Modern Intermediate Full Power Calibers 019: The Russian 6x49mm Unified

What happens when you take the two concepts of a traditional, full-power rifle and machine gun round, and a small-caliber, high-velocity round, and smash them together? You get one of the most extreme military small arms calibers ever developed, and one of the last small arms projects from the twilight of the Soviet Union.


The 6x49mm seems nuts until you see its competition: That’s the 10x54mmR heavy flechette round that was also designed for the Unified project, on the right. Note the groove in the body of the case on the 6mm – this was designed to help the steel case expand without failing, a critical design feature in a round as high pressure as this one. Image owned by Maxim Popenker, used with permission.


The 6x49mm Unified was not your average full-power military round. It’s a 6mm, or .243 caliber round – considerably smaller than almost every other round in its class. It fired a light bullet, just five grams (77gr), and had an incredibly high muzzle velocity of close to 1,150 m/s – that’s over 3,700 ft/s to the yanks reading this. These figures are much more characteristic of intermediate small-caliber, high-velocity rifle rounds, but the 6x49mm was no intermediate cartridge, as it produced muzzle energies of close to 3,200 J. Because of its high velocity, though, it was incredibly flat-shooting, and reportedly accurate to 1,500m. This claim seems extreme, but consider that the 6x49mm Unified boasts a supersonic range of 1,150m, a full 50% longer than normal .30 caliber full-power rounds!

Enough talk, on to the graphs:


In addition to its amazing external ballistics, the 6mm Unified was also far lighter than the round it was designed to replace, the venerable 7.62x54mmR. Compared to the 25.5 grams of the 7.62mm, the 6mm Unified weighed in at below 16 grams, nearly a 40% reduction in weight!

Ultimately, the fall of Communism and the dissolution of the Soviet Union ended development of the 6x49mm Unified round and the machine gun and marksman’s rifle that were designed to fire it. Also, because of its heavy propellant charge relative to its small 6mm bore, the round produced incredible barrel wear to go along with its incredible ballistics. In machine guns, the zippy 6mm wore out barrels after just 5,000-6,000 rounds, about a third of the life span that could be expected from a 7.62mm barrel.


The 6mm Unified (center) alongside the 5.45x39mm (top) and 7.62x54mmR (bottom), the latter of which it was designed to replace. Image owned by Maxim Popenker, used with permission.


However, there are rumors that the 6mm Unified is not yet dead, but merely sleeping. Will the Russians resurrect development of this ballistic wonder? Could improved barrel metallurgy finally make scorpion-pepper-hot rounds like this a reality? Who knows, but it’s fun to speculate!

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


  • Paul Epstein

    The use of high velocity smokeless rounds was enabled by barrel metallurgy. Now we find that our standard barrels are insufficient to cope with what is possible within modern ballistics, and I think it’s time to seriously look at the various solutions and demand to know whether they meet requirements.

    Even if the answer is ‘no’ on all fronts, maybe barrel life deserves it’s own examination. Barrels aren’t permanently attached anymore.

    • PK

      You’d be surprised and delighted with the most modern tech barrels. The problem is the cost, presently, as both the lining and “meat” of the high-wear-resistance barrels contain large amounts of less common elements.

      • Are there any materials examples you could give us for more research?

        • iksnilol


        • Guygasm


        • PK

          Current state of the art (late 2015, this was still current) for refractory metal lining is TaW alloy, that is, tantalum (89+%) and tungsten (10%) with the remainder trace elements, applied via bomb welding.

          The difference in durability is simply astounding, and it displays none of the bonding issues that Stellite 25 has shown since the 1940s. The problem is the enormous cost – I cannot stress how incredibly expensive tantalum is in the needed quantity.

          Imagine a single barrel for a rifle lined with this stuff, if it lasts 3-5 times longer in terms of useful life, it needs to cost 3-5 times as much as the more usual barrels… or what’s the point? Frankly, without a way to get a lot more tantalum, and comparatively inexpensively (space/asteroid mining, for example), these incredible barrels will be used only where absolutely needed, where replacement barrels are impractical to install in the field.

          • Giolli Joker

            I guess that Tantalum availability for military use gets sucked up by EFP warheads…

          • PK

            Correct you are. We use copper anywhere we possibly can for liners, but tantalum does get used for the more interesting designs.

          • Gunner4guy

            When you initially brought this up I was thinking primacord or detcord in the center to expand an unrifled liner ‘out’ to the outer barrel but the problem of manufacturing tolerance in the cord would seem to make that a problem….it’s been 40 some years since I had to study this(explosives/mining tech) as a required part of my degree in another area.
            One other thing that occurs is: a liner(rifled or not) inserted into an outer barrel which is then hammer-forged down onto the liner. Then, if unrifled use a spin-stabilized discarding sabot projectile.
            I’d rather have to 6mm round though at a lower velocity….sigh.

          • PK

            Not only does detcord not have a perfectly even distribution of explosive, or even predictable distribution when talking about this sort of application, there’s just not enough power… not even with 400 grain!

            Forging the meat of a barrel onto a liner would probably yield a mechanical interface like Stellite 25 lined M2 barrels (with all the problems associated with it) but I’m not 100% certain. By bomb welding the liner outward, the bond strength is simply astounding, and I’ve seen examples where the barrel is being sectioned/tested to destruction where the liner refuses to yield and is hanging freely where there USED to be barrel backing it.

            Something that strong, stuck that firmly, is the way to go for certain. If only tantalum wasn’t so rare and expensive!

          • George

            Ok… By bomb welding, I assume you mean explosive welding?..,

            I .. Am aware of a lot of odd explosive shapes but how does one line a barrel with something that way? Hollow liner tube around primacord line inside barrel?…?

          • PK

            I wish! It involves a purpose-developed LSC, a flyer tube, the liner material, and more mathematics than I care to think about! Basically, concentric rings as seen in cross section, although none of the layers are of entirely concentric thickness due to the nature of the needed applications.

            Outermost, base barrel.

            Next, small air gap.

            Next, liner to be welded.

            Next, air gap.

            Next, flyer tube.

            Next, sufficient quantity of a brisant enough explosive… which means there’s a lower bound in terms of size for a given velocity, a “critical diameter”, that is a solid wall until/unless more suitable explosives are developed.

            Originally, it was barrel, gap, liner, explosive. This requires a larger diameter and doesn’t weld as predictably, especially when you don’t factor in the shockwave building on itself, so to speak.

          • Giolli Joker


            Sealing the gap between liner and barrel at both ends and then having the explosion underwater (similar to explosive forming) would not work? Would the fluid waste precious heat?
            You’re making us curious about your workplace. 🙂

          • PK

            Water isn’t anywhere near solid enough to contain the operation to the needed size, the blank to be lined would have to be grossly oversized to resist extreme deformation… or it would end up with unacceptable internal tension! Even with the best methods, it’s amazing to see how far a section of barrel will spring open if you cut perpendicular through the wall, all the way to the bore.

            The usual process, by the way, is charging the blank barrel with the above device, putting this in a purpose-made (and very strong) form of the exact dimension of the barrel, closed on one end with an easily replaced cover which has a center vent, then of course the other side as well. It acts as a giant clamp to the outside, keeping things right where they should be. The flex is still quite something during welding.

          • Giolli Joker

            Cool! Thanks!

          • George

            You used ‘critical diameter’ oddly compared to the explosives engineering standard “minimum reliable detonation diameter”. Which depends on explosive and its tping (energy loss from sides of reaction zone etc)…

            However, the multi layer configuration with the flyer and then driven liner makes sense to me and the diameter minimums are implied, especially with the gaps required to get the flyer moving.

            (Now you’re going to make me find the Hugenots for Ta-W alloy tonight… See what you’ve done…).

            Out of curiosity, what is the flyer? Al?

          • PK

            Critical diameter being the minimum required diameter, given a desired liner thickness, flyer, and standoff distance. Under X bore for Y liner thickness out of Z material isn’t doable with current detonation velocities in predictable/repeatable explosives, so it doesn’t meet the minimum diameter requirement in that given situation. It isn’t about the minimum thickness or diameter to assure proper transmission of the shock front and an efficient explosion, as it is in more usual circumstances.

            The flyer is application specific and can be a wide variety of materials, depending on lining material, thickness, bore diameter, etc., and must be selected based on calculations regarding ideal bond strength.

            Happy reading, my suggested search terms are “explosive cladding”, “explosive welding”, and “explosive bonding”. Prepare for a whole lot of hits on these terms!

          • George

            Is the Ta-W10 applied thick enough to then rifle mechanically?

            Anyone tried doing this backwards, imploding a steel tube onto a Ta-W10 rod (or temporarily filled tube)?

            Anyone tried either explosively or pulse magnetically shrinking a larger diameter lined barrel to small arms diameters?

          • George

            Speaking of which, anyone tried net forming a sintered liner with powder metallurgy, then casting 4340 or 4150 around it?…

          • PK

            No idea on that one but I don’t see how trying to cast (did you mean forge?) onto a sintered substrate like that would give the sort of mechanical interface achieved currently, but this is still a fairly new area. I expect that if it’s been done, it’s been tried by various aerospace R&D teams since that’s where the majority of this technology originated.

          • PK

            In order: yes if you line it with that in mind, not to my knowledge but I see where you’re going with the idea, I seem to recall that being tried but the (even higher) internal tension caused enormous issues on a microscopic scale for barely any reduction in bore diameter.

        • Jerry

          You only need a barrel made of hot work tool steels. Those steels are only 30-40% more expensive than chrome moly barrel steel (some 10-20$ more in material for 30 inch .30 cal barrel).
          Those exotic materials like ceramics or super alloys are still far away from mainstream gun industry.

          • Are there any hot work tool steel alloys in particular that are suitable for barrels? Just a cursory google gave a slightly bewildering array of alloy options.

            I’d love to have a barrel for something like .22 Cheetah, 6mm Creedmore, etc that had a decent lifespan.

          • ostiariusalpha

            Stainless steels are best for a low round count (no semi-auto mag dumps) style of shooting, the throat and rifling last longer. There are proprietary stainless steels, like the Lothar Walther LW50 or Reardon steel that LaRue uses now, that are very durable and resistant to wear. These are a heck of a lot more affordable than Stellite 25 also.

          • Jerry

            H13 hot work tool steel is no brainer for barrel material. It is a very old and well known tool steel with more than adequate properties for high – temp and high – wear conditions of the inside of barrel. Hardened up to 50 HRC it has more ductility than 416R at 25 HRC (common SS steel for barrels) and toughness, strength and wear resistance is almost doubled. Using H13 grades from Carpenter (USA) or Bohler (Europe) you got all the necessary data regarding machining, heat treatment, cryo treatment and various surface treatments. Even a child could follow those instructions.
            Also the barrel made of H13 has one more great feature – dimensional stability (straightness and roundness of bore) up to 900F (480C) which is enough even for GP MG barrels.

          • Jerry

            H13 hot work tool steel…
            I wrote a longer reply on this subject a couple hours ago but post disappeared for some reason….

          • Thanks, off to do some googling 🙂

          • Jerry

            H13 hot work tool steel is no brainer for barrel material. It is a very old and well known tool steel with more than adequate properties for high – temp and high – wear conditions of the inside of barrel. Hardened up to 50 HRC it has more ductility than 416R at 25 HRC (common SS steel for barrels) and toughness, strength and wear resistance are almost doubled. Using H13 grades from Carpenter (USA) or Bohler (Europe) you will get all the necessary data regarding machining, heat treatment, cryo treatment and various surface treatments. Even a child could follow those instructions.
            Also the barrel made of H13 has one more great feature – dimensional stability (straightness and roundness of bore) up to 900F (480C) which is enough even for GP MG barrels.
            For some future mass production of high grade barrels there is a couple of methods in development with Cold spraying Titanium alloy barrel as most promising.

          • Awesome, that really sounds promising.

  • Tassiebush

    It’s a bad barrel life by military standards but not too bad considering the performance. In a switch barrel mg i might naively asume that it’d be possibly a trade off of extra barrel cost possibly being mitigated by reduced ammo cost assuming material cost matters in a national service round context, once the benefits of scale took hold (if they ever do/would)
    I was also amazed to see the drop chart not only because of the apparent advantage of this round but also in how closely the trajectory of the two current Russian rounds is. Sort of looks like you could use the same sight adjustments at the same ranges approximately anyhow.

    • Anonymoose

      Polygonal rifling could help with barrel life too.

    • Giolli Joker

      Good point on the charts.
      And in sniping context this round surely would do well.

    • Tritro29

      It’s called unified for a reason.

      • Tassiebush

        Yes it struck me that it had to be deliberate. I hadn’t been aware of it before. It’s a good idea though!

        • Tritro29

          You would never guess how the Unified cartridge got its biggest push…By noticing issues with the three tier ammunition in Afghanistan. Basically like the US found out in 2001/2.

          War. War never changes…

          • Tassiebush

            Haha re the fallout reference. Yeah I can totally see how helpful it would be to have the familiar characteristics between weapon systems. If someone can just learn all the same holdover points or adjustments then use whatever rifle or machinegun it would be far simpler. Optics could be interchangeable as well. A very wise choice especially when the armed forces have a large conscript component.

  • Ευστάθιος Παλαιολόγος

    Reading that 1,150 meters supersonic, how does this compare to, say, the .300 Win Magnum?

    And, will you expand your analyses to include sniper rounds such as the above, or .338 LM and .338 NM?

    • Giolli Joker

      Well… he went from Intermediate to Full Power, then we ask him to move to Magnum, then… please do the .50 BMG – yeah, 12.7×108 is much better – you, puny .50 I raise a 14.5×114 – pfui, 20×110 or GTFO…
      Let’s enjoy and see were this series will go.

      • Ευστάθιος Παλαιολόγος

        Just asking, not in a position to demand… 🙂

        • Anonymoose

          Go big or go home.

  • Giolli Joker

    This one is very interesting.
    And the potential for higher BC bullets is there.

    “10x54mmR heavy flechette round”
    Any data on this one?

    • Tritro29

      It’s one if the survivors of AO 27 program, although 27 was in 7,62×39.

      • Giolli Joker

        Tell us more. 🙂

        • Tritro29

          Study program about finding ways to improve stability of both firing platform and round as well as maintaining lethality over 300m. First idea was thrown about 1957/58, then full progam in early 60’s. Like with everything logical, the conclusion came down to the fact that to have those three points (a more stable platform, a more “stable” (flatter) trajectory, and enough lethality) a smaller round was needed.

          But unlike the US (No no) the guys were hell-bent on using a scaled down APCR “saboted” into an existing case type projectile. The rifle was more or less a basic Kalashnikov action first in 7.62×39 (Shireev 60-62) then tried with 7.62x54R about a couple of years later (with different group).

          • Giolli Joker

            Any idea on the ballistics?
            Do you know if the flechette pictured has been cut, or if it was designed that way?

          • Tritro29

            Nope it hasn’t been cut, that’s the Dvorianov 10x54R. It was designed so the sabots would cling on the flechette and the once exiting the barrel they would stabilise the rod by spinning in opposite directions. Interestingly the AO has been described as a scaled down copy of a 100mm tank gun. Dvorianov is also the man behind the modern 7.62x54R API/AP rounds.

            The x39 Shireev round went at 1000m/s. The Dvorianov at about 1.4Km/s. The new rounds were hitting consistently at 500m with iron sights, while the men struggles with the Ak past 300 and 400 with Mosin (allegedly).

            This program was happening more or less during the same era than the SPIW program…however while we started the flechette first (not really important) the US had a practical program started earlier…the .223 that finally would become the current rifleman’s calibre. While we would wait about 10 years later to introduce the round.

          • Giolli Joker

            So you’re saying that the barrel was rifled and it was imparting rotation to the tip of the flechette, while the tail was spinning in the opposite direction because of the aerodynamic drag on the fins?
            Cool. I was more familiar with APFSDS shot from smoothbores, first time that I see something similar.
            Thanks for the info.

          • Tritro29

            Yes basically it was a tank gun scaled down to fire needles.

          • Tritro29

            Also the APFSDS were first used with rifled guns…L7 from the British and also the first Soviet APFSDS rounds adapted to the D5T’s.

          • Giolli Joker

            Yep, I knew about British MBTs using rifled barrels, but I was unaware of “counter rotating” penetrators.
            Mostly because online it’s much easier to find detailed info on weapon systems used by American forces.

          • Tritro29

            Deep state, deep secrets ;-).

          • iksnilol


            I bet you issue it to your secret squirrel troops.

          • Tritro29

            What if I told you that a small company has applied to obtain a licence with strong resemblance to Tkb 454 and Tkb 517 right after the Soviet Union went down but wasn’t allowed to work on them?

          • Giolli Joker

            TKB022 FTW!

          • AHill

            I’d be in for a 517 like yesterday! Also, and this is just a thought; was the cut down part in the middle to promote fragmenting in the target? No doubt working with flechettes the ComSovs came up against the same lethality issue the US did?

          • Tritro29

            At that speed the logic was bending it more than disintegrating it. And yes not only lethality but also consistency in terminal ballistics. Small manufacturing errors would lead to erratic groups. Flechettes at that point required the same QC as a PK. SImply not interesting or economical.

          • iksnilol

            I would be mildly disappointed that nobody did anything with the TKB-022.

          • roguetechie

            Like me, you’re really hoping to get your paws on a tkb-022 one day right?

            To clarify, the one with a 16 inch barrel and an OAL still 6.5 inches from being non nfa right?

            I have drawings for the internals that make sense, and it’s certainly not an impossible design to manufacture fairly economically.

            What i would love to see is someone building them with a slightly altered setup involving a telescopic adjustable LOP butt plate, an 18-20 inch barrel, and a selection of pinned and welded muzzle devices.
            This gives you your ability to meet the 26.5 inch arbitrary minimum and should result in an eminently shootable weapon.

            I’d, of course, love to see one and two stamp NFA versions. Probably one with some sort of serviceable XM177 mini suppressor and the other with a bigger Finnish AK style reflex suppressor with slightly lengthened barrels.

          • iksnilol

            Yup. I’d go for a short barrel 10.5 inch with a 5.5 inch suppressor (Ase Utra, can’t remember the specific model. I tihnk it was the SL7).

            My idea would be to move the trigger and grip back 5-10 cm, and then add a buttplate that slides that much.

            I could live with bakelite, but if we are already in dream territory I’d go for some carbon fiber. Add a good red dot or 1-4 scope and you’d have something cool.

            that and of course one in 5.56 using AR mags with the regular length barrel.

            I also have the drawings 😉

          • roguetechie

            Personally I’d want a whole damn fleet from 5.45 16 inch bbl integrated suppressor with flash hider after the suppressor (1 tax stamp gun), a 6.8 wildcat necked to 5.56 with a pinned and welded serviceable without unpinning XM177 mini suppressor, and a longer action Grendel gun that meets 26.5 inches with pinned FH/QD reflex suppressor interface at 32 inch maximum with reflex suppressor mounted.

            I could see moving the grip back a few cm but not a bunch. Due to the originally fairly short LOP even without the grip moved back an extendible stock is probably warranted anyway for western users. Truth be told I mostly wanted it as an nfa dodge because I’m not a big dude as it is.

            Needless to say, barring a lottery win or some other multimillion dollar financial windfall I highly doubt I’d be able to afford an entire stable of tkb-022 in exotic configurations and calibers.

            One day I hope to have the skillset and equipment to make one or two for myself if nothing else, but for now I’ll limit myself to more pedestrian projects like attempting to clone a recent Iranian assault rifle design that has caught my fancy using mostly commercially available critical components.

          • iksnilol

            I never thought about how long the LOP is on the thing. I just know that I am tall so most guns by default are short, but I was thinking compatibility with short people.

          • roguetechie

            Being only 5 foot 7 or a bit more tends to make me see the world of guns and weight and weight distribution from a kinda uncommon perspective.

            For example I learned early on that I wasn’t going to keep a pistol from printing when carrying concealed. Once I learned that I became acutely aware that printing isn’t what makes you noticeable, it’s fidgeting fiddling and consciously trying to keep the damn thing hidden.

            In other words, I’ve learned it’s more about a quality holster you trust and wearing it so often that you’re aware of it but not consciously thinking about it. If you’re not thinking about it other people don’t notice it.

            With rifles I wound up with six position stocks on 20 Inch barrel rifles because I genuinely shoot best at about the third click. And I can short stock with very little trouble. It’s actually kinda nice, and I feel bad for people with gorilla arms.

            It’s actually what drives my semi obsessive love of the tkb-022. It would fit me nicely whereas a lot of guns don’t really work without me adapting to them.

            I shoot decently with a wide variety of platforms, but I can’t help but think that I’d shoot better with something that fit better.

            Long story short I thank God for six position stocks and former Warsaw pact weapons because they actually fit my frame.

          • iksnilol

            As a 1.9 meter freak of nature I find I never have the problem of gunstocks being too long. For short stocks I just scrunch up. There’s a limit to how much you can scrunch up though.

          • roguetechie

            I feel your pain, just sorta at the other end of the spectrum.

            There’s only so much I can stretch out to actively control a rifle.

            Because I love my 20 inch barrels, I had to go with the Canadian solution. Even today people still occasionally tell me of the horrors and broken parts and stove pipe jams I’m going to “constantly experience” because I have a 6 position stock on a rifle length upper.

            Guess how many I’ve had?

            Actually I can’t even tell you because it doesn’t even happen once a year. The configurations I use are actually almost freakishly gentle on parts thankfully.

          • iksnilol

            I don’t understand why a collapsing stock is going to induce malfunctions. I mean, the buffer is the same, right?

          • roguetechie

            Technically the A2 stock has a different buffer maybe, I think lol…

            Tbh when I saw the Canadians were doing it I just decided I was going to try it as well. I just ordered a damn lower and tested it, bonus is I don’t get so much spring noise.

            The guns cycle great with everything from cheaply steel case 55 grain to 77 grain. Honestly though at any given time my stocks are usually 2/3 62 grain steel case 1/3 62 grain brass case.

          • roguetechie

            Just remember brass then steel, you can make them kneel.

            Steel then brass you’re about to take it in the ass.

            It’s like the old drinking saying beer before liquor you’ve never been sicker. Liquor before beer you’re in the clear.

            Basically the steel builds up fouling in areas that it can handle just fine, but will make brass case work poorly.

          • Gunner4guy

            You’e lucky….I have to put up with a wife who can barely make 5′ when she stretches. The only way she can shoot some of my toys is off a bench or using a bipod or other rest. Still, she can pack a G19 GEN1 with an add-on adapter for a laser/light without printing.

          • roguetechie

            I can carry without printing, and when I do carry I make sure not to because I live in a left coast metropolitan area.

            What I was saying is that some people spend 3 hours getting dressed in the morning to match their glock to their shoes and not print, but then they are constantly ****ing with their piece and holster, doing exaggerated and obvious moves to keep people away from it, and generally moving like they have something hidden that they don’t want to drop!

            Basically, it’s the whole don’t act like you’re hiding something under your outside layer and people won’t think you’re hiding something or carrying a gun.

            You can still proactively move to avoid people getting right up on your holstered firearm without being blatant or obnoxious about it.

            It just goes to mindset and general safety of the carrier. It’s awesome to hear that your wife carries though! If enough females carry it will help keep even women who don’t carry a little safer.

          • Gunner4guy

            I can carry w/o printing also. I agree about the toying with the piece – popped a bunch cause I could see they had something in their waistband… and they could not figure out how or why I knew, didn’t tell them either.
            I KNOW where my weapon is, I don’t have to keep playing like you said. You’re in Condition Yellow pretty much all the time. People who don’t carry concealed off-duty don’t understand – to them you just stick/clip a holster on then fiddle with it, worrying, etc. Do it right the first time with a quality holster and it’s not necessary. You’re NOT supposed to be ‘comfortable’ wearing it, you’re supposed to be aware… part of the process.
            Late wife carried my Browning HP in a cross-draw w/o any problems so while body shape, etc. factors in, do it right and a full-size service wpn can be carried. Couple of my buddies came off active duty and went into the Secret Service back in the 80’s, both could pack Mini-Uzi’s under a suit coat PLUS their sidearms(shoulder holster) but unless you looked closely, you’d never know.
            I feel sorry for guys who wives who aren’t gun-friendly or at least neutral. Having two who packed/pack, I feel lucky as hell!

          • Sermon 7.62

            Yes! Do it again. Look at the mirror and spit.

    • Jerry

      Some scanned photo of this round and rifle system…

  • Anonymoose

    77gr at 3700 fps? That’s better than .223 WSSM ballistics! With hollowpoints instead of FMJs that could make one heck of a coyote-exploder…so much so that there probably wouldn’t be anything left but a cloud of fur and a smoldering crater. It would be like that goofy antigun cartoon where the guy says “I hunt with assault weapons” and is surrounded by blown-apart trophies.

    • Bob

      Haven’t seen that ad, but it sounds funny.

    • gunsandrockets

      It’s also better than the Hornaday Superperformance load for the .243 Winchester, which spits a 75 grain Vmax bullet at only 3,580 fps from a 24 inch barrel.

      Which really makes me wonder how such high performance is possible from the smaller cased Russian 6x49mm. Is the claimed performance true, or just hype?

      • I think the peak pressure was very, very high.

        • gunsandrockets

          What kind of powder?

      • Tritro29

        The round is a testbed anyway. It hasn’t been used long enough by enough people as to spot out the small or big issues with it. Also the ammunition was offered on the international market, then it was stopped very quickly 2 years or so. I don’t think that’s hype, I think it’s just a case of extreme perfomance obtained through zero or minimal compromise for long operation.

        This is indicative of the “why”, both the round and the SVK/TKB0145 designed to fire it became white elephants.

  • 11b

    Wow, 5k rounds out of a machine gun is NOT a lot. Like, at all. To put it in perspective, on a range zero/qual day my company alone would about 1k rounds through each SAW or M240 we had out there. The Russians would have been burning through barrels fast as hell.

    • Ευστάθιος Παλαιολόγος

      Every fresh can of ammo would be accompanied by a spare barrel… 🙂

      • PK

        Exactly the solution!

    • Jay

      The weapons that were supposed to fire this 6x49mm cartridge were in early prototype stage. Don’t imagine the Russians adopting a general purpose machine gun with that kind of barrel life.
      They would have come up with a solution. They ran into barrel life issues when developing the 5.45×39 cartridge and they fixed them.

      • “You get a stellote barrel! You get a stellite barrel! EVERYBODY HERE GETS STELLITE BARRELS!”

        • PK

          You’d run into serious problems shrink-fitting Stellite 25 liners into a bore that small. They’re not bonded or glued or welded, they’re mechanically fastened and retained by shoulders. They do fail, as .50bmg is already somewhat marginal in terms of being large enough to perform the lining.

          There are substantially more promising ideas currently in the works, but the cost is extreme. Frankly, it’s cheaper to design a fast and reliable QD mechanism and supply each gun with a larger number of lightweight, conventional, barrels.

          • Interesting. I did not know that, just that they did it with M60s. But then, I am no metallurgist!

            The tantalum alloys you talked about above sound interesting, and exorbitantly expensive.

          • PK

            “interesting, and exorbitantly expensive”

            Excellent phrase for the TaW liners, that’s just the problem. They’re difficult to apply which is quite an expense, the alloy itself is very costly, but once in place they tend to laugh off damage that would erode unlined, chromium lined, and even many Stellite 25 lined barrels.

            It’s still a fairly young technology, I expect that eventually there will be a solution used in nearly all centerfire barrels, or at least as an option as chrome lining is these days.

          • There was an experiment with full-length Stellite barrel liners for the Mk 46 Mod 0 from a decade ago.


          • PK

            You ought to see what was done after that… the very best, state-of-the-art, tantalum alloy lined M249 barrel. Frankly, I doubt it will ever wear out, but the cost is just too prohibitive to realistically think of manufacturing any large number.

            The thinking currently is that if this were the direction to go for LMG, SAW, GPMG, then QD would be done away with to lighten the overall system, as the barrel simply wouldn’t exceed accurate/reliable lifespan before the rest of the gun.

            Lining with chromium gives approximately a 64% increase in serviceable life, Inconel gives approximately a 500% increase, and then there’s TaW… approximately 3750%, and climbing. So far as I can find, the test M249 barrel still hasn’t worn out.

          • PK

            Exactly! And thanks to finally being properly funded as of last year, the TaW lining is coming along. Just need to get around the cost of the tantalum.

          • A quick change barrel system similar to the Steyr AUG would be ideal for a caliber like this.

  • Tritro29

    So after describing a dinosaur, Nath goes on to describe the comet that was supposed to erase it…but as we talk about the Soviet Union, In Soviet “Russia” the Dinosaurs extinct your comet.

    • Sermon 7.62

      You are a good Russian. Earned some likes from a bunch of Russophobes.

      • crackedlenses

        If I was as sensitive about the US as you are about Russia I wouldn’t be able to step out my front door.

        • Sermon 7.62

          Tritro can step out of his for sure. On four legs.

          • Tritro29

            … Ok. I love horses anyway. Or should it be bears?

          • crackedlenses

            Bears totally, especially if you like riding them shirtless….

          • Tritro29

            Bear riding without a pectoral attire is the sole privilege of the President of the Russian Federation. Plus think of the children.

          • crackedlenses

            Ah, yes, my mistake.

          • Zebra Dun

            Horses are nice!

        • Yeah, I don’t think Rousso’s doing a good job trolling.

          Here’s a clue, if you have to reply to every comment to keep the conversation going, you are not trolling correctly.

      • Tritro29

        I have zero insecurity issues. And I don’t take prisonners.

        • Sermon 7.62

          You have other issues.

          • Tritro29

            Tissues you mean? Here another one.

          • Sermon 7.62

            I see. More tissues, more issues.

          • crackedlenses

            We’re gonna need a truck from the looks of it….

          • yodamiles

            I sense butthurt in this comment section.

          • Zebra Dun


  • Ken

    Interesting case groove. You see it on Russian steel case .30/06 that’s imported.

  • Ben Loong

    I feel like this cartridge and the U.S. 6mm SAW were particularly tragic missed opportunities for LMG cartridges of the future. They might even have made for good DMR/sniper cartridges given their long-range performance.

    • I agree, and a part of me thinks this current 6.5mm mafia is really losing out by rejecting out of hand anything under 0.25″ caliber.

      • iksnilol

        Won’t bullets of higher BC be longer in 6mm than 6.5, and is the added velocity enough to compensate for that?

        • ostiariusalpha

          You can compensate, but barrel life goes to hell due to higher heat flux, which is a point that Nate tried to make about 6.5x55mm versus 7.62x51mm for machine guns back in the comments section of his January 31st article, “In Search of The Goldilocks Round: Intermediates From 1860-1943.”

        • I am gonna do an article on this soon.

          • George

            Swept volume does matter though, unless you just throw powder at it…

          • Swept volume matters, but the best compromises in my experience tend on the smaller side.

          • George

            I think that the spectrum of use cases now has to include suppressor suitability, and SBRs/short military carbines… and ginormous powder charge without enough swept volume makes suppressors much less effective. The more you expand behind the bullet in the bore the better. That argues for wide bores at a given chamber volume.

            For longer range, you comversely want sectional density and ballistic coeficient, and velocity. Those argue for (where I think you are going) the midcal long high BC bullet with a big push. Which needs a long barrel.

            I think another answer edges towards better sabots and something like .22 Accelerator rounds in an intermediate sized cartridge, but more 6-6.5mm than 5.5 for the subcaliber round, and perhaps bigger bore even than .308 (8mm? 8.5mm?), though balancing the swept volume and the sabot weight is an interesting exercise.

            Obviously, a subsonic solid projectile for suppressed use matters for this setup, as does sabot behaviour inside the suppressor (complicating to say the least..). But a base type sabot that does not open up wider may work…

            I’d start noodling around a .300 BLK but its case is too small, perhaps the 6.8mm necked up…

          • Figuring out how to make sabots that are both inexpensive and accurate would be a serious trick, and one that would unlock whole new ammunition configurations.

          • George

            Everyone goes straight to more complicated sabots for small arms. The earliest held the rear as projectile diameter converged a bit again. Cup type sabots, that just let the bullet pull free straight out the front due to differential air drag.

            You need some other mechanism in semiauto small arms to keep the projectile in place until firing, though. …

      • SlowJoeCrow

        I think barrel wear may be an issue. One of the selling points of the 6.5 mm target rounds like 6.5 Creedmore, 6.5×47 Lapua, and .260 Remington is significantly better barrel life than 6mm like .243 Winchester, 6mm BR, 6mm XC etc.

        • Right, but those rounds are much more overbore. Over the past couple of days, I’ve been exploring design space that would result in a round with no additional barrel wear vs. a 6.5mm round, and ballistically it’s pretty impressive (and much lighter).

          • Marc

            Like 6 mm HAGAR?

          • Somewhat close to that, although I am focusing more on the projectile than the cartridge case.

    • iksnilol

      HINT: It was called “unified” for a reason. They probably would’a made SVDs chambered for it.

      • Tritro29

        Or replace all the dismounted calibres with it…which was the ultimate goal once they had the first data compiled.

  • lowell houser

    “Also, because of its heavy propellant charge relative to its small 6mm
    bore, the round produced incredible barrel wear to go along with its
    incredible ballistics. In machine guns, the zippy 6mm wore out barrels
    after just 5,000-6,000 rounds, about a third of the life span that could
    be expected from a 7.62mm barrel.”

    Any prairie dog shooters out there? Something tells me you guys have an idea just what the barrel life on the DMR would have been. My guess is less than 1000 trigger pulls.

    • Hard to say. The easy comparison is with the .243 Winchester, but I don’t think they are directly comparable because the 6mm Unified uses a steel jacket, and because the DMR would have had a chrome-lined barrel.

  • I wonder if using say a 9mm sabot to fire the 6mm bullet would solve the barrel life problem?

    • TechnoTriticale

      re: that’s over 3,700 ft/s to the yanks reading this.

      Or about the same as the .308-based Remington .22 Accelerator (which, admittedly, was a 55gr .224 bullet in a .30 cal sabot). It may even still be in production. I haven’t paid much attention since it was introduced.

      I wonder if this series will touch on the sabot approach. It was obviously thought effective for certain tank rounds.

      • Marcus D.

        Part of the reason it is successful in tanks is that the barrels are no longer rifled, thus mostly eliminating the wear issue. Flight stability is accomplished with the fins on the projectile, rather than rotational force imparted during transit through the barrel as was the case in WWII. The electromagnetic accelerator guns operate in the same fashion, although I understand that the Russians are having issue with premature rail failure in their experimental models due to friction with the sabot.

        • gunsandrockets

          I can’t help but wonder if scale has a lot to do with how practical sabot ammunition is. It’s one thing to make depleted uranium anti-tank cannon ammunition. It’s quite another to make cheap ball ammo for small arms.

          The fin stabilized sabot SPIW ammo seemed a dead end.

      • As I understood it the accelerator rounds main problem was accuracy, due to the barrels being designed to fire much heavier .30 cal projectiles at lower speeds.

        I wonder if a custom barrel made with a twist rate optimized for sabots would solve the accuracy problem?

  • roguetechie

    I’m glad other people brought up the sabot angle. Though for barrel life and other reasons I still like my 5.56 minimum idea more.

    I think it could probably scale to give 6.5-8mm minimum gpmg and DMR round compatible with existing action lengths while having much better drop and energy retention characteristics than 7.62 NATO.

    That said probably nowhere near as crazy fast etc as 6×49 umg.

    • gunsandrockets

      How about this idea for improved ammo: 5.56mm to 5mm squeeze bore!

      (I presume you know what I mean when I talk about squeeze bore)

      The idea is an improved 5.56mm cartridge, that is lighter and higher performance while maximally compatible with pre-existing 5.56mm weapons and ammunition.

      The weapon would be something like an M16a4 with a replacement squeeze bore barrel of approximately 20 inches length. So the bore would gradually taper from 5.56mm at the throat to 5mm at the muzzle. Modern production technology should enable manufacture of a squeeze bore barrel almost as easy as a conventional barrel.

      The new 5.56mm cartridge (might also be steel cased to reduce weight?) would fire a 45 grain weight hollow base bullet with a conventional gilding metal jacket and a multiple component core. The bullet core would be a steel cylinder contained within the bullet jacket by two polymer donuts fore and aft, leaving some air gap in the bullet nose and between the sides of the jacket and steel core. The polymer donuts and air gap provide the bullet with the elasticity to squeeze down easily as it passes down the bore.

      The primary advantage this concept has over a 5.56mm firing saboted sub-caliber bullets is precision of fire (no discarding issues) and perhaps ammunition easier to manufacture within acceptable tolerances.

      • roguetechie

        Personally I favor the sabot idea specifically because the issue has been solved. There’s an existing sabot technology that actually works at even smaller scale quite reliably, and has been proven in multiple tests. Even better, it appears that the company behind the original solution is already seeking partnerships specifically to scale up to 5.56×45 and 7.62×51 versions.

        This company is cbj tech AB, the company behind the 6.5cbj and cbj-ms weapons system.

        What I was proposing is really just a simple extrapolation of the existing cbj tech sabot and the superb projectiles from 5.56×38 FABRL project. Housing all of this in a straight wall 30 carbine case loaded to at most 5.56×45 cartridge overall length minus the flexible internal element present in FABRL cases with modern propellants and a more case head supporting bolt than the M1 carbine has would allow you to get to 3250 fps MV out of the absolute minimum diameter case compatible with existing action lengths.

        Hence my calling it 5.56 minimum… Oh and it would weigh 50% or less than a loaded M193 round, maybe even 40%.

        Most squeeze bore small arms research has focused around the salvo squeeze bore concept. However, I could see experimentation around something like knight 6mm pdw round or better yet the 9 or 10mm colt MARS concept.

        Specifically, I’d be very much thinking along the lines of a 10-14.5 inch barreled gun with a screw on 4.5-6 inch little john adapter style setup.

        In theory you might be able to use both your low velocity full caliber and your high velocity squeeze bore with reduced performance in opposite configurations.

        • gunsandrockets
          • roguetechie

            Yes, that would be the one…

            The sabot they use has VERY LITTLE in common with something like the old accelerator sabots which you can still buy. They’re specifically designed to still be simple and manufacturable for cheap, while still giving much better results a la accuracy and dispersion for single and full auto fire respectively.

            Really if you’ve seen the results of them doing magazine dumps on large steel plates at 300 meters with an open bolt Uzi equivalent smg with a wire telescoping stock… It’s impressive.

          • roguetechie

            I took the basic technology of the cbj sabot and the FABRL projectiles and extrapolated what you can get out of a combined system from there.

            I have some other ideas twists and tweaks I’d like to try with the basic concept that should tighten up groups much more. Also the FABRL projectiles wouldn’t depend on tungsten, the need for tungsten IMO stems from trying to go too small with the overall package.

            Personally I’d like to see what could be accomplished in a pistol caliber SMG by using the cbj sabot and something like 38 casull or maybe just 7.62 tokarev.

            I’d also love to see what could be accomplished with a single projectile squeeze bore setup… It could very well be one way to balance the need for long pointed projectiles due to aerodynamic needs, and the need to fit the damn projectile case and powder in acceptable lengths and widths.

  • Kivaari

    What is the source for the claim the ring in the 6mm round was something other than a tactile and visual indicator that the round is a dummy?

    • That is a live round, although demilled I think.

      • Kivaari

        I’ve never seen such a case on live ammunition before. That is a really interesting way to avoid case head separation. Have you ever “halved” one of the cases?

        • I have never even seen a round of 6mm Unified in person before, let alone sectioned one.

          • Kivaari

            Perhaps someone can provide a spent .30-06 case using that system. It is something I have not seen before and would be interested in the theory-practice of the annular ring.

  • George

    Two bits –

    One, Cartridges of the World has a .444 base diameter (11mm I presume), does anyone have full case dimensions? Capacity?

    Two, keep in mind that 5000 rounds of ammo to blow out a barrel is probably 18 g x 5000 or 90 kg (plus links) and $1,500. The barrel is far cheaper and lighter than the ammo…

    • George,

      Great point about the barrel wear problem! Yes, it’s probably a more minor issue than it’s been made out to be. Probably more significant is the heat flux issue, as not only would barrels wear out faster, but in sustained fire they’d have to be changed more frequently.

      I do not know for sure what the dimensions are, but I have made a SolidWorks model based on an estimate assuming the same case taper and shoulder angle as 5.45x39mm, which appears to be roughly accurate based on images of the round. We do know that the case head is the same as 7.62×39.

      The case capacity of my SW model is 46.5 grains H2O, which implies that the 6x49mm Unified is running close to 70,000 PSI peak pressure!

  • JSmath

    Question – does the banding on the case serve primarily the same function as belting on other cartridges? Any extra advantages/disadvantages (reduced capacity/strength)?

    • No, it has nothing to do with headspace. It allows the case to expand without rupturing at the high peak pressures the round produces.

      • Robert Rodriguez

        I believe it is also a feature on Russian Autocannon ammunition, also for the same purpose.

  • gunsandrockets

    I take it then that the 6mm bullet was essentially a scaled up 5.45mm bullet, which accounts for its unusually light weight for its size.

    • Tritro29

      One could look at it that way. But clearly it’s a compromise between the whole spectrum of rounds used for dismounts (5.45/7.62M43/7.62R).

  • marine6680

    Great example of how everything is a trade off. Every increase in performance in one area, reduces performance in another.

    Modern steels and barrel making tech can reduce, but not eliminate the wear problem I would think. And that same tech could be used to further wear reduction on current platforms too.

    So even if you doubled barrel life with the new round, it would still pale next to current bullets used in similarly constructed barrels.

    But it may be worth it in the long run for a round with superior performance.

  • Sunshine_Shooter

    So, the Russians developed a 6mm version of the .22-250 and loaded it with 77gr bullets?

  • noob

    I really hope DefendTex will make a MetalStorm gun that shoots at stupid high velocity with the IP they bought from the defunct manufacturer of stacked barrel munitions.

    You don’t have to worry about barrel wear when you replace the barrel every reload.

  • Zebra Dun

    Too many gimmicks.
    That case is asking for trouble.
    The rd would do pretty much what the 5.45 x 39 would do and not any better except for it’s streak of lightning speed.