Future Firearms Ammunition Technology 006: Multiplex Projectile Ammunition – Two, Three, Four for the Price of One?

Multiplex rounds, left to right: .30-06 long neck duplex, .22-06 long neck duplex, .25 Winchester FA T115 short neck duplex, .25 Winchester FA T127 long neck duplex, Colt 7.62 salvo squeezebore triplex, 7.62mm M198 duplex ball, 9.53x76mm Winchester quadruple flechette, .330 Amron Aerojet triple flechette.

After World War II, US Army analysts determined that the effectiveness of the infantryman was not as closely related to their marksmanship discipline as had been previously thought. It seemed that instead, the random environmental circumstances and effects, plus the concealment and movement of the target, had much more of an influence on the probability of a hit than the ability of the shooter to fire his weapon with precision. With this knowledge in hand, arms designers in the West set out to improve the chances of the soldier to hit his target, and the most obvious solution was to simply send more lead downrange. The simplest way to do that was, of course, to create ammunition that fired more than one projectile per round.

Multiplex ammunition has, of course, been around for centuries in the form of shotguns and field artillery that fired multiple round lead balls out of smoothbore barrels, for much the same reason as post-WWII experimental multiplex ammunition. In this way, multiplex ammunition is really an old ammunition concept, not a “future” one at all. Still, the idea of modern standard infantry rifles firing more than one projectile per shot is one that bears considering as part of this series.

First, some terminology: “Multiplex” refers to the concept of firing more than one projectile per shot in general, while the terms “simplex”, “duplex”, “triplex”, quadruplex”, etc refer specifically to rounds firing one, two, three, or four projectiles at once, respectively. “Simplex” technically refers to most modern small arms ammunition, but it’s generally used only in the context of multiplex rounds to denote non-multiplex ammunition, or simplex loads for multiplex firing guns.

In the United States, the multiplex concept has been extensively investigated, and it potentially offers capabilities similar to hyperburst while still facilitating alternative full-power or intermediate-power loads with more range and energy than would be practical with a mechanical hyperburst mechanism. Multiplex ammunition can take the form of multiple high velocity flechettes, dart-firing “beehive” rounds for shotguns that increase their range, full-caliber stacked bore-riding projectiles, or stacked squeezebore projectiles that swage down to a smaller diameter (a concept that will be explored in the next installment). Multiplex rounds can also pack bullets with slightly different shapes, such as different ogives or canted bases, which give the weapon a randomized spread within one pull of the trigger.

Ultimately, multiplex ammunition is more expensive and usually heavier than corresponding ball ammunition of the same size. However, among the advanced concepts this series covers, multiplex rounds are uniquely within reach: The United States even successfully fielded a multiplex 7.62mm rifle round, designated M198, during Vietnam, which had the following characteristics:

Specification – MIL-C-60131 (cancelled in 1980)

Weapon – M14 Rifle and pending for the M60 Machine Gun as of July 1967

Bullets – a) Front bullet weighed 80 to 84 grains, made of B1112 free cutting steel with an electro deposited copper jacket b) Rear bullet weighed 81 to 85 grains, made of B1112 free cutting steel with an electo deposited copper jacket

Velocity – a) Front bullet velocity was 2750 fps + or – 30 fps as measured 78 feet from the muzzle b) Rear bullet velocity was 2200 fps as measured 78 feet from the muzzle.

Accuracy- Front bullet to impact within a 2 ” mean radius at 100 yards

Dispersion – Rear bullet impact was 5 ” to 10 ” CEP at 100 yards

Propellant – 45.5 grains of WC-740

Identification – Front bullet tip was painted Green No. 14110 per FED-STD-595

7.62mm M198 Duplex, far left, along with its single bullet counterpart, the XM256E1 Low Recoil round, and sectioned examples of each. Image from Ray Meketa's collection.

7.62mm M198 Duplex, far left, along with its single bullet counterpart, the XM256E1 Low Recoil round, and sectioned examples of each. Image from Ray Meketa’s collection.

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.


  • Mud

    Tubbs was messing around with this concept a few years ago and even had a product for sale. I think he marketed it more towards pig hunting.

    Overall, seems like a huge liability. In the example above, a 2 CEP projectile is ok, but it relies on a chunk of metal that is dead soft. The second projectile with a 10 CEP is ridiculous. 84 grains at 2750 fps and 84 grains at 2200 fps…….

  • Major Tom

    So why shouldn’t we just issue shotguns for everybody then? If you’re going to have the shot dispersion of buckshot at 100 yards with multiplex ammo, then why not?

    At least those don’t require fancy conversions or mechanisms to utilize different loads for different situations.

    • DIR911911 .

      you take your shotgun and I’ll grab my rifle we can both stand 150 yards from each other and see who gets hit first

  • Amplified Heat

    Third ball locked: MULTIBALL!!

  • John L.

    You can buy multiple projectile rounds from Lehigh Defense. Selection is a bit limited -.44 Special & Rem Mag, .45 Colt and 45-70.

  • Giolli Joker

    .330 Amron Aerojet triple flechette.
    It’s a pity the casing seems rather conventional, or this one would check all the boxes.

    • The case is aluminum, so it checks a lot of the boxes, hahah.

  • Daniel M. Ramos

    Hey, if tanks can use smooth bores and the total tech still allows them to make accurate shots at long ranges, then why can’t a similar thing be done in the world of small arms? It may sound strange but take a look at that new Uzkon UNG-12. That is a sweet weapon that pretty much has all of the features of a modern rifle except it has a smooth bore and is designed to fire 12 gauge shells. Couldn’t a shell be designed to fire a stabilized projectile that would allow for long range accurate fire while maintaining the flexibility of a smooth bore weapon to fire a large variety of ammunition suited to different scenarios such as 12 gauge high explosive rounds that can be set to air burst for example? Surely the technology is out there. Can you imagine how the gun grabber’s heads would explode if a semi auto smooth bore weapon could be made as effective and accurate at long range as a conventional rifle?

    • Kyle

      The same reasons that SABOTS and flechettes aren’t particularly effective for small arms. Expense and increased difficulty in manufacturing don’t give appreciable gains in lethality. Though is my memory serves the CAWS project did produce some really unique 12g rounds that extended the practical reach of the weapon out to 150 meters which was pretty impressive. I think the rounds were essentially razor blades with little folds on the back to stabilize the projectile.

      • Daniel M. Ramos

        That was back in the early ’80s. I just think that in 2016 we would be able to do better. Of course everybody will just pipe up that we are still using a design from the ’50s for our main rifle, so stick that in your pipe and smoke it. Ha!

        • Stan Darsh

          One would hope. Unfortunately, I don’t think shotshell producers see enough of a market, considering not a single one is willing to do something as seemingly straight forward as strengthening the polymer and brass enough to withstand longterm box-mag storage without form degradation.

    • DIR911911 .

      how would you know if the ung-12 is a good gun? reading about it here?

    • Giolli Joker

      12 Gauge has a very low operating pressure that would not allow the flechette to reach high velocity. The shell is even bulky compared to a 5.56 Nato.
      The main problem is that things don’t scale in real life as they do in our minds.
      Better technology helps, but some limits are embedded in physics.
      I would love a 12 GA APFSDS, the closest thing you can find is the Balle-fleche Sauvestre.
      Nice cat, BTW.

      • Daniel M. Ramos

        That is my giant attack cat Lucky. Sadly he is no longer with us. He was HUGE!

        Of course the current technology designed to fire 12 gauge shells has a low operating pressure I wasn’t proposing a solution so much as trying to illuminate an idea of an advanced technology smooth bore firearm that would operate in a fundamentally different way compared to the rifles we are so used to today. The idea is that similarly to the way smooth bore guns performed well for armored vehicles that there might be a way to make a leap in small arms going down a similar path. Things would have to be fundamentally different of course. Obviously no current small arms technology is designed to do so. The idea about using an independent adjustable liquid or gas propellant system is intriguing. There was a paint ball gun that actually used a propane combustion system as a propellant instead of compressed gas. I believe they discontinued it, but I don’t know why.

    • RocketScientist

      One of the main issues is scalability of tolerances. To achieve the accuracy you get from an APFSDS long-rod penetrator from a smoothbor tank gun, they have to maintain extremely tight tolerances of all the components. That is achieveable (at high cost) when building on the scale of a tank gun. Now if you scale the bore/projectile/sabot system down to a 12ga bore size or similar (thats about a 1/7 reduction in size, y my math), to achieve the same efficiencies, power, accuracy etc, you need equivalently tight tolerances (ie, tolerances 7 times tighter than needed with the 120mm tank cannon). That takes the difficulty of achieving them from “demanding” to “borderline impossible”. If you were comfortable paying dozens or hundreds of dollars for each round, with the bleeding edge of technology, you might be able to achieve that. Sacrificing on those tolerances for some measure of practicality results in what we’ve seen when these ideas have been tried in the past. Namely, SOME of the benefits, but with a singificant loss in accuracy, or range, or some other metric. You cant get something for nothing.

    • Kivaari

      12 (18.7mm) projectiles cannot carry enough explosive to be of value. Even 20mm has a small payload and it is one reason we have moved from 20mm to 25 and now 30mm. The increase in payload is dramatic.

      • Daniel M. Ramos

        What about the Frag-12 round that was created for the AA-12?

        • Kivaari

          Has it been adopted for anything other than a distraction device? My impression is it was a small “flashbang” device where it really just made a bang and some light. The thing isn’t a mini-grenade with anti-personnel effect.

        • Kivaari

          Speaking of the AA12. The gun seems like a solution to a problem that doesn’t exist. I’s swear I’ve seen demonstrations of that shotgun for at least 30 years. There really doesn’t seem to be a place where it would be better and as cost effective as a Mossberg M590 or Remington M870.

          • Daniel M. Ramos

            Really, I read that ground pounders that got their hands on them loved them. Being on the nasty end of an AA12 would certainly make me want to run in the opposite direction. ???

          • Kivaari

            Was there any real field use. I mean who wouldn’t have fun blasting exploding 12 ga rounds. But, do they have enough punch to make a difference in the real world. Would you give up a rifle for a shotgun unless you were only doing door knocking? A 40mm is serious and some think it doesn’t have enough punch.

          • Daniel M. Ramos

            Like every weapon system, its utility depends on the application. I’m sure in the close quarters of many urban environments it is very useful.

  • Bierstadt54

    “…the most obvious solution was to simply send more lead downrange. The simplest way to do that was, of course, to create ammunition that fired more than one projectile per round.”

    I think you and me have different definitions of “most obvious,” Nate. xD

  • FWIW: Here is a link to all of the US patents for multiple projectile cartridges (CCL/102/438). Mind you not all of these will involve stacked projectiles fired from a single barrel.


    Here’s a duplex design from none other than Georg Luger.


    • FYI: Here is a vintage write-up of the 7.62mm M198 cartridge from the October 1964 issue of Guns Magazine.


      This was followed a few issues later by a letter from a Canadian reader:

      Duplex Army Cartridge

      I found your article on the Army duplex cartridge in the October (1964)
      issue very interesting. I thought your readers might like to read the
      views of your “British cousins” on this cartridge. The following was
      published in The Rifleman, the British shooting magazine, which reprinted it from the Sunday Times.

      “The War Office at present doubts the need for the Duplex Cartridge…
      ‘the British Tommy has always been the most accurate rifleman in the
      world. The Americans aren’t so hot: they prob­ably need two bullets. We
      don’t… but we’re quite willing to listen politely.’

      “Just in case their attitude might be construed as sour grapes, the War
      Office hints that Britain long ago developed a far superior form of
      duplex cartridge.”

      This should rankle some Pentagon feathers!

  • Giolli Joker

    Uhm… more than 500 fps between the bullets.
    I’m curious about the internal ballistics: is there a pocket of gas that forms between the two projectiles allowing the front one to accelerate at a faster rate?

    • There’s some propellant between them, IIRC.

  • Isaac FluffyWolf Rader

    I think I remember hearing that there were accuracy issues. I’m not sure.

  • Giolli Joker

    Nathaniel, can please you open a new post: “all the weird experimental stuff I posted photos of and their supposed ballistics”?

    • JBM doesn’t like flechettes, so I couldn’t do most of them.

      • Giolli Joker

        Yeah, I can understand.
        I could also enjoy a simple comparison table with expected/experimental MVs and Energies. 😉
        Some background data where available.

  • gunsandrockets

    That 7.62mm M198 duplex cartridge looks like it would have been promising for some roles in the Vietnam War, say for an M60 in the LMG role.

  • gunsandrockets

    Let’s not forget the old buck-and-ball load for muskets. I’ve read a plausible claim that much of the carnage of the US Civil War during the early years was due to buck-and-ball loads fired at close range rather than Minié balls fired at long range.

    • Kivaari

      IIRC a book called “The Rifle Musket” (not rifled musket) did an analysis that pretty much showed the Minie’ bullets really didn’t do much beyond increasing the speed of loading.

  • gunsandrockets

    Some half-baked ideas took root in US Army after WWII. Project Salvo being one of them, a concept we still haven’t escaped the consequences of. Having lead to the dead ends of SPIW, ACR, and OICW.

  • Kevin Gross

    Nathaniel F, tried contacting you but no luck. Please try me at wolfganggross@hughes.net as I may have what you need. Kevin