3D Printing Method for Making Advanced Machine Gun Barrels Being Developed by US Army ARDEC [NDIA 2017]

Original caption: "U.S. Army Spc. Jason Williams, Bravo Company, 186th Brigade Support Battalion (BSB), 86th Infantry Brigade Combat Team (Mountain), Vermont National Guard, qualifies with an M2 machine gun at Fort Drum, N.Y., June 13, 2017." U.S. Army by Spc. Avery Cunningham, public domain

At the 2017 National Defense Industry Association conference on small arms, US Army ARDEC presented a brief on new technologies for enhancing the longevity of machine gun barrels, using 3D printing techniques. The project’s goals as stated in the presentation were to eliminate the need for spare barrels to be carried by reducing barrel temperature (especially chamber temperature) and increasing the cookoff limit of the barrel (the point at which a barrel gets so hot that rounds will fire from heat alone, without the primer being struck by the firing pin), without a decrease in accuracy or an increase in barrel weight. The team investigated two different 3D printing methods for manufacturing advanced barrel units:

To create the perfect 3D-printed barrel, the team needed to study the problem carefully, to determine which cooling mechanisms were most effective at what temperatures. This experimentation was carried out with the powerful finite element analysis (FEA) software LS-DYNA:

This experimentation allowed the design of a three-material barrel, using a cobalt superalloy barrel liner cold sprayed onto a sacrificial mandrel, high strength steel core wire arc printed onto the liner, and a cold sprayed jacket with high heat capacity:

Actual manufacture of the advanced barrels appears to still be in its infancy. The ARDEC team identified their path forward to empirical analysis and testing, and noted the characteristics of the cold sprayed liner as being key to the effort. If the liner’s characteristics weren’t right, if it was too porous, too rough, or didn’t bond properly, the team would need to find another method and/or material to manufacture the liner.



Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • Giolli Joker

    I’m quite curious about the “cold spraying process”, I’m not familiar with it. Unless it is a generic definition opposed to thermal spray, and used to define kinetic processes, like HVOF, that, while still plenty hot, don’t rely on heat as a required feature.
    Would the assembly require a diffusion heat treatment to guarantee proper bonding? Hipping to minimize porosity?
    The definition of 3D printing here is catchy but far from properly descriptive of the processes involved. And if WAAM is indeed an additive manufacturing technique (I guess for relatively simple shapes), spraying hardly is… unless we want to start calling 3D printing any deposition of material by layers… like painting. 🙂

    Edit: I previously wrote addiCtive instead of additive…

    • roguetechie

      Cold spray is a very interesting additive manufacturing and even field repair technology which is just oozing with military potential, along with mining and other heavy industrial work done far afield!

      The Army Research Laboratory has a center for cold spray R&D as well as a bunch of really great PDF files dedicated to cold spray in their file repository.

      It’s a very good place to start if you want to do anything from just learn about the basics of the technology all the way down to getting into the nitty gritty ways and means of doing it for yourself.

      • Giolli Joker

        Yep, did some reading on it in the meantime.
        I was wrong to compare it to HVOF (which I’m familiar with) as this is actually cold and more focused.
        Still I’m bothered by the use of 3D printing definition.
        Here we have 2 additive manufacturing processes: basically spraying and cladding, neither of them is 3D printing.

        • roguetechie

          With cold spray they can and do build up parts, as well as rebuild damaged existing parts… That’s pretty 3d if you ask me…

          Also selective laser melting, electron beams, powder deposition, and even DLP resin printing does exactly the Same building a layer on another layer thing … As does FDM printing that uses ABS or PEEK etc!

          So I’m not sure where your objection is coming from, because you seem to be complaining that this exactly fits the definition of additive manufacturing / 3d printing!

          • Giolli Joker

            I’m complaining that additive manufacturing methods have “always” existed. Cladding like the WAAM is one of them.
            Even manual Tig welding to rebuild a geometry can be called additive manufacturing.

            Yet they are not 3D printing.
            3D printing allows you to create from the ground up a component.
            And it is called 3D printing because it happens in a confined space similar to a printer.
            A robotised spraying process at most would be a 3D spraying.
            3D printing is a broad category of additive manufacturing, but calling all additive manufacturing 3D printing is misleading.
            That’s it.

            Edit: to visualize a difference, these additive manufacturing methods require a substrate, 3D printing just a separate base from where to start building up.

          • roguetechie

            OK, that’s kind of where I thought you were going with this and I can kind of understand your sentiment.

            I kinda disagree, but at least I understand now and you’re making the distinction in a way which inherently makes sense.

            Where I disagree is in the idea that the presence or lack of a sacrificial or even structural substrate makes or breaks something’s designation as a 3d printer.

            Just as an example, on my 3d printer right now, when I print ABS plastic I put down kapton tape on the print deck which serves as a sacrificial substrate which also has the added bonus of making the print go better and be easier to remove than just printing onto my build platform.

            Now, when you bring up the enclosure thing though, I can see a stronger case in some respects… Just not when it comes to cold spray!

            Then again cold spray is kind of a bizarre hybrid between traditional welding and 3d printing. Depending on everything from your application, to use case, to budgets cold spray systems can be configured in multiple ways to fit what you’re doing. The reading I’ve done also indicates that it scales pretty gracefully compared to some other technologies, meaning that you can have everything from what looks like modified automotive paint booth equipment to a fairly small build volume enclosed delta printer that both do cold spray!

            The presentations on the Army Research Laboratory pages seem to mostly show larger scale applications and equipment, but my guess is that’s because they don’t want to give away everything they’ve spent time and money developing to EVERYONE with an internet connection!

            Not because they aren’t doing it other ways already.

            That’s just the impression I get though as someone who has been actively researching this particular technology for a few years now with the hope of being able to eventually get a really sweet cold spray based capability set of my own.

          • Giolli Joker

            Just to quote Wikipedia:
            “The term “3D printing” originally referred to a process that deposits a binder material onto a powder bed with inkjet printer
            heads layer by layer. More recently, the term is being used in popular
            vernacular to encompass a wider variety of additive manufacturing
            techniques. United States and global technical standards use the official term additive manufacturing
            for this broader sense. ISO/ASTM52900-15 defines seven categories of AM
            processes within its meaning: binder jetting, directed energy
            deposition, material extrusion, material jetting, powder bed fusion,
            sheet lamination and vat photopolymerization.”
            I believe that the level of readership on TFB is above average when it comes to technical terms and such, and Nathaniel F. is definitely the writer more suited to go into technical details. I’d like him not to cheapen his prose by the use of catchy and “vernacular” terms, rather to try to inform and elevate readers’ knowledge as he has proven several times he can do.
            By the way, note that the slides only mention “additive manufacturing”.

          • roguetechie

            Eh, I admittedly use the terms interchangeably. Mostly because if I say additive manufacturing people around here would probably think I cut drugs for ms-13 for a living LOL.

          • roguetechie

            The sad part is that people around here would be more horrified to know I build my own guns with exotic DIY tools than if I actually cut drugs for a living…

            That’s Portland for you

        • roguetechie

          Are you sure that you aren’t misunderstanding what the actual definition of 3d printing is?

          I’m not trying to be mean or confrontational, I’m just genuinely confused especially now that I’ve reread your comment and see that you seem to think that 3d printing and additive manufacturing are different things…

          Also, you might find this interesting.

          When I was originally doing research on cold spray technology and it’s origins I came across some Apocrypha which stated that cold spray technology actually has it’s origins in Russian welding technology which we got access to as partial payment for injections of dollars and things like grain shipments to the former Soviet Union during the fall of communism and chaotic breakup period.

          If this story is true, then once upon a time there were Russians doing similar stuff and just calling it welding LOL!

  • Garrett Hart

    I’d really like to see a more in depth follow up article to this

    • If I get more information, I’ll be sure to do so!

  • Brett baker

    I wonder if Youngstown State University will work on this. It is the home of America Makes, the new easier to remember name of the National Advanced Additive Manufacturing Institute.(Paid for largely by the DOD). If you have a future engineering student in your family, send them to YSU. Go Penguins!

  • SGT_B

    Well darn. I guess I can stop working on my patent now.

  • 10x25mm

    The surplus nitrogen and high temperatures produced by smokeless powder combustion nitrides the interior of small arms barrels, producing the ‘alligator hide’ deterioration of barrel throats as round counts increase. This ‘alligator hide’ is the result of nitriding and spalling of iron in the barrel steel.

    Cobalt also nitrides at high temperatures and pressures, producing several different stoichiometric ratios of cobalt nitride. At least one form of cobalt nitride (Co4N) is an adhesion agent used to promote bonding with copper in semiconductor interconnects when deposited by CVD. Deposition processes such as CVD and GDCS produce much more chemically active surfaces than the casting processes used to produce partial Stellite (cobalt alloy) chamber liners in the past. This is the basis of U.S. Patent 8,461,684.

    This suggests that severe copper fouling is likely to bedevil this barrel configuration. ARDEC might be better served to investigate metal aluminides as the liner layer in their barrel development.

    • Phillip Cooper

      ENGLISH!! DO YOU SPEAK IT?!!?!?

      (kidding, of course. This stuff is WAAAAAY over my head. I’m glad someone understands it…)

    • Paul Joly

      Nitrogen is a good component of the combustion for steel barrels, at high temperature, you can end up with a speudo nitridation. Hydrogen embrittlement is the main component, with the mecanical part, for barrel errosion.

      ADA440938

      • ostiariusalpha

        I think he meant galling instead of spalling also.

      • 10x25mm

        If nitrogen was beneficial and hydrogen detrimental, as suggested by the Australians, then you would not see the severe erosion when firing RDX containing (LOVA) propellants. RDX contains nitrogen and oxygen, but no hydrogen (or carbon). RDX containing propellants, used in high velocity tank guns, are universally acknowledged to be the most erosive with their erosivity increasing with increasing RDX content.

        This issue is too complex for a short post, but it is important to note that the tensile modulus of iron nitride is 17% lower than that of steel, while its shear modulus is 30% higher than steel (due to its different crystallographic structure). Thus a virgin steel barrel uniformly coated with iron nitride will retain its nitride coating until cracking develops because hoop tensile stresses determine performance. This can provide some reduction of erosion. But an uncoated steel barrel will spall nitrides created in fissures (on radial microcrack surfaces) by firing stresses, leading to spalling erosion, because shear stresses determine performance here. Crack tips progress by shear.

  • Raptor Fred

    Nice! Now time for 5000fps cartridges.

    • Major Tom

      More like we need 2 km/s (2000 meters/sec) velocity or more. Stay paper flat in trajectory out to 500 meters.

      • Quest

        5000fps is possible with usual propellant no problem, 2kms mostly isnt reachable.

        • Major Tom

          The M16 already achieves 1100 meters per second at the muzzle from conventional 5.56. Surely a saboted projectile with a good boost from a long barrel could do the rest of the way. The difference between 5000 feet per second and 2000 meters per second is only like 1400 FPS.

          • Quest

            As far as i know most gases have expansion velocity limits, you would need some really special propellant, which might get expensive/harder to manufacture/rare/ or has som other downsides.

          • PK

            The faster you push something, the harder it is to push it faster still. Additionally, as Quest pointed out, the maximum velocity of propellant comes into play. You can’t easily accelerate things faster than that, unless you want to play with the LGG concepts.

          • Curmudgeon

            Product of the public school system or just running your conversions backwards? That’s a 3,000 meter difference (drop the zeros, 5-2) which by my finely-honed estimation skills is about 9% more than 9 THOUSAND feet.

      • Raptor Fred
  • PK

    Importantly, this is toward the ongoing effort to make ultralight GPMGs without the need for a QD barrel. Really interesting line of thinking, streamline and simplify the load while making logistics that much easier.

    • Brett baker

      Do you seriously think there won’t be multiple reports of slagged together barrels and receivers a la WW1 if we don’t have QD barrels?

      • Paveway

        Do we envision fighting WW1 again where a MG will fire a million rounds in a week in a defensive position as routine operation?

        • Wow!

          So long as people exist and they have free will, you can’t rule any conflic as impossible. Strategies change to reside in the realm of unconventional, and so what was old may be new again. You don’t want to find that out when you depend on something.

  • Fast Forward

    Steel still appears to have some of the best characteristics regarding; conduction, convection, radiation and…….price.
    Typically, what wears out is the throat. I believe a liner, such as stellite, reduces the wear, but predominantly retains the benefits of steel. I thought that the newer M60 was a prime example of the use of this technology. Stellite is not easy to work with, but, has been around in the .50 cal for many years.
    3D printing obviously needs more time and more $$$$$.

    • FF

      Isnt stellite the stuff thats insanly expensive..? Cobalt might therefore be better.

      • Fast Forward

        I expect that the 3D printing will ultimately be; ‘insanely expensive,’ particularly if the R&D costs are also included.

        The main elements of Stellite are cobalt and chromium.
        Precision flowforming might be a better option.
        patents/US20100236122

        The open publication of this ARDEC Article/Paper probably indicates that this line of development has already been judged to be a; ‘dead end.’

        • Wow!

          People keep forgetting additive manufacturing is not a mass production technique. It’s whole development was for bridging the gap between engineers and manufacturers and enhancing capabilities for cheaper custom work in low quantities. Any time you try to apply 3D printing to a large scale it will be slow and expensive. Not a bad thing if you are making a part for a few hundred vehicles that will be obsolete in a few years, but an issue if you need to outfit thousands of small arms regularly.

      • Texas-Roll-Over

        Stellite is a cobalt chromium alloy!

        • FF

          Ok than it costs no bit more. Ah, what i meant was tantalum etc.

    • Renato H M de Oliveira

      Making big parts with high percentage of any metal/alloy other than steel or aluminum (and even some of these) will be prohibitively expensive for mass small arms production.
      What the NDIA presentation shows is that they’re starting to look at the general correct direction for lab scale production.
      It may take years to sort everything out and mass produce and field such barrels – and even then the solution may already be available, like the forced air cooling system of the Pecheneg.
      Also, there’s no way to predict if a totally different solution appears until there.

  • Phillip Cooper

    *header about Army*
    *Pic of Marines in Marine camo. Caption talks about Marines*

    Errrr…..

    • I believe that someday the services will be able to get over their divide and come together.

      • Brett baker

        “If pigs had wings,
        Away they’d fly;
        Way up to heaven oh so high,
        If pigs had wings,
        Away they’d soar,
        Up in through heaven’s golden door.”-Heywood Banks

  • Warren Ellis

    When I first saw the title I misread NDIA as INDIA. And then I wondered why the US Army was working with India on this.

  • jerry young

    If I am correct 3D printing is layer after layer of material bonded together by heat liken to Damascus steel which cannot hold up to the pressures of modern ammo, even with a liner that you would have to carry extras of to print new barrels are we at that stage in 3D printing that these barrels will hold up to thousands of rounds? another point instead of carrying extra barrels you would now have to carry printing equipment and supplies to make another barrel and wait for it to be made? sounds like the military should look into star treck replicators, I’ve shot machineguns where the barrels had to be changed due to heat and I’m not sure how a lighter barrel would hold up to the heat generated but I’ve been away from military weapons for many years now so maybe lightweight products are available that would hold up.

  • Raginzerker

    I wish I was smart enough to understand all this, sounds pretty interesting

  • bthomas

    Waste of time and money. Just use plain Jane MG-42 technology and swap out the barrels. Not hard. Works. Of course not fun for the R&D boys. Not fun for the corporations that want the contracts to produce new designs, etc. So what? IF there is a need for a longer wearing chamber, use what was used w/ good success in past eras … stellite. Problem solved. Everyone can go to figuring out how to develop and produce M-16 in something w/ a bit more pop …. say 6.5-6.8mm. Most useful on the ground. Fit rifles/carbines and GPMG’s to the round. Keep the .50BMG. Not much else to do.

    • Brett baker

      The problem is recoil. Anybody who can pass the physical(and some who can’t) can shoot 5.56 well with minimal training. The 6.5 and 6.8 have just enough recoil to take more effort to train initially, and more effort to keep trained up. People like to blame the 100 lb. Female com tech, but the 220 lb. Cannon cocker is just as bad. The extra time with 5.56 results in hits at longer ranges from the same shooter.

      • bthomas

        Recoil will be with us until Newton’s third law of motion is repealed. You can’t train people to not notice it. They will. It is cumulative. Answer is to process the little 100 lb. women out to civilian life and not take anyone in who is not at least minimally capable of handling the weapon(s) that are issued for use. I.e., don’t design around the smallest least effective weakest woman … but design for engagement against men who are of common size and then only accept recruits who are capable of handling those weapons. Otherwise, why not design the next shoulder fired anti-tank weapon to be something Barbie can handle w/o messing up her manicure?