M198: The Cartridge That Should Not Have Been

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.

Project SALVO’s experiments with multiple projectile ammunition did, surprisingly, result in the production of service ammunition. The 7.62mm M198 Duplex round was an attempt to improve the short-range combat effectiveness of the M14 rifle (so far as this author knows, it was never linked for use in the M60 machine gun – ED: Commenter Bud Harton mentions that it was linked for use in the M60, and this has been confirmed by other sources), but the fundamental limitations of duplex ammunition remained, and it was never successful. Eventually, the improved hit probability rifle would be realized in the .22 caliber AR-15, adopted as the M16 before the Vietnam War.

On the M198 round, cartridge collector Ray Meketa writes:

The lesson of Project SALVO was that nothing works quite as well as a conventional rifle, chambered for a conventional cartridge, firing one bullet at a time. But the lesson was not learned so quickly because following the SALVO II trials in December 1957, Operations Research Office (OCO) recommended the development of a standard length duplex cartridge based on the 7.62mm NATO case.

The cartridge showing the most promise was the T314, loaded with two copper-plated steel bullets in tandem. But, a U.S.Army Infantry Board report released in 1959 concluded that the T314 was not suitable for Army use and did not offer a substantial combat advantage over the standard Ball cartridge (7.62mm NATO M59). Unconvinced, the Army continued development of the cartridge through at least two more iterations culminating in the T314E3. In 1964 it was standardized as 7.62MM BALL-DUPLEX M198.

The M198 entered full scale production with the USMC receiving 4 million rounds for additional field testing. But, as the previous Infantry Board trials had concluded, the cartridge proved to be a disappointment. It did not improve single shot hit probability to the extent hoped for, which after all, was the goal of the duplex concept. There have been reports that some units in Viet Nam were equipped with M198 but, for the most part, production was halted and the entire program abandoned in the early 1970s. Reclassified as Obsolete (OBS), no cartridges remain in military stockpiles.

In retrospect, M198 seems most like an attempt to retrofit existing M14 rifles (a weapon designed around a theory of marksmanship that was becoming more and more glaringly obsolete as time went on) to match the theoretical benefits provided by smaller caliber weapons. While these benefits were eventually realized with the fielding of the M16, why didn’t the duplex ammunition succeed? A single 7.62mm duplex round was, after all, not much heavier than two 5.56mm rounds, while doubling the number of projectiles carried by the M14 rifleman.

Duplex ammunition experiences some major limitations that smaller caliber rounds do not. Being larger caliber rounds, the shooter experiences more recoil during firing. The two 84gr bullets suffer each from their combined recoil impulse as it affects the shooter’s accuracy and speed. In other words, while individual 5.56mm rounds do not throw off and fatigue the shooter as much as individual 7.62mm rounds, duplex 7.62mm rounds will. The ammunition load, too, is not improved. While the duplex shooter fires more projectiles than the single-bullet shooter, no more opportunities are afforded him than the latter, if their ammunition load is the same. In contrast, the small caliber high velocity rifle affords the shooter approximately double the number of opportunities to engage and destroy the enemy, for a given weight.

Finally, though the designers of the duplex rounds made an effort to ensure the twin bullets would follow different trajectories, and though this may have somewhat improved the hit probability of the rifle, the two bullets simply cannot separate very much over normal combat distances. As a result, the suppressive capability of the duplex rifle would have been much, much more similar to the single-bullet firing 7.62mm rifle than to the single-bullet firing 5.56mm rifle with its vastly improved combat load and recoil characteristics. The capability of riflemen with lightweight, small caliber rifles to affect more fire onto an area target more quickly, thereby overwhelming the enemy with superior fire output, is the greatest advantage the small caliber rifle brings to the modern infantryman. The duplex-firing large caliber rifle’s limited dispersion does not afford it as great an advantage in this respect.

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.


  • Esh325

    I think the Salvo idea they had back in the 50’s wasn’t a bad idea, it just seems they weren’t able to produce a rifle or cartridge that could do it. The AN-94 was really the only semi successful rifle that carried out the idea of having controllable bursts to improve hit probability in combat.

    • Lance

      the AN-94 was too expensive and complicated for regular use. Duplex rounds where expensive and hard for ammo makers to produce hence 5.56mm was better for rice paddy warfare we had in Vietnam. But id say if we went to war in Afghanistan instead of Vietnam in the 60s the 7.62mm would still remained the King of the Hill in performance in combat.

      • Esh325

        You hear lots of reasons why the AN-94 wasn’t adopted, we’ll probably never know why they actually passed over it. Some say it was too expensive and complicated like you said, some say it wasn’t reliable enough, some say politics kept it from being fully adopted. While the 7.62×51 is a better a round in some situations, I think the reason why the 5.56×45 was chosen for a main infantry rifle over the 7.62×51 was because the 5.56×45 was a better round in MOST situations encountered on the modern battlefield.

        • It was five times as expensive as the AK-74 and the Soviet Union was collapsing. No mystery there.

          • Esh325

            The Soviet Union was already dissolved by the time AN-94 was adopted. I think even with an improved Russian economy since that time, it still might be too expensive to produce even today. I’ve heard the AN-94 is used by Spetsnaz, but the vast majority of recent photos all show them using tricked out AK-74’s,AK-104’s, and AK-105’s.

          • SirOliverHumperdink

            Search TFB and you’ll see why.

    • What’s interesting is that the AN-94 “2-shot burst” feature was designed for the exact opposite reason as the SALVO. SALVO wanted to create a more shotgun like dispersal of rounds, while retaining the range of a rifle in order to increase the chance for making hits.

      The 2-round burst of the AN-94 was designed to be as fast as possible to limit the dispersion as much as possible, in order to allow both projectiles to strike the same place at 100 yards. The idea being that the first round would crack the ceramic plate, and that the second projectile will punch through the crack.

      I expect that in the next 10-20 years as armor becomes ubiquitous on the battlefield even for non-state actors (III uhmwpe armor is already $52 a plate from China now, and will only get cheeper to produce) we will see more in terms of the AN-94 and other 2 shot burst weapons.

      While the AN-94 may be 5x more expensive than the AK74, it would become cost effective if it allowed the use of conventional steel core projectiles to defeat plates, whereas the AK74 and similar would have to use very expensive Tungsten core projectiles for the same effect. Assuming a low price of $1 per round for Tungsten vs $0.1 for standard ball, the price of the AN-94 would become less than the AK74 within the first 1,000 rounds.

  • Vitsaus

    It was the cold war. The defense department had the money to spend on any wacky idea they wanted for the most part. The russians did more or less the same. Just look at the underwater assault rifles.

    • Dracon1201

      The difference is that they still use those rifles and they work.

  • CommonSense23

    I feel Project Salvo is one of those great missed opportunities in small arms development. They took the data from all the studies and went the wrong way with it(granted the technology at the time probably pushed them down this path). Instead of trying to increase the amount of projectiles fired, they should have went with increasing the amount of aimed shots fired.

    • Dracon1201

      So what they actually ended up with?

      • CommonSense23

        Not so much the 5.56 and M16/M4 but improved optics and realistic training. Doesn’t matter if you are firing 5.56 or 7.62 or even 30-06. Trying to use iron sights with the method of instruction that was taught for the longest time is extremely difficult when shooting at targets that are exposing as little as possible, are moving from cover to cover, only exposing themselves momentarily, and you are doing the same while shots are going around. Its hard to have good suppressive fire in those situations.

    • SirOliverHumperdink

      It is amazing how things come to be.

  • Bud Harton

    I was an armed helicopter crew chief/door gunner in Vietnam from Jan 1966 to September 1968. We started receiving linked M198 (four M198 and one tracer) ammo for our door guns (M60s) in late 1967. We were warned specifically tonot to use it in the outboard XM-134 miniguns.

    They made a nice pattern with about a three foot spread at or about 100 meters. we could tell that bu firing into water such as filled rice patties. Because most of us had jacked up the cyclic rate of fire of our door guns to probably well over 1,000 rounds per minute( we had no way to accurate gauge the actual rate) firing the M198s became problematic. As long as they were fired in the standard unmodified in the field m60s and limited to 6-8 round bursts, they were great. But in our guns, where we routinely fired single burst of 500 rounds duringa gun run, the M198 started “misbehaving”. The first thing that happend was the barrel heated way faster than they normally did which was actually pretty quickly. Then the flash suppressors started fragmenting and many were blown completely off the barrel and down range. The retaining on the threaded flash suppressors was always removed in order to remove and discard the bipods from the barrels (most of us had a stack of as many extra barrels as possible on the floor next to our seats). Because we just screwd the flasdh suppressor back on without re-insertoing the locking pin, it was always just a matter of time until the flash suppressor accompanied a fired round towards the targetr. Really neat went it was a tracer round and quite spectacular when a tracer rounmd removed the suppressor at night.

    • Wow, great comment, thank you! This is the first I’ve heard of linked M198.

    • John

      You’re a murderer.

      • NukeItFromOrbit

        And you’re an idiot, don’t trash veterans.

    • valorius

      You “jacked up” the firing rate of an XM-134 to 1000rpm? Or you jacked up the ROF of your M60’s to over 1000rpm?

      • iksnilol

        Presumably the M60s. Since he said that they modded the door guns, which from what I understand from his post weren’t XM134s

        • valorius

          XM134s could be used as door guns, and M60s could be used as forward firing reflex guns.

          So it could have been either, or.

          • iksnilol

            I know, but from the context I assumed the M60s were modded. He mentioned that they warned them to not use the ammo in the outboard XM134s (implying that in his case the miniguns weren’t door guns). He also mentioned regular unmodified M60s. If the M60s weren’t modded I doubt he would mention unmodded M60s.

          • valorius

            I’m particularly interested because i’ve never heard of this mod since I used to be an M60 gunner for some time in the US Army Infantry.

            The M60 was finicky enough as it was at 550rpm, cant imagine it functioning particularly well at double the designed rate of fire.

          • iksnilol

            Makes sense, though I am confused. Isn’t a low rate of fire advantageous?

            Or is it different for door gunners since you (presumably) don’t have to carry the ammo and whatnot?`

            Regarding the miniguns, isn’t the RPM on them adjustable due to them being electrically operated?

          • Bud Harton

            The M60Ds were used on “slicks” the troop transport version of the Huey (UH-1D and H). They were pedestal mounted. In the armed platoons, we used the standard m60. The linked ammo was one long link coming from either a minigun ammo box(1500 rounds and loaded backwards to the M60 feed) or sometimes just a wooden smoke grenade box. They were hung from the ceiling of the aircraft by a bungee cord. In the link is my buddy Jim Vxxxx and I firing from the aircraft and you can see our setup. Couple of things to notice, jim is firing his m60 upside down. That’s to keep the ejecting brass from going out of the aircraft and into the tail rotor.Crew chiefs always sat on the left as that was where the fuel por5t was, the smoke grenades are arranged on a homemade mount on the wall between us. This is an actually fire fight in 1967 or what my son calls “about 100 pounds ago”:

          • iksnilol

            That was certainly interesting, thanks for showing that.

            Must admit, it was weird seeing the M60 fired upside down but I can understand why it was necessary. + you had tracers so who needs sights anyway?

      • Bud Harton

        It was the M60s. We added a couple of nickels or nickel sized washers in the buffer slot in the butt stock and then added a half length of operating rod spring to the operating rod spring. You could still hear individual shots but just barely. Much later, I heard an MG42 for the first time since returning from VN and it was an instant flashback to the sound of a modded m60.

        • valorius

          What model M60s were they?

          • Would have been the plain-jane version.

          • valorius

            They used D’s for door guns too didn’t they?

          • Yes, you’re right. I was thinking versus E-series guns.

    • nova3930

      Great stuff. I love hearing actual experiences from guys that used this stuff.

    • J S

      Bud, thanks for the insight. Experience and info like you have is becoming lost to future generations. I spent time in the past doing weapons development. Unlike the others, I always appreciated the knowledge of how items were handled in the field, as opposed to us just making them “soldier proof”.
      As it goes, “When your ass is on the line….”

    • moecephus

      In 67 the gun ships supporting my project had the duplex rounds for use in the miniguns. It was green tipped. We opened a few to see what kind of bullets were loaded. We also had some miniguns firing 5.56 ammo as a test. Both the duplex rounds and the 5.56 weapons went away.

  • guest

    odd. I’d have thought duplex bullet ammunition would be more natural to apply to belt-fed weapons. It doubles the density of fire within the cone of fire.

    As for recoil, two 84 grain bullets weigh 168 grains in total. I can see this increasing bore wear, and I can see increased pressures and/or reduced velocities due to the second projectile eating up so much powder space within the cartridge case itself, but I am a bit surprised to hear it increased recoil measurably also.

    • Tassiebush

      I think the recoil point wasn’t that they recoil more. Just that you’re stuck dealing with the recoil of a 168grainer to send the 84 grainers on their way so there is no advantage in controllability or ease of shooting it well.
      Very good point about the cone of fire!

    • Looks like I was mistaken – it was linked.

  • WillLeach

    Awesome post. I know I’ve given you guys a hard time on some stuff, but I probably would have never seen this is not for this site. Its one thing to know that this kind of thing has been explored, probably too many times, but to think this got so far is kind of shocking.

  • mike

    The issues with projects such as SALVO is that there seems to be a lack of understanding of fluid dynamics – the behaviour of bodies that are in contact with each other travelling through a medium that is in state of dynamic flux (ie temperature, humidity, density). This is compounded initially by the impact of internal ballistics, thermodynamics and the resultant impact these have on external ballistics as the two bodies leave the barrel and begin to separate. It is unlikely that the solution to the behaviour of two bodies in contact with each other during separation will be able to produce the desired results on a consistant basis. Concepts, such as SALVO, although scientifically intersting, do not produce predictable consistent results outside a controlled environment.

    • MPWS

      Your scholarly tone is in right place. I agree with your view – there has to be comprehensive understanding of the issues first. Then, the major challenge is to control initiation of separation and its magnitude. When this is all done repeatedly, the solution can be on the way.

      I am personally long-term commitment to solution of this problem and have even name for it: Multiple Projectile Weapon System. I remain optimistic.

  • Here is a 1964 vintage article on the M198 Duplex.


  • Liam

    Interesting. In that American rifleman article on the equipment of MACV SOG that got posted here the other day, It mentioned one guy who used a cut down M14 loaded with duplex rounds. I guess they were useful in some cases.

  • Tassiebush

    Thank you for sharing your experiences. Very interesting and informative!

  • Tassiebush

    Anyone have an opinion of whether hand loading duplex is viable or involving special tricks or considerations?

    • Ho-boyee, I have no idea.

      • iksnilol

        Wouldn’t that legally be a MG? I mean it is firing more than one projectile per trigger pull.

        Also, I must admit, I am a bit interested in duplex ammo though I doubt it would play well with suppressors.

        • Tassiebush

          I’m pretty confident it’d be fine in most places legally. it’s nothing a shotgun doesn’t already do.

          • iksnilol

            I don’t know, those bolt actions sure are scary. I mean, what if somebody loaded up a Lee Enfield with duplex (or God forbid, triplex) rounds? Then they’d have 20-30 rounds in a 10 round magazine. Then the 308 guys would jump on the bandwagon with their G3s, FALs and M14s. And those things have 20-50 round magazines which could then be loaded with double or triple the amount of bullets.

            Then to top it off, somebody would load a 100 round double drum with triplex rounds, that’s 300 bullets in one magazine.

            Mass hysteria would be the only result I tell you.

            Yeah, it would essentially be a shotgun. Though it wouldn’t surprise me if people who don’t like firearms would cause some hysteria and try to get duplex rounds banned. “double the capacity for double the killing” or some such stupid tagline.

          • Tassiebush

            Haha you’ve discovered my evil plan! It’ll make my “murder” of running game easier! Yeah it’d upset such people if they were aware of the concept! Hysteria is certainly a good way to describe it!

          • iksnilol

            I am just saying, duplex and triplex rounds are a dangerous technology. Just imagine, instead of having to bother with making a 10 round mag for my Mauser I just load it with triplex rounds. Boom, I got 15 bullets then. 50% more than a Lee Enfield.

          • Tassiebush

            I’m terrified that there isn’t an international treaty against them! they clearly come close to rivalling nukes and poison gas in lethality but their potential for proliferation is massive! Somebody do something! I’m feeling emotionally fragile!

        • I believe the definition of MG in the US legal sense is “more than one round per trigger pull”. For example, shotguns are not considered machine guns.

      • Tassiebush

        Haha yeah neither do I! On the one hand I ponder whether it’s simply a case of matching the combined projectile weights to an existing load and all being well. On the other hand I can’t help but think there’d be some sort of barrel rupturing, hand pulping factor I haven’t anticipated… I’ve searched but only ever found handgun loads for them but the powders and pressures are more forgiving and the straight walled cases seem to make seating simple. Bottle necked rifle cases offer way more performance and uncertainty.

    • nobody

      People have loaded straight wall cartridges (such as .357 magnum, .44 magnum, and .45-70) with multiple bullets for a while, I remember hearing that someone somewhere on the internet was experimenting with a .357 load involving 2 wadcutters that were cut in half. You can also use round balls for a cheaper option if you don’t want to cast your own bullets.

      • Tassiebush

        Yeah I reckon those would be interesting and fairly safe. I’m extra interested and cautious about the concept in bottleneck cartridges. The performance sounds really good.

  • Bud, excellent response to an unfortunately low quality comment. Thank you for keeping it civil.

  • Geoff a well known Skeptic

    Back in the 70s there were .38 Special rounds loaded with 2 or 3 projectiles. The idea didn’t gain market share until the Taurus Judge and 3 buckshot loaded in a .410 shotgun shell in a .45 pistol. Geoff Who notes the intent of the Judge was carjacking defense.

  • Keyser Soze

    If you want to fire multiple projectiles at the same time, buy a shotgun.

  • Keyser Soze

    Wouldnt it make more sense to just fire a single projectile that was twice as long and broke up either in mid-flight or on impact?