud speed because no one could read an ascii stream faster than that — as if we would use our computers like teletype machines

    Whatever the solutions are, sleevees that can fit inside a barrel, sleeves as part of the ammo, eventually rifled polymer barrels that are stronger than steel, they will come. I tis also likely you will be able to have a chemical machine equivalent to 3d printer that can do simple chemistry, including making smokeless (or better) and primer material..

    The real less is that in 20-30 years individuals will be able to make MORE leathal robust and longer lasting firearms at home than normal firearms on the commercial market today. It makes gun control the ultimate luddite movement, and the distraction from the real causes of crime and violence that the gun control movement insists on ignoring, even more troubling

    • Not to rain on your parade here, but people really need to quit making comparisons between the rate of growth of computing power and much more fundamental issues of science (as opposed to engineering) in such areas as material science, battery technology, etc.

      I’ve seen the same argument made for battery capacity/weight/recharge rates, energy efficiency in engines and flying cars.

      Material science isn’t going to have too many order-of-magnitude advances. That’s what we’re talking about when we talk about computing power – “order of magnitude” (or “OOM” to engineers/scientists) improvements – ie, a factor of 10 is one OOM.

      Example: The first computer I programmed was a PDP-11/03, it was the size of a dorm room refrigerator and it had the processing power of a little better than a TRS-80. Today, my iPhone 5 dwarfs that PDP-11 (and every PDP-11 in DEC’s product line). We’re talking actually about multiple orders of magnitude increases in computing power/storage capacity/etc from that PDP-11/03 to an iPhone 5; the PDP-11’s addressed a maximum of 64KB of memory (with up to 4MB available through a paging/segmentation scheme). Let’s use the 4MB as the top end of memory capacity for the architecture. My iPhone can address 64GB. That’s 16,000 times as much memory. The CPU’s are so absurdly different, it’s hilarious: The PDP-11 was a 16-bit architecture, The A7 chip in a iPhone 5 is a 64-bit architecture, with two cores on the same chip. Probably eight orders of magnitude difference in computing speed.

      That sort of advancement isn’t going to happen in material science, polymer or no. We’ve had remarkable advances in material science, but almost no single OOM advances, never mind four+ OOM’s. To make even a single OOM improvement in material science, you need to make some breakthrough discoveries at the molecular level – ie, fundamental blue-sky science, not engineering.

      Same deal in batteries. Electric cars won’t be a viable replacement for gasoline/diesel powered vehicles in general use (as opposed to tight urban driving distances) until we see about two OOM improvement in storage capacity. To make that improvement, you need to come up with a complete new battery chemistry where the fundamental chemical reaction is storing and releasing much, much more energy than the battery technologies extant.

  12. I think this could be done a lot easier bY just taking long cases such as a 357 mag casing, dropping a small charge(.380ACP equivalent), and seating a light weight bullet way down in the casing. It would be quite achievable for just about any pistol caliber. 327mag with 32acp load, 357 mag with 380ACP load…

  13. Considering the heat from firing these 3d printed guns melts the barrel slightly and causes the case to stick, requiring the use of a rod to ram out the casing, why not make muzzle loading 3d printed guns? They would take just as long to reload as current 3d printed guns if you use paper cartridges and would have the advantage of allowing the designer to specify exactly what load to use in the gun instead of trying to design a plastic gun around the high pressures of modern ammunition.

  14. This sounds like a variation of a Russian assassination cartridge that used a captive piston to push against the bullet, resulting in a near silent firing port.

    The pistol was a two-shot derringer type. The bullet used was from the M43 7.62×39 cartridge to distract any investigation. The cartridge contained a small amount of propellant, the piston, and the bullet. The bullet was recessed into the case. On firing, the gas from the propellant expanded and pushed the piston, which in turn pushed the bullet. The piston stayed captive to the case but the effect was to dampen the report and also keep any propellant residues inside the case. The velocity of the bullet was said to be low, but adequate for close-range assassination.

  15. Para made a Mod85 paintball gun back in the day. Not sure if anyone remembers it, but the same idea was used there. The actual projectile is housed deep inside the casing (difference being plastic casing).

    Not sure if anyone even cares about the casing patent anymore, but you might want to check into that as well.

    The Mod85’s were awesome and wildly dangerous. 1200 RPM, (WHHHAAAAAAAPPPPP!!) Full auto paintball gun, that was actually a MAC-10 with a different barrel and recoil spring, LOL

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