Modern Intermediate Calibers 021: The US Army Marksmanship Unit’s .264 USA

We’ve discussed a lot of different rounds in this series so far, but today we’re going to discuss a round that actually has a shot of being adopted (at least in some form) by the United States military as a next-generation small arms ammunition configuration. That round is the .264 USA, developed over the past few years by the Army Marksmanship Unit (AMU).

The .264 USA is a direct response to combat in Afghanistan, where the primary threat to US infantrymen was emplaced 7.62x54mmR general purpose machine guns engaging Allied forces at long ranges, beyond where troops armed with 5.56mm carbines could effectively return fire. As a result, the .264 USA is a very large cartridge by intermediate caliber standards, measuring over 66mm (2.6″) long, and producing nearly 2,700 Joules of muzzle energy. Because of its size, much of the same analysis I wrote regarding the .280 British caliber of the late 1940s will be applicable to this caliber as well, something which we’ll get into more detail on later.

.264 USA Compared

The .264 USA (center) compared with the 5.56x45mm (bottom) and 7.62x51mm NATO (top). The .264 USA was designed to provide longer range than the 5.56mm, while reducing weight and size versus the 7.62mm.


Like larger 6.5mm rounds designed for long-range shooting competitions, like the .260 Remington, 6.5 Creedmoor, or 6.5x47mm Lapua, the .264 USA is designed to use long, low-drag projectiles, giving it ballistics comparable to or even superior than the larger and heavier 7.62mm NATO round. These excellent ballistics can be seen in the graphs below, alongside data sets for 7.62mm and 5.56mm. In addition to the 107gr and 123gr Sierra MatchKing bullets specified in the solicitation, I have also thrown in a 108gr (7g) lead-free EPR-type projectile with a finer shape and higher ballistic coefficient, to illustrate the maximum potential of the round.





From this perspective, then, the .264 USA is a knockout hit; with a higher ballistic coefficient than the 7.62mm NATO, and comparable velocity to the 5.56mm (in 107gr form), the .264 handily outmatches both in velocity and energy retention, flatness of trajectory, and resistance to wind. However, like the .280 British discussed previously, the .264 USA’s large size and considerable propellant load mean it produces much higher recoil than other intermediate calibers. Below is a chart comparing the recoil energies of different rounds from the same hypothetical 7 lb (3.175 kg) firing platform:


This shows that, in an apples-to-apples comparison, the .264 USA produces considerably greater recoil forces even than other powerful intermediate calibers like the 6.5 Grendel and 6.8 SPC. For additional perspective, the chart below shows the same calibers fired from different real-life host weapons, to give a sense of how these weapons would compare to each other:


We can see that from the 7.2 lb (3.265 kg) “AR-12” (not to be confused with the AR-12 rifle predecessor to the AR-18 developed by Armalite in the 1960s) developed by the AMU for the .264 USA, the .264 USA generates nearly as much recoil energy as the famously difficult-to-tame British L1A1 SLR FAL derivative! While it’s not shown on the graph, the .264 caliber AR-12 also produces higher calculated recoil velocities (the speed at which the recoil is applied, which helps inform whether a rifle will produce more of a “push” or a sharp “kick”) than the L1A1, as well.

Weight is another concern when adopting a round so much larger than current intermediate calibers. We can see how the .264 USA compares to those same rounds, with composite plastic/brass-cased, and plastic-cased telescoped .264 and 5.56mm rounds thrown in. The 107gr .264 USA CTA cartridge does nearly achieve the same light weight as the existing brass-cased 5.56mm round (at 13.6 grams, versus 12 for 5.56mm), but still falls well short of the 8.2 gram weight of 5.56mm CTA. It is also interesting to note that the .264 USA appears to have been designed from the outset for the composite metallic-polymer cartridge case configuration, and that rounds of this type were requested in the initial solicitation. Such cartridges have been produced, although the extent to which they will be or already have been tested, as well as the current status of that project, is unknown to me.


EDIT 9/25/2016: Anthony Williams has just published measured weight figures for the .264 and .277 USA rounds:

Some weights I measured today (from single samples of each):

264 USA with brass case and 108 grain bullet: 19.58 g

264 USA with polymer/steel case and 108 grain bullet: 15.03 g

264 USA with brass case and 123 grain bullet: 20.43 g

264 USA with polymer/steel case and 123 grain bullet: 15.87 g

277 USA with brass case and 135 grain bullet: 21.17 g

277 USA with polymer/steel case and 135 grain bullet: 16.69 g

I cannot help but notice that the figure for the 123gr .264 USA load is virtually identical to a weight estimate for an 8-gram 6.5mm GPC that I published in 2013:

With the case and projectile finished, and the specified performance achieved, all that was left was to weigh the cartridge and calculate its recoil. The volume of the brass case was 1.109 cm^3, resulting in a weight of 9.43 g. The weight of the powder charge was 2.35 g (36.3 grains), and the bullet, of course, was 8 grams. To calculate the weight of a large rifle primer, I set five together on my powder scale, weighed them, and averaged the result, which was approximately .35 g. When summed, the 6.5×50/8/00 weighed 20.13 grams; more than two grams heavier than Mr. Williams’ initial estimate, and nearly 70% heavier than 5.56mm.

For those interested in more discussion on weight and how it affects the load of the infantry platoon, I have written several articles on the subject, which you can read at the links below:

The Case Against a General-Purpose Cartridge

The General Purpose Cartridge Revisited

An Analysis of the Soldier’s Load with 6.5mm Cased Telescoped Ammunition (Part 1)

An Analysis of the Soldier’s Load with 6.5mm Cased Telescoped Ammunition (Part 2)

I should also point out that the 6.5mm cased telescoped (CTA) round in Kori Phillips’ presentation for the newly rebadged CTSAS (formerly LSAT) program may be based on the .264 USA, although the performance figures shown in the document may indicate an even more powerful round. Regardless, I have chosen to create my own estimate for weight for a CTA variant of the .264 USA, used in the weight comparison above.

One final dimension that is worth looking at is heat flux, or more simply, how quickly a given round heats up a weapon’s barrel. Rounds with a higher heat flux will heat barrels more quickly, and those with a lower heat flux will do so more slowly. With that in mind, I have compared the heat flux of the 5.56x45mm, 7.62x51mm, and .264 USA rounds in the graph below (efficiency figures were calculated using a Powley computer):


To sum up, then, the .264 USA represents a double-edged sword for the infantryman. Higher performance than either the 5.56mm or 7.62mm, it could potentially allow troops (especially those with support weapons like machine guns or marksman’s rifles) to reach out and eliminate the enemy at longer distances than is practical with the current squad-level small arms suite. However, its increased recoil, weight, and heat flux versus 5.56mm present a very serious question about what tradeoffs should be made in the next iteration of US and NATO standard small arms ammunition. Should these disadvantages – potentially reducing the rate of fire and accuracy of the infantry’s weapons – be accepted in trade for longer effective range and greater lethality? Or should another compromise be struck, instead?

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


  • George

    Question – has anyone looked at soldier tolerance to extended firing sessions integrated recoil per shot?

    I think recoil is overrated within normal bounds, as an ex-H&K 91 owner and someone who’s put hundred plus of 12 ga out in a session. Followup shot timing is more concern perhaps.

    But I’m big (6’5″).

    • I don’t think recoil is a problem for most in terms of pain, or even really fatigue (within the bounds of the rounds we’re talking about when fired from semiautomatic rifles), but it does seem to affect accuracy and ease of training. When NATO member nations switched from 7.62mm rifles to 5.56mm rifles, they universally saw a huge improvement in marksmanship scores virtually overnight. This improvement was so dramatic that in a couple of cases (Sweden, for example), the qualification standards actually had to be raised to compensate.

      So that would be my primary concern; losing that advantage would I think have a huge affect on the overall marksmanship quality of your fighting force. Given that there doesn’t seem to be any easy way to quantify this phenomenon, that begs for additional testing to create some kind of predictor for how beneficial or detrimental a round is in this respect.

      • joe

        But how do improved optics play into this? Who is expected to be looking for trouble and isn’t using an ACOG, and then who of the rest isn’t using an Aimpoint (or EOTech)?

        • I don’t know. Like I said, more study is required.

          • roguetechie


            Your charts in this article got me thinking about the 6.8 wildcat that can use 85-100 grain VLD 5.56 rounds. Since you’re much better at driving the ballistics and cartridge performance software suites than I am I have a few questions about that approach.

            1. I’m assuming that the 85-100 grain units pretty much preclude lead free in a 5.56 action length and probably in a longer vz52 intermediate action length, am I correct in thinking that?

            2. How bad would the heat flux be in either 5.56 or intermediate action length?

            3. How fast could we realistically push the bigger projectiles in the two action lengths while capping barrel length at 16-18 inches?

            4. What would the total cartridge weight look like?

            Finally, in general, is this an avenue that should be explored in your opinion?

          • ostiariusalpha

            I’m obviously not Nate, and he’ll probably contradict me ?, but here are my 2¢.

            1. If you were to shorten a 6.8 SPC case and its powder column with it, dropping the case volume down from 2.33cm³ to 1.95cm³, you would be able to maintain the 2.26″/57mm cartridge length that most contemporary intermediate rounds use; even with a long lead-free projectile.

            2. …You would also avoid a lot of the worse aspects of heat flux that would come from a full length 6.8 case; not that it would be all that awful on semi-auto or in a bolt gun, but it would be rough on the barrel if you want to maintain some kind of select-fire capabilities.

            3. This gets tricky. Wildcatters necking 6.8 SPC cases down for .224″ bullets have claimed velocities from a 24″ barrel of 3300 ft/sec for 75 gr, and 3000ft/sec for 90 gr bullets. Many who have actually tried these cats for themselves have found these promised velocities more than slightly exaggerated. And in a shorter barrel like you have proposed, a shorter, more efficient case could have better practicality, but you would be looking at realistic velocities more in the 2300-2400 ft/sec range even using more advanced propellants like SMP-843.

            4. A 6.8 case necked down to seat a 90gr Berger VLD would weigh approximately 15.2-16 grams (.536-.564 ounces), depending on the brass used. A shortened case with the same bullet might be more like 14.5-15.1 g (.511-.532 oz). A 5.56 Mk 262 weighs 12.9 g (.455 oz).

          • roguetechie

            Thanks you actually answered all of my questions quite well. Not only that but you caught how tentative I was about the reported velocities.

            Just goes to show you that there is no free lunch.

            However the more I learn the more that I see there are a whole smorgasbord of cheap nutritious and tasty lunches out there for those willing to put in the leg work.

            I’m not looking for perfect, just better. My ideal rounds now are ones that nicely fill the intended roles with a little juice to spare for growth potential, while being the same price or less, and where possible less resource intensive.

            The best round in the world does you no good if you can’t make 5 billion of them a year.

      • AK

        What about AK-107 type solution combined with this round? And I would believe that only the “tip of the spear” would be equipped with this new rifle/ammo combo, and even that could be saved for very specific missions.

        • Balanced actions don’t actually eliminate recoil, they just eliminate the elastic collision of the bolt group hitting the rear of the receiver. When you use them with larger calibers, they don’t work very well.

  • noamsaying

    The .264 has more recoil than 7.62 x 51. One of the reasons why the M-14 was not a big hit is that it was not real controllable on full auto. I saw an AR-10 video the other day, and that lighter weapon was clearly not real controllable after the first shot. One viable compromise might be to have dedicated grunts with .264s for long range shooting, with the rest of the platoon having a caliber more suited to the average engagement range. I think that is what is going on now to a degree with 7.62 x 51.

    • RocketScientist

      “The .264 has more recoil than 7.62 x 51.”

      Honest question, where are you getting this from? I’m not that familiar with the .264 USA (was aware of its existence and general description) so maybe you’re privy to info I’m not. But going off whats presented here, it has significantly less recoil than a 7.62×51 (in his charts, a 7.2 lb rifle firing .264 recoils significantly less than 7.62 fired from a 9.6 lb rifle).

      • noamsaying

        Did you read the article? The article said the the 264 had more recoil.

        • Recoil velocity measures how fast the gun is moving, not its magnitude. So a 7.2lb .264 USA round would kick more sharply, but with a somewhat reduced magnitude than an L1A1.

        • RocketScientist

          Yes I did. Unlike you, I have a modicum of reading compehesion however. Here’s every time they use the wrod recoil in the article:

          “the .264 USA’s large size and considerable propellant load mean it produces much higher recoil than other intermediate calibers.”

          -INTERMEDIATE calibers (ie 5.56×45, 6.8 spc, 6.5 grendel, 7.62×39, 5.45×39, etc… NOT 7.62×51 as you assert)

          “This shows that, in an apples-to-apples comparison, the .264 USA produces considerably greater recoil forces even than other powerful intermediate calibers like the 6.5 Grendel and 6.8 SPC.”

          -Again, INTERMEDIATE calibers (they even call out a few specifically this time), NOT a full-power battle rifle cartrdige like the 7.62×51 as you assert

          “We can see that from the 7.2 lb (3.265 kg) “AR-12” (…) developed by the AMU for the .264 USA, the .264 USA generates nearly as much recoil energy as the famously difficult-to-tame British L1A1 SLR FAL derivative! ”

          -NEARLY as much recoil (which by definition means less than) as a 7.62×51 rifle that weighs literally 30% more!

          “However, its increased recoil, weight, and heat flux versus 5.56mm”

          -Again, compared to 5.56, NOT 7.62×51.

          Then of course there are the two charts that clearly show .264 USA having consdierably lower recoil than 7.62×51, whether fired from the same theoretical rifle (17 ft-lbf vs 10.5-11.5 ft-lbf) or when fired from two different-weight actual rifles chambered in their respective rounds (15 ft-lbf vs 10.5 ft-lbf).

          Maybe I am completely missing something, and if so I’d be happy to learn what, but I just don’t see how this article (or any other information I’ve seen, or even common sense) supports the claim that the .264 USA recoils MORE (or even as much as) a 7.62×51.

          • lostintranslation

            noamsaying…….There was a YouTube video, some years ago, showing some shooters, I believe from the AMU, using a 6.5×47 calibre AI-AW. The recoil from 6.5×47 appeared to be very light and the comments during the video, from what I recall, were highly complementary.
            The video, however, disappeared.
            After some; ‘searching,’ and email communication, it appears that the video was removed as a result of a ‘copyright violation.’ It’s a shame the video is no longer available as I believe it would have positively added to the discussion.

            On another aspect, the AR-15/M16/M4 carbine sustainable rate of fire was, I believe, 12 rounds per minute. I believe that this has risen to 17 rounds per minute with a newer heavier barrel. With this in mind a full auto capability is something that, for many reasons, needs to be used judiciously.
            The concept of ‘Heat Flux’ is an interesting way to describe the reality.

            In CQB the option of occasional ‘full auto’ sounds reasonable.

            For combat, in wide open spaces, the need for ‘full auto’ from a rifle, should, perhaps, be questioned.

  • Mike N.

    Without a drawing and just from eyeballing it, it looks like a 6.5×45 Lapua but with a shallower shoulder angle.

  • AtomicYeti

    Very interesting article(s). Although i think it is hopelessly impossible to introduce an intermediate round today, as proliferation of existing ones will keep armies tied up for a long time, until necessity dictates otherwise.

    • Current thinking seems to be on the side of a paradigm shift happening soon, in the form of lightweight cases.

      At that time, one or more new calibers will likely be adopted.

      • Jay

        Absolutely agree with that, and I think the army should do some serious testing and experimenting to find the best solution going forward.
        I think it would be a huge wasted opportunity, to move forward, with new cartridge architecture and not optimize the cartridge, or cartridges better.

      • AtomicYeti

        As long as the pros out weight the cons substantially, otherwise it will be a logistical and economic nightmare. After all, rifles don’t win battles, they are just offensive modules, the question is whether there is reason enough to undergo such a change, which will at some point require a new platform, rendering millions of rifles useless. Unless they want to mold the new cartridge in such a fashion that will allow its use through existing platforms. I’m not questioning what merit a new cartridge will yield, just whether it is feasible.
        The dual cartridge 5.56/7.61 works as intended without additional costs as things are today. NEW “multical” rifles allow the use of different calibers depending on locality. I’m not against experimentation, maybe lightweight cases is a good start, but it will take time or a serious necessity whether real or artificial, to get the cogs going.

      • Seamus Bradley

        Lets not forget one of the big reasons for the EPR round having the penetration it has… Russian and Chinese steel body armor. Uncle Sam is always worried about a fight with the Big Boys. Any changes they make has to play to that scenario. Thus a single caliber in a lightweight polymer/telescoping case will reduce the logistic burden. The .264 (6.5mm) has a higher BC and thus combined with the EPR design better penetration, “possibly” getting close to defeating a Level IV plate and absolutely destroying a Level III well beyond 100 yards (as seen with the M855A1 EPR).

        One thing I know for sure, right or wrong; Logistics, Budgets and Russian/Chinese military developments will dictate this decision, NOT ballistic charts.

  • jrt 82

    I was surprised that the 270 Winchester was not on the list of comparisons.

    • .270 is really a full-power round, not an intermediate one.

  • iksnilol

    “intermediate” cartridges like this one are a better replacement for 7.62×51 than 5.56 in my honest opinion.

    • ostiariusalpha

      A better, lighter GPMG round sure would be helpful.

      • iksnilol

        Having performance superior to 7.62×51 at slightly more weight than 5.56 sounds amazing to me to be honest.

        • ostiariusalpha

          .308 Win/7.62x51mm needs to go the way of .30-06, and be repurposed as strictly a hunting cartridge. Which it does just fine at.

          • iksnilol

            Aw yiss.

            Hate myself for it though, but it looks like my first very own (mine only) rifle will be a 30-06 Mauser simply because I can get ridicilous amounts of free 30-06 brass for free.

          • .30-06 is probably my favorite hunting round. It can do virtually anything very well.

          • iksnilol

            I know, but I’ll feel like a fudd. + the action is long, like “rebarrel to 9.3×62 and shoot elephants” long.

            But hey, free high quality brass. Can’t argue with that. Could possibly cut down the brass down to .45 acp when the neck gets worn out. So I’ll eventually go full fudd with my legal firearms ownership here in Norway.

            It’s a mildly unsettling development.

          • Kivaari

            You can’t go wrong. The ’06 will do anything a person could ask, except be something it isn’t. It wont ever be a .22-250 or a .375 H&H but it sure can do just about everything else. It has a great advantage if you like shooting heavy bullets in the 190-220 gr. weight. With heavy Sierra MatchKing bullets it is a great long range target round.

  • Rob

    The Services should issue a variety of firearms at the squad level. Depending on the mission environment outfit the squad with a mixture of AR-10’s and M4’s. No single rifle can do it all. Don’t try to force it. The above cartridge is interesting and might fit into the mix, but it can’t do it all, either.

    • Seamus Bradley

      Training, budgets and supply would be a nightmare. You would literally need to have to qualify on a half dozen different types of rifles every year instead of just 1. Add in logistics of ammo, magazine, pouches, plus changing over optics, laser, lights all add up.
      I agree no single rifle can “do it all” but no single unit can either. That is why the vast majority of the US military focuses on the 90% solution for 90% of the problems and has a handful of different units that each specially in different tasks (airborne, seaborne, direct action, reconnaissance, etc) that have the tools they need for the special jobs they do.
      Please understand that 155mm howitzer beats any rifle bullet any day. The US Army thinks big and I mean REALLY big. Lets not forget this is the same Army that though nukes out of a Howitzer (Atomic Annie) was a “good idea.” Anything that reduces the logos burden to Uncle Sam is seen as a HUGE plus. I doubt this round will get adopted but eventually something like this will, when the Army has the budget to make it happen and the US Air Force isn’t wasting all our tax dollars on crappy F-35s.

  • Jay

    I think the idea behind this cartridge, just like the 6.5CTA cartridge Kori Phillips showed in that slide, is to reduce the weight of the general purpose machine gun and designated marksman rifle, not to create a proper intermediate cartridge, to replace both the 7.62 and 5.556mm cartridges.
    This cartridge is designed by a sniper unit and that should tell you a thing or two about their intentions. The 6.5mmCTA is simply the 7.62mm CTA case, loaded with a 6.5mm bullet, so that’s as much intermediate cartridge as 6.5mm Creedmore is.

    Anyway, Thank you for the article. The cartridge does have really good ballistics, so it would be fun civilian round.

    • Smedley54

      Pretty much anything 6.5mm will shoot well, but with high volume shooting the recoil catches up to you. Some serious, competition shooters are flirting with the 6×47 Lapua – a necked down 6.5×47 Lapua – because recoil wears them down during long matches. The smaller bullet does give up some targets at long range, so there’s the retained energy vs. recoil trade-off again.

    • Seamus Bradley

      While the design may be intended for a “sniper” round buy the world class shooters at the AMU, nothing says the Army will load Sierra Matchings in it. Odds are the average grunt will get an EPR round and there will be some special units that get better bullets.
      We already have 5.56 tracer, 5.56 AP, plus phasing out M855 “green tip”, and the new EPR M855A1 round in common service. No reason why we couldn’t have an EPR .264 for the grunts and a super duper “sniper”/BTHP .264 for the dudes with beards and specialty units.

  • Blake Allen

    One round can’t do everything. People need to stop thinking like that. We need one round for the basic infantry troops and one round for the designated marksman. Perhaps the 5.56 could be replaced by the 6.8 as the infantry caliber and the DMR could be changed from 7.62 NATO to .264 USA

    • Vitor Roma

      6.5 is better than 7.62 at everything: range, accuracy, less recoil, less weight, more energy. Now from 5.56 to 6.8 it wouldnt be worthy. 6.8 has a rather mediocre BC and M855A1 seems to be more than capable enough in the 500 meters range.

    • mechamaster

      Maybe the 6,5x40mm wildcat ( pict taken from the old TFB article ) utilized 6,8 SPC with 6,5 Grendel projectile will fit the role for CQB up to 600-meter engangement range.
      Plus, by swapping the barrel, it can utilize the 6,8x43mm SPC too.

      • Again, the 6.5x40mm isn’t different enough from the .264.

        • Blake Allen

          What about the .25-45 Sharps?

          • Worse than 5.56mm in many ways.

            Another thing to remember is that none of these conventional cased rounds stand a chance of being adopted; whatever any new rounds look like ballistically, they will be designed with a new case configuration.

    • No point in doing that; the weight penalty for .264 USA and 6.8 SPC is virtually identical. The .264 USA just has somewhat higher recoil energy.

      Ideally, 5.56mm would be replaced by something with similar performance, but lighter.

      • iksnilol

        So basically something that is to 5.56 what .264 USA is to 7.62×51?

  • Ben Loong

    I wasn’t even aware this cartridge existed before.

    The downsides in weight and recoil make me wish they had taken a second look at the 6mm SAW and made something closer to that.

  • LazyReader

    Good enough for competition, good enough for terrorist brains

  • Disarmed in CA

    Doesn’t look like it’ll fit in an AR-15, Would AR-10 ?

    • ostiariusalpha

      Yes, these “super intermediates” usually get fired from short-action guns, like a .308 frame AR.

    • It could fit in an AR-10, but it’s designed for an AR intermediate in size to both.

  • demophilus

    Might be nice to see how 6.5 Creedmore or Norma fit in these charts, graphs, etc. In theory you can swap them into legacy 7.62 NATO systems, unlike this, which doesn’t seem to fit into either that or 5.56.

    • Honestly those 6.5mms aren’t good fits for military weapons, primarily because of barrel wear issues.

      If you wanted a drop-in replacement, something like 7mm-08 would be better.

      • demophilus

        If you say so. But if barrel wear is your issue, you maybe want to look at DTIC presentations on barrel liners — ceramics, SiN, etc. Research has given us ways of mitigating barrel wear that weren’t available in the 20C.

  • iksnilol

    I doubt it is milsurp/armyplus. It doesn’t have any nato/military marks. It’s just marked “Norma” and the the caliber.

    It’s target and hunting ammo, and plenty of folks don’t reload so they just throw their brass in a common barrel thingamajig we got on the range.

    I’d like 6.5 but I don’t got free brass in ungodly amounts in that cartridge. Remember, I’m a somewhat poor college student.

    • gusto

      I am not an avid handloader

      but I wouldn’t touch brass from a thingamajig

      you have no idea how many times it has been fired/reloaded

      • iksnilol

        Eh, if it isn’t corroded nor deformed it should be fine.

        • ostiariusalpha

          Yep, just be sure to check the interior webbing around the case head with a probe for any developing trenches. Then anneal the brass of the neck and shoulder, and you’re good-to-go!

    • Smedley54

      Free Norma brass?! Heck yeah! How about a .26 Nosler just for fun?

      • iksnilol

        I dunno, I doubt I can afford barrels that often 😛

        But I guess that’s one of the appeals of the .30-06 action length. You can shoot plenty of different stuff outta it. How easy is it to make a switch barrel out of a Mauser 98k?

        • Smedley54

          Repeat after me, “Barrels are consumables, barrels are consumables…” And remember all that free brass. How about a nice 6.5×55 then?

          • iksnilol

            Gasoline is a consumable, doesn’t mean that I redline my engine 😛

            Was thinking about that. Can build a switch barrel, go with 30-06 for… economical shooting (ironically enough) and 6.5 for flavor and range. Just wish there were some detachable 5 shot mags available for long action Mausers 🙁

            Researched the swich barrel thingamajig, isn’t actually expensive, can get it done for like 200 bucks (the switch barrel add-on and the hands to add it + adapt 2 barrels for it).

  • Monty01

    Nathaniel, This is an excellent piece of analysis. Congratulations and thank you for taking the time to do it. I hope that anyone responsible for next generation small arms will read and take note of your comments. My own belief is that NATO needs to move beyond 5.56 x 45 mm in all its forms. The number of different loadings and the incompatibility between different nations’ weapons and ammunition destroys any notion of standardisation. I have no doubt that the .264 USA is an excellent cartridge – and if it became the next NATO standard I wouldn’t complain – but it reintroduces considerable felt recoil and I believe that the task of training soldiers to shoot accurately, especially when under stress, would become more challenging. There is also the increased weight penalty with a standard brass case round, which would certainly be required. Elsewhere, it has been noted that the one factor limiting further development of 5.56 mm NATO is its 45 mm case length. If this could be increased, you would improved performance. Of course, if you change the cartridge length, you’ll need new weapons to fire it, so you might as well go the whole 9 yards and increase the bore slightly too. This is the point. You don’t need to up the performance of 5.56 mm NATO by very much to have a highly effective round that matches 7.62 mm at least to 600 metres, but that remains true to the SCHV concept. In many ways this is what the US 6 mm SAW cartridge was. Ideal for machine gun use, it would have been at least as good in assault rifle applications. I would like to see a contemporary version of this round developed. You have convinced me that the ideal solution space for a next generation cartridge lies between 6.0-6.5 mm not 6.5-7.00 mm.

  • Camilo Emiliano Rosas Echeverr

    “we want an assault carbine that performs as an emplaced machine gun”
    What could possibly go wrong?

    • Seamus Bradley

      The power of a howitzer, accuracy of a laser, and size of a pistol.

  • Vitor Roma

    Quite crazy how even the 107gr still manages to have a much better BC than the 147gr 7.62m

  • Colin

    Isn’t this round just a American 6.5×47 lapua . Can someone tell me the difference ? .

    • Colin

      Is this a redesign 6.5x47L SO that no copyright infringement is made so no dues are paid to lapua ! .

      • ostiariusalpha

        No, the Lapua uses a .308/Mauser case head diameter. The .264 USA uses a smaller 7.62x39mm/6.5 Grendel case head diameter; it is essentially a “Super Grendel” with a longer case body.

  • Colin

    Would a heavy 160+ grain 6.5 bullet work better for marksman and Machine guns . But keep your 108 epr lead free super smooth bullet for the rest . I still think this is a 6.5x47L rehash. Target guns to 1km have had success with it.

    • 6.5mm spitzer bullets pretty much top out at 145 grains or so, then they get a little long for spin-stabilization.

      Also, keep in mind that adding 52 grains to the projectile adds 52 grains to the round itself, as well.

      • ostiariusalpha

        There are 160 gr VLD bullets out there (what kind of twist do those need? 1:6?), but that extra weight really would just kill the entire concept of lightened ammunition.

        • Oh yeah, that Matrix thing, I forgot about that. Good point. That can be so heavy because it has a very long shank and is lead-cored. You could design a military 6.5mm bullet this way, I guess, but as you note, the additional weight kind of makes you wonder why.

          • Kivaari

            AND velocity drops if you are using the smaller cases proposed in many peoples minds. Pretty soon we are back at using the 6.5x55mm Swede. A full-powered rifle cartridge suitable for GPMGs, but not carbines like the M4. It will end up being a rifle like the M14.

  • Colin

    What’s the estimated case capacity on the 264 amu (h20) .?. Please.

    • About 48 grains H2O (3.1 ccs), according to my model.

  • Colonel K

    Reminds me of the 6.8 SOCOM debate a few years ago. On paper it beat the 5.56, 7.62×39, and even the 7.62×51. That last claim seemed dubious to me, and made me question the real capability of the round. The .264 concept is hardly new, though. Not only the British toyed with the.280; the US Army almost adopted a .276 intermediate round in the 1930s. The difference this time is significant. The .276 was supposed to be a lighter, less punishing round fired from a higher capacity, lower weight rifle than was finally adopted (the M-1 Garand). The .264 goes in quite the opposite direction, with aided weight and recoil, and the potential for demoralizing the troops who will have to carry it.

    • Seamus Bradley

      Demoralizing? Reflective Belts are demoralizing, not bigger bullets.

    • Kivaari

      The .264 concept is hardly new is an understatement since it has been in use since 1891. Pretty much all of the central European users had a case from which the 7.62×39 was eventually developed. Half of the proposed cartridges use the same case as the 6.5×51-52-53-54mm. The Swede from 1896 used a larger casing. The only thing wrong with those old rounds was the use of long round nosed bullets. There is nothing new being proposed other than smaller cases using good bullets and modern powder so we can get performance that could have been had 120 years ago. Performance, that as I grew up, was called inadequate. Everyone turned their noses up at anything made on a Mannlicher case. The only 6.5mm round having the respect of the masses was the Swede. If it wasn’t a .30-06 or bigger it was “inferior”.

      • Colonel K

        I agree. I just didn’t want to go too far back in time on the subject. If somebody could figure out a way to jam a 90 grain bullet in the 5.56 case and still get decent performance out of it, it might be the ticket, but there will always be problems with any compromise. I do believe that heavy-for-caliber bullets give the best performance, but always at a penalty in terms of recoil and weight. Finding the perfect median may prove to be a fool’s errand, but the quest is always interesting.

  • maodeedee

    It seems to me that 115 grains would be the optimum projectile weight rather than 108 grains. It’s still a significant weight savings while offering better downrange ballistics with a VLD projectile.

    I’m curious to know what the case head and rim size is and/or what the parent case is. Just looking at the pictures next to the 556 and the 308, it looks like it might be a similar size case as the 6.8 spc which is also the same size case head/rim as the 10mm auto and the 40 S&W.

    • The parent case is 7.62×39, so the head diameter is 0.445″.

      • Seamus Bradley

        Would like to see more of a triangular case taper. Part of the reliability of the 7.62×39 is the due to the case taper and ease of feeding and extraction. Not saying it has to be to such an extreme, but a bit more to that of the 5.45mm would be nice and I feel may add to reliability without any real negatives.

        • Kivaari

          The M4 is pretty reliable.

          • Seamus Bradley

            The .264 has fully 1/2 the case taper of the 5.56mm so it may be an issue, especially with rapid fire on a dirty gun in dirty field conditions.

            This isn’t to start some comment war on 5.56 vs 7.62 because that isn’t my point; the 7.62×39 is very reliable cartridge with a good portion of that reliability coming from the case taper. Having a nearly straight wall tube ( .264 USA) inserting into a straight wall tube (i.e. the chamber) in a dirty gun is, IMHO, asking for problems.

            I fully submit that I may be proven wrong here, only time will tell, but there is a reason why cartridge cases are tapered in the first place. This strikes me as being build by a ballistic nerd (I say this with all due respect) and not the Cro-Magnon knuckle dragger 11B that will be required to shoot this round a a ground war with the Russkies. I like the caliber, I like the power, I like the velocity, could care less about the “recoil”, with a polymer case the weight will be no real change, but I would like to see more cartridge taper.

          • Kivaari

            Valid observation.

  • cwolf

    AMU is not in the procurement system. The chance of this round/rifle being fielded is in negative numbers. If anything might move forward, it could be an improved 7.62 round and lighter guns with better sights, etc. Maybe something like a low end Tracking Point Plus.

    Hmmm, remember the Gyrojet cartridges?

    In any case, the drivers in the system are performance, cost, and volume manufacturing issues. Lake City manufactures over a billion + small arms rounds/year.

    Remember, Mk262 and Mk319 are Navy rounds.

    I agree that the Army should develop a weapon system dedicated to Infantry with multiple caliber choices to match the terrain (sort of like the SCAR). Most others might have something like the X95. The Infantry does most of the shooting and killing. The chances of that are slim.

    Realizing Ph/Pk is a function of: the weapon, the sights, zeroing tools, ammunition, and training. Current Army 556 and 7.62 has no accuracy standard. Almost all qualification training is supported KD firing.

    The days of pure Light Infantry are limited. A unit can barely carry the food and water they need, let alone all the mortars, guns, ammunition, etc. It is why folks are exploring ATVs. Lighter ammo is a small part of the overall load.


    • I think you are forgetting that Fort Benning has sent out requirements that appear tailor-made for the .264 USA, and the CTSAS 6.5mm round appears to be based on it.

      • cwolf

        The R&D folks and AMU (to a far lesser degree) spend a lot of time researching possible solutions for weapons. Even DARPA gets involved from time to time (see EXACTO). Caseless ammo has been around as a concept for decades.

        The problem in a sense lies in the assumptions. Do you assume shoulder fired? Do you assume Light Infantry vs Motorized Light Infantry? What is proposed BOIP? Etc.

        R&D (as an aside I doubt if AMU has technical R&D money) requirements are not Big Army requirements. Far different hoops to jump through.

        If you said the 6.5 was going to be a MG or a sniper rifle in some special units like Rangers or SF, then it might be feasible. Then it might grow from there. As an aside I doubt if we’ve seen the bill yet for the stunning overpressure with the .50 sniper rifle.

        New rifle or new MG replacing the 7.62? The criteria the Big Army wants is it must be a big performance increase to justify the cost. And can’t ignore “shoot-ability” (some interesting past failures there).

        It gets complex. A terrain analysis might look at the distribution of inter-visibility distances and ask where a 1,200 m direct fire weapon might have utility.

        I’m not knocking the 6.5 or caseless or any other great ideas. I think the big step forward will be challenging every assumption. Why not a remotely fired tripod mounted 40mm slaved to a headset? Or a sort of 1 or 2 man portable CROW (maybe on an ATV)? True, weird, but why does everything have to be shoulder fired? Why are we trying to squeeze all that complex functionality into a 25 mm shoulder fired weapon?

        The genius I like is the guy who put the 4.2 on a trailer. Park it, lower it, start shooting. Brilliant!

        Sing, dance, laugh.


  • Goody

    Is this not just 6.5 creedmoor painted a different colour?

    • No, it uses a different case head, the same as 7.62×39.

  • Seamus Bradley

    A note on Heat Flux and weight:
    The Proof Research Barrels composed mostly of Carbon Fiber are able to seriously reduce heat buildup of the barrel by allowing for a great heat dissipation curve than conventional all steel barrels. This technology added to a rifle firing the .264 USA would help significantly to reduce the marginal increase in Heat Flux and also reduce weight of the overall rifle itself (note this will most likely increase felt recoil of said round as well).

    Proof research barrels can also reduce the weight of the rifle by over a pound (especially since US Army beefed up the barrel in the M4A1 program for better resistance to heat buildup in high round count/multi-hour engagements)

    It should also be noted that the USAMU 3-gun team are currently very familiar with Proof Research barrels as they currently use them on many of their competition rifles and with great success.

  • Devil_Doc

    6.8, anyone?

  • Padmmegh Ambrela

    How does it compare to 6.5×47 LAPUA and 6.5 CREEDMOOR ? LAPUA is an original design with no parent case while CREEDMOOR is based on .30TC,both built to be easily adapted for 7.62×51 NATO short actions and magazines. Please do an article on 6.5×47 LAPUA,6.5 CREEDMOOR and .30TC and how do they compare to other 6-6.5 mm, 7mm and .30 caliber cartridges.

  • PJKK

    With much better ballistics and a lot less machining to reform brass and make barrel changes they are freaking out of their minds if they simply don’t go with the venerable 7mm-08. But then we all know how they like to waste time and money. So they’ll probably go with their new clown configuration with less sectional density and destructive power within the magnificent 7mm-08.

  • PJKK

    With the right amount of sectional density and flat trajectory the 7mm-08 has a lot more potential, destructive power, and it would not waste so much time, and energy as it would be a lot easier to make barrel changes, and they could basically use the same magazines as the 7.62’s because the case is the same size only necked down to 7mm. Much better than the 6.5’s because of the greater powder capacity and beefier projectiles. the cost of retooling for a half millimeter smaller would be tremendous and makes no sense when the 7mm-08 is so much better of a round. We all know how stubborn some top brass idiots are with their one track minds and how they love to waste our time and resources. Changing to 7mm-08 would be a much more simplified procedure. K.I.S.S. Seriously, pjkk