Modern Historical Intermediate Calibers 012: The .280 British – SPECIAL EXTENDED EDITION

Two .280/30 cartridges, and their immediate ancestors. The .280 concept was inspired by the German 7.92x33 Kurz caliber on the far left, but demands for standardization in testing with the US-developed .30 T65 cartridge (center left) resulted in rounds after 1949 using the same case head as that round.

Two .280/30 cartridges, and their immediate ancestors. The .280 concept was inspired by the German 7.92x33 Kurz caliber on the far left, but demands for standardization in testing with the US-developed .30 T65 cartridge (center left) resulted in rounds after 1949 using the same case head as that round.

Today on an extra special episode of Historical Intermediate Calibers, we’ll be taking a look at one of the most controversial experimental military rounds, one that many believe should have become the standard for the Western World at the beginning of the Cold War. That round is the .280 British, also known as the 7x43mm, and beginning in 1947 it competed head-to-head against the caliber that eventually became the 7.62 NATO in trials to become the standard infantry small arms caliber of the free world. The .280 British has, in the almost 70 years since its invention, become one of the great “might-have-beens” of the small arms ammunition world. Many small arms enthusiasts wonder how firearms history might have been changed if this brilliantly designed British 7mm round had been adopted by NATO instead of the overlarge and too-powerful US-designed 7.62mm.

Was the .280 British really the ballistic marvel that its reputation today suggests? Should it have been adopted instead of the 7.62mm NATO, and if it had been, would development of other intermediate rifle cartridges such as the nascent .22 caliber project that eventually resulted in the 5.56mm have been cut short?

Well, although the .280 is not a poor design by any means, under bright exam table lights it withers a little bit against its stellar reputation. That reputation, and exactly how and why I think it’s not quite deserved, are why I am taking the time to do an extended-length post on the subject. Before we get into that, though, we need to understand what we are really talking about: Chiefly, that the .280 British isn’t just one round, but several. I am not going to get into the history of the round here, because I have a much larger, more detailed post on the subject in the works as part of my series on the US Lightweight Rifle program that resulted in the M14, but let’s take a quick look at some of the different performance variations of the .280 round:

  • Early .280 ammunition used a unique 0.458″ diameter case head, and tests in the last quarter of 1949 showed that it propelled a 130gr steel-cored bullet at 2,270 ft/s from a 24″ barrel. This represents the least powerful .280 round developed.
  • At the same time, 140gr bullets were being loaded in .280 cases by both FN in Belgium and in the UK. Notes from the period cite a muzzle velocity of 2,330 ft/s from a 24″ barrel for rounds of this type.
  • To ease development, the .280 was changed in 1949 to use the same rim dimensions and 0.473″ diameter case head of the US .30 Light Rifle cartridge (which became 7.62 NATO). This variant was called .280/30, and its performance varied depending on the exact propellant and barrel length used. However, for a brief time the objective for this round was a velocity of 2,415 ft/s from a 24″ barrel with a 140gr steel-cored bullet.
  • At the end of 1950, the British augmented the performance of the .280/30 by loading a lower-drag 140gr FN S-12 flat-based lead-cored projectile into the case, and firing it at a higher velocity of 2,595 ft/s*. It was this load that was briefly adopted as the 7mm Mk.1Z in 1951 before the program was dropped two and a half years later. *It should be noted that tests from 1952 list the muzzle velocity of this round as 2,660 ft/s, so the 2,595 ft/s figure may be an instrumental velocity.

It should be understood that there were many more variations than these (and even more test results), and that I have just boiled down the development of the .280 to four representative samples so that we can see how they compare with each other. Astute readers will note that the velocity figures for this ammunition are listed as being measured from 24″ barrels (usually a test barrel fixture). Normally, this would imply that shorter barrel lengths would produce lower muzzle velocities (and therefore less recoil), but a report from late 1949 states that the propellant for UK-loaded ammunition had completed burning by just 13.5″ of travel down the barrel. Test results also back up that early .280 and .280/30 ammunition were well past their optimum when fired from 24″ barrels; virtually no velocity loss is shown when shorter 19.7″ barreled FN carbines were tested. This seems to not be true for the higher velocity ammunition, however; tests conducted in February of 1951 in Brasschaat, Belgium, demonstrated that the 19.7″ barreled FN Carbine No. 19 propelled a 140gr S-12 bullet at over 2,420 ft/s muzzle velocity. Given the date, it seems as though this ammunition was the same as the type eventually standardized as the Mk. 1Z, meaning that ammunition was losing significant velocity when barrel length was reduced.

For the purposes of this article, we’ll be looking at ballistics only for rounds fired from the 24.5″ barrel length, with the addition of a calculation based on the results from the Brasschaat test. Four different loads will be examined, which we will call “Very Early”, “Specified”, “Early”, and “Late”. These will use the performance figures of the four bullet points above, in their respective order. I am also going to throw in 5.56mm M855, 7.62x39mm M43, and 7.62x51mm M59 for comparative purposes. Since there’s so much data, I’ve also decided to make the graphs substantially larger for clarity reasons, so readers will want to open the images in new tabs to see them in full size. Without further ado, here are the ballistics:

Velocity EnergyDrop Drift

So what do these graphs show us? Well, ballistically speaking, the .280 seems to be more like two different rounds than one. The three lower velocity loads with British bullets all have ballistic characteristics that look a lot like the Russian 7.62×39, except with better wind drift and somewhat better energy retention. It’s the Belgian load with S-12 bullet and higher muzzle velocity that looks most impressive, with retained velocity and energy, and wind drift characteristics that more resemble the 7.62×51 NATO than they do the other intermediates. The Belgian load only leaves a little to be desired in its mid-range trajectory, as it has a little bit more drop than the 5.56mm and 7.62x51mm rounds, due to its lower muzzle velocity.

The additional performance of the Belgian load (which later became 7mm Mk.1Z) didn’t come free, however, as testers at the time noted that the more powerful ammunition susbtantially ruined the favorable fully automatic characteristics of the guns firing it. In service to a future post, I created a spreadsheet detailing the recoil characteristics of different .280 British loads and other comparable ammunition, and I might as well share it now, so click the link here to download it. A graph from that spreadsheet, showing recoil energy figures assuming a seven pound baseline weapon, is below:

Recoil Energy

It’s pretty obvious that the later .280/30 British/7mm Mk.1Z load produces substantially more recoil energy than other intermediate caliber weapons. Versus the sometimes challenging-to-control 7.62x39mm, for example, it produces 42% more. However, even the turbocharged Mk.1Z still produces significantly less recoil energy than the larger 7.62 NATO.

One of the things I wanted to help convey in this post is the size and weight of .280 British ammunition, in particular how much larger it is than most other intermediate cartridges. To this aim, I took a few close-up photos of one of my .280/30 cartridges – with a pink tipped “Type C” 140 grain steel-cored bullet – next to other rounds it is often compared to:


A lineup of some intermediate calibers: .280/30, 7.62×39, 5.56mm, 6.8mm SPC, 6.5mm Grendel, 7.92x33mm Kurz. Note how much larger than all the rest the .280/30 round is. Its size is indicative of its significantly greater bullet weight and case capacity versus all the other intermediates shown here.



Sometimes it is claimed that had the .280 British been adopted, there would have been no need for the 5.56mm caliber. Speculation aside, the .280 British is more similar in every respect to the 7.62 NATO than it is to the 5.56mm.



The .280 British is often compared to both the .276 Pedersen and the 6.8mm Remington SPC. In most respects the former comparison holds true, but when compared with the 6.8mm the .280 as it was adopted is substantially larger, heavier, and harsher-recoiling.


It’s can be very difficult to make an accurate size comparison from just photos, especially given the small camera lens I am using, but hopefully these illustrate that the .280 is really on the very upper edge of what would normally be considered “intermediate”.

The .280/30 is a pretty heavy round by intermediate standards, as well; the round shown above weighs 20.8 grams, 21% more than brass-cased 7.62×39. For additional reference, that’s 73% more than the later 5.56mm, while the 7.62x51mm it competed against weighs only 16% more. The British did investigate reducing this weight, however, as the orange-anodized aluminum cased round in the title card demonstrates. That round weighs substantially less, at 14.5 grams. Unfortunately, aluminum case technology never did pan out, although research was conducted for several decades by both the British and Americans.

OK, so with all that done, what do we make of this British .280 caliber? Well, it’s not a bad round. In fact, in a strictly technical sense, I would say it probably was the better concept, versus the American .30 caliber that became 7.62 NATO. However, it seems to me that conflation of the early, more sedate loads, and the later high-performance ones has given many the impression that the .280 was some kind of wonder-round that could do everything and at the same time kicked like a kitten. That is not true.

Should the .280 have been adopted? No, I don’t think so. Although the round was conceptually superior to the American .30 T65, British development of the round experienced significant and lingering problems. The caliber was plagued by poor accuracy when loaded with British steel-cored bullets, and the Belgian S-12 projectile, although relatively low drag and possessing generally excellent characteristics, lacked the ability to penetrate steel helmets beyond 700 meters. In addition, the more heavily arced trajectory of the .280 was never fully ameliorated, except by even larger and more powerful abortive 7mm variants of the American .30 caliber. For these reasons, the American, French, and Canadian delegates to NATO expressed their preference for the .30 T65, and even the British delegates did not commit fully to the .280, instead suggesting the Organization adopt both. Had the Americans embraced the .280 concept and injected more funding and manpower into the effort, maybe it could have succeeded, but even by 1949, when the .280 was still in its infancy, the .30 T65 was already nearly perfected, having had a three-year head start on the British effort. NATO had no reason to choose a less developed, riskier caliber, and the pressure to standardize at all costs was high. Although the choice of the .30 T65 is disappointing to those of us who wonder what could have been, at the time it was probably the right one.

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 can be reached via email at


  • John Yossarian

    Best article of the series so far. I think it’s clear from the recoil graph that 5.56 NATO would still be necessary for full-auto infantry operations. But I do think that a perfected .280 British – or 7mm-08 – could have bested 7.62 NATO.

  • Ευστάθιος Παλαιολόγος

    Thank you sir for these articles!

  • This is great stuff. Myth busters of the ammunition world.

  • kyphe

    The .280 though generally better suited in my opinion as a basic infantry round than the 7.62 NATO, Is still too big and bulky to prevent the development of something smaller. The fact that we have Russian 5.45×39 demonstrates this pretty conclusively as far as I am concerned. I Am of the belief that the adoption and continued development of the .280 may have actually sped up the development of smaller cartridges and we could be using something more like the Grendel as NATO standard today. Where the .280 could have really had the opportunity to shine was use in the light and general purpose MG role like the TADEN.

    • I rather think we might instead have seen some wicked SCHV rounds loaded to the same OAL. As you say, if the Russians felt that 5.45 gave enough benefit over even the modestly sized 7.62×39 to be worth adopting, there aren’t many intermediate configurations I can think of that would have prevented SCHV rounds from coming into vogue.

  • UnrepentantLib

    Thank you. I’ve been waiting for this post. You make some good points, particularly that choosing the T65 was the right decision at the time. Sometimes “good enough and ready now” beats “fantastic, but it’s going to take a while.”

    • Yeah, there’s no denying the .280 had more promise, but people forget what an absurd lead the .30 T65 project had even by the time the .280 was first demonstrated in America. If there had been more funding available to the British team, maybe they could have made up the difference, but as it was, no chance.

  • 40mmCattleDog

    I love this series dude, it just shows that while far from perfect and mired in tradition and bureaucracy, the U.S. military’s selection of firearms and calibers is a logical progression from combat experience (i.e. the M4A1 and 5.56 and all their advantages vs larger weapons and calibers).

  • James Young

    If anything this is is a pretty convincing case for the 5.56×45, but is it fair to compare the 5.56×45 with a 20″ barrel instead of a 16″ or 14.5″?

    • You mean when comparing it to 7.62×39? That will come. 🙂

      • James Young

        I just mean in general since the Army seems to be dead set on M4s. M4s will eventually trickle down to the Marines too, so that seems to be becoming the standard.

  • UK Bob

    Thank you for this series. Good to get the historical perspective. When I was younger this one (and the bullpup) were almost mythological might-have-beens.

    I might have missed a mention of it, apologies if I did, but there was another attempt at getting a UK cartridge (and bullpup) adopted as a NATO standard in the early eighties. This time the calibre was 4.85mm.

    Obviously the winner of that NATO competition was 5.56mm, so technically you could argue that 4.85mm was not in fact an ‘intermediate’ calibre.

    The UK duely adopted the SA80 in 5.56mm NATO and had a few teething problems until our German friends from H & K (then part of BAe) lent their not inconsiderable engineering expertise and fixed it. Luckily not with plastic !

    http://www.militarycartridges {dot} nl/uk/4_85mm.htm

    • The (normal-length, sorry) article on the 4.85mm is already written and scheduled. It goes up Monday. 🙂

      • Colin s

        Have you done anything with the 6.25mm briefly developed before the 4.85mm?
        As I understand it that too showed great promise (like 280) but ’77 nato trials had upper limit of 5.56 so it was dropped in favour of the daft looking 4.85mm.

        • I haven’t. The 6.25mm is very hard to find, and information on it isn’t much easier.

          • 91-110gr projectile at ~2,680fps
            Mean peak pressure no greater than 50,000psi
            Cartridge weight: ~238gr
            COAL: 2.48″

          • Colin s

            If you are interested in looking into it, I think Anthony Williams has more info than what Daniel E. Watters has posted.

          • I have his book. He’s got a little bit, but… Well, I’d still like to get a sample first. 🙂

        • FWIW: The decision to try a 5mm projectile was made as early as 1970.

  • Renato H. M. de Oliveira

    I’m unable to download and open the recoil tables, but I’ll give a shot – stupid, probably, but I’ll try anyway.

    It seems that the upper limit for a relatively easy full auto control would be the original intermediate – 7.92×33. Its figure is around 6. 7.62×39, as you stated, may already be too much, and most calibers handily beat it.

    If my primary goal is a controllable caliber for full auto, wouldn’t 270 Brit closer to the ideal? There would be obvious setbacks in other areas, but life is a constant conflict of interests.

    • It might be that I screwed up and uploaded the .ods file instead of the .xls file. Let me check.

      • Renato H. M. de Oliveira

        Now I downloaded it, thanks.

        Interesting that 276 Pedersen would recoil pretty much the same as 6.8 SPC in a modern rifle.

        Wouldn’t 270 British with a decent projo be a good long range caliber?

        • Depends what you mean by “long range”. For what it’s worth, with a low-drag 125gr bullet fired at 2,600 ft/s, the .270 British would be approximately equivalent in trajectory, wind drift, and velocity retention to 7.62 M118LR.

          Now, I’ve shot a little bit of 175gr .308 at distance, and I personally wouldn’t call it “long range” ammo, more like “medium range”. To me “long range” implies something that gives you significantly better pH beyond 800m, and M118LR in my experience has a tough time beyond 700, where it starts going transonic. It’s not like you can’t make hits beyond that range with M118LR, but there is a much, much bigger difference in making hits with a .300 WM and M118LR than there is between M118LR and an M80 equivalent, for example.

          But all that aside, while I wouldn’t expect a hotrodded .270 to be challenging .300 WM, it seems like it could be made pretty equivalent to M118LR.

          • Renato H. M. de Oliveira

            Defining long range is indeed challenging.

            270 Brit can match M118 with much lower weight and recoil, but then again neither can be seen as true long range replacements of the 30-06.

            In fact, in my humble opinion, armies of the day still wanted Civil War rifle range with post-WW2 efficiency in arty, armour and air support – a nonsense. Much better have a different CONOPS placing more importance in foot soldiers’ mobility and a more liberal use of heavier assets than having foot soldiers regularly needing to hit targets beyond 500 m.

    • I changed it to the correct file. Go ahead and give it another try.

  • Big Daddy

    From a military perspective they had it correct pretty much in WWII. The world was at war and they needed to fill a lot of needs as fast as possible and they did on both sides. After the war they tried to save money and do the always fail one size fits all. They spent so much money they would have been better served to just leave it be. But for some reason the military mind cannot see troops armed and equipped differently, they want to see row after row of exactly the same soldiers. The DOD even tried to make boots that could be worn on either the left or right foot. I wonder how much money they wasted on that one? Not to mention the whole camo affair of the last 15 years, a major waste of taxpayer money and DOD resources.

    You need a pistol caliber handgun, the modern 9mm is fine for a handgun. Hey DOD use the Glock 17/19/26/34 or SIG 320 in 9mm and call it a day. Next you need a carbine for troops that are not infantry, sort of like a PDW that can engage out to 200 meters minimum and better out to 300. Low recoil, inexpensive to manufacture and effective, simple to operate and repair, hey that sure sounds like an AK47. In WWII the M1-M2 carbine was perfect for non-infantry and rear echelon troops. Me thinks the M4 is perfect these days. For infantry 5.56mm is just not enough, especially in shorter barrels, it was designed to work with longer barrels and at higher velocities. A true intermediate between a 30,06/.308/7.62×51/7.62×54 and a 5.56mm/.30cal carbine/ 7.62×39 which is an intermediate round between the full size and a pistol cartridge.

    So what an Army needs realistically for their troops to be properly armed was pretty much what they came up with in WWII. Yet for some reason they seem to think it’s not a good idea due to total bullshit bean counters who never saw combat let alone never handles a firearm other than to qualify if they even do that, sort of like the average USA police person.

    You need a handgun, a carbine/PDW type gun, a main battle rifle, a SAW and a GPMG, as well as a Sniper/Squad Marksmen rifle in the same caliber as the GPMG or even more powerful. Not to mention effective calibers and weapons for special forces use, like suppressed weapons. Don’t get me started on other weapons like anti-tank and anti-personnel like the 40mm grenade and LAW/AT4 type weapons. The army seems to ignore the needs of the basic infantry platoon. The Marines try but with limited funding.

    • I would argue the jury’s still not out on whether the M4 is not enough gun for the infantry. It certainly seems to be enough gun most of the time, and even when it has problems, the blame seems to be more on tactics, ROE, and training than equipment.

      The argument that the M4 loses too much velocity seems to be thin, as well. We can see the relationship between the M4 and M16A2 in this graph from an earlier post:

      I have the data that was made from, as well, and M855 stays above 2,000 ft/s for only 65 more meters from the M16A2 versus the M4. One could argue this is significant if we are talking about catastrophic fragmentation thresholds for M855, but now M855A1 is in service, and it has a much lower frag threshold and ballistics designed for the M4 specifically. So if it ever was a problem, it seems to be less of one now.

      And of course, more “bang” would be better, but let’s not forget the cost in recoil and weight, which the data tells us will be significant. I think before any increase in ammunition size and weight is accepted, things like the paper Rifle Squad Armed with a Lightweight High-Velocity Rifle, which shows that reduced rifle and ammunition weight and recoil really do give a huge advantage to the infantryman, at least at close ranges.

      Finally, we also shouldn’t lose sight of the fact that war is a combined arms effort. If the infantry are being outranged by Pashtuns, is the right solution a new, larger standard caliber, or maybe something else? I did the math a while back on how many Pike missiles a platoon could carry for the same weight as switching to a bigger caliber, and the answer (9 or 10 missiles per grenadier for the same increase in weight) really makes one wonder if investing in guided high explosives isn’t a much better idea than trying to augment inert rifle calibers.

      • Kivaari

        The missiles seem to be a wiser choice than changing the rifles. The M4 seems capable of doing pretty much the job that needs doing. Those trying to make every rifle into a long range rifle seem to miss the point of how the M4 is used. If I were changing things, it would be simply to adopt a mid length 16 upper and call it good. Would it be worth it? Not likely, but it’s what I like.

      • Big Daddy

        As I said for most troops the M4 is fine but for the guys having to face the enemy in a firefight as their main job they need something a little more powerful but not as much as the .308. Notice the Israelis realized the Negev in 5.56mm just didn’t cut it and a few army’s are going with a 7.62/.308 SAW. A mix of a a .308 battle rifle and SAW along with the M4 within the squad works but again as I said the Generals hate it when all the troops don’t look exactly alike. They just could not handle it in a parade or formation all the different gear and arms. That is their mentality and having been in the Army I saw it many times, it’s like OCD for officers or something. I was a scout and drove M113s, ITVs, M577 vehicles and the M16 and M203 were by far the worst for mechanized troops, it was not the weight it was the length. You cannot shoot them out of a cupola. I did carry a M3 Grease gun and for a driver it was the perfect weapon, again the need for a PDW. One reason the Israelis went to a bullpup, most all of their troops are mechanized. My point is one size does not fit all and for some reason the DOD keeps pushing it, it’s a fail on many levels. Especially for the average combat troop just trying to stay alive and do their job. The light weight M4 is pretty good if you are on a team or crew served weapon but not for a pure infantrymen. In an infantry squad guys like a grenadier, assistant gunner, the lighter weight is appreciated but when you are getting attacked by a determined force the heavy hitting round is appreciated. They are always trying to improve lethality of ammunition which is as it should be but they just do not admit its limitations and a shorter barrel AR has many, although it looks a lot less with the M855A1. An infantry squad should have a SAW in .308/7.62 and at least 2 other soldiers/Marines with a rifle in the same caliber. Modern .308 battle rifles are not much more in terms of size and weight over a M4 these days but offer so much more to the infantry squad.

        • In the US Army and USMC, at least, they’ve gotten something more effective, the new EPR and SOST rounds. These have both better effective range and better terminal ballistics than M855 does.

          The thing with SAWs that people ignore is that the concept has changed, and that is why many armies are considering switching to 7.62mm. The original SAW was primarily designed to augment the automatic firepower of the squad, and to a much more limited extent augment its range. Now, the SAW is being used in much the same way a GPMG is, and so more militaries are looking at replacing them with GPMGs (the NZDF, for example).

          In fact, this creates an interesting question: If we are replacing the SAW in the squad with a GPMG – which allows only half the ammunition to be carried – because the additional range is useful, then how do we augment the automatic firepower of the squad? Switching to a larger rifle caliber run counter to this, because the larger caliber produces more recoil and heat, and weighs more, so the infantry rifles are less able to take up the slack of the SAW than they were before in 5.56mm caliber. So now, with a heavier rifle and SAW round, we have substantially reduced the automatic firepower of the squad. Is that a good thing? It doesn’t sound like it. Maybe the answer, then, is a new more capable but still relatively lightweight caliber for belt-feds, and a caliber very much like 5.56mm for rifles, coupled with additional training to allow every rifleman to act as an automatic rifleman if the situation demands.

          • ostiariusalpha

            Like a polymer case telescoped 6.5 caliber GPMG?

          • My hope is that you could make something smaller and therefore lighter than that, but if not, then yeah, I suppose.

          • ostiariusalpha

            Well, Ms. Phillips has indicated that a future 6.5 CT would have a smaller casing than the 15.36g version cobbled together from the 7.62 CT. Who knows how much that might weigh?

          • About the same. The reduction in weight due to a reduction in case size would be negligible.

            I mean, the case weight for the 15.4g CTSAS 6.5mm is like 4.9 grams, so even if you reduce the weight of that case by 10%, then you get the round down to 15g, maybe a little less.

          • ostiariusalpha

            Plus propellant. I could easily see it dropping down a couple grams with a smaller, more efficient case.

          • Um, there are not any more than a couple grams of propellant in the cartridge.

            Look, let’s break it down:

            Total: 15.4 grams

            Bullet: 8.1 grams

            Primer: 0.35 grams

            Propellant: 2 grams, maybe more.

            So then the case plus plug weighs 4.95 grams or at least close to that. I don’t see the propellant going below 2 grams at all (for comparison, 2 grams is 30.86 grains, and 6.8 SPC uses a charge of about 30 grains, so I’m already lowballing this), so then we just have the case. And that case is not coming down by 2 grams!

          • ostiariusalpha

            The 6.5 CT case currently uses a 7.62 charge weight, so I’d aim for going from 3.25g down to 2.5g of propellant (just under a 6.5 Creedmoor charge weight) or even 2.25g. Then reduce the case weight from 3.66g to 2.5g. Depending on how much velocity you need, you can get those 2g off if you want to.

          • Erm, what? Where did you hear that they use the same weight of charge as 7.62? I find that very unlikely, and actually probably impossible as the ogive length of the 6.5mm is much longer, so the propellant container has to be smaller.

          • ostiariusalpha

            Pfft. Use some logic, Nate. 6.5 CT has a 8.1g bullet and 7.62 CT has a 8.42g bullet; there’s a .324g difference between them. The 6.5 CT cartridge is 15.36g and the 7.62 CT is 15.55g; which is only a .1944g difference. Subtract the bullet weight difference, and the 6.5 CT components are actually heavier than the 7.62 CT. If the powder charge was as reduced as you suggest, then the weight difference would have to be made of even more by the polymer casing. Which is an irrational suggestion, they didn’t make the case walls or case plug extra thick for your convenience. The ogive is longer on the 6.5mm projectile, but it also has a sectional area at the shank 14% smaller than the 7.62mm; it’s not hard to see how it would make up the difference there, unless you’re truly obstinate.

          • You’re going to make me use SolidWorks to prove you wrong again, aren’t you? That will have to come later today, I am AFK right now.

          • ostiariusalpha

            Your SolidWorks didn’t add up last time, remember?

          • You mean it didn’t cut as fine as your hair splitting? That I will admit.

            So, hold on a sec, why exactly do you think they wouldn’t make the case walls thicker? They are using those external dimensions to allow compatibility with the already-developed 7.62mm LSAT LMG with just a barrel swap. The ballistics of the round are similar to the .264 USA, which means either necessarily a smaller propellant chamber or a lower propellant charge (and thus pressure). There’s no evidence at all to suggest that the round would use the same propellant charge as 7.62 NATO…

            It’s not like there’s not precedent for this either, check out page 9 of this presentation:


            So the thing you said they would never ever do is exactly what they did during the 5.56mm round’s development. Indeed, this page all but proves that is exactly what they did do with the 6.5mm CT round, as one notes that the concept doesn’t work quite right if you use a less dense propellant load.

            Anyway, here’s our sketch:


            You can see I have just thrown both the outlines for 7.62mm and 6.5mm CTSAS into one. Note how much more volume the 6.5 CTSAS takes up, even with the same case wall thickness. Also note how much more case material there is, and therefore how much heavier the case would be. Let’s find out exactly (note that I am using nylon as a placeholder material – it also happens to be conveniently transparent)





            So the 6.5mm case, even with the same wall thickness, is about 13% heavier than the 7.62mm case. I am not confident that my material densities are accurate here, so instead I am going to back-calculate what that means for the propellant load:

            15.5 grams – (130 grs / 15.43 grs/g) – 0.35 g (primer) – (reduced propellant charge) 2.65 g = 4.075 g case weight.

            4.075 * 1.13 = 4.605 g

            So now,

            15.4 grams – (125 grs / 15.43) – 0.35 g – 4.605 g = 2.343 g charge weight, or about 12% less propellant, just based on weight alone. It could be even less than that.

            Now let’s look at the propellant chamber volume in our respective cases:





            The 7.62mm round has only 5% more chamber volume, where it should have 12% more. This analysis indicates that the case walls for the 6.5mm CT round are thickened versus the 7.62mm version.

          • ostiariusalpha

            Meaning that you got it fundamentally wrong, and the case volume turned out to be nearly identical to a .30-06. Yes, that hairsplitting. 😉

            “Indeed, this page all but proves that is exactly what they did do with the 6.5mm CT round…”
            The difference between the two 5.56 CT spirals was visually obvious, there was no secret that the case walls were altered. That’s not a terrible example, even if it doesn’t match what any of the Textron literature says. Occam’s razor would suggest though that the simplest explanation is in the cartridge plugs, with the one for the 6.5 CT simply having a larger volume of polymer than the 7.62 CT. Your SolidWorks were pretty solid actually, the 6.5mm cartridge looks pretty similar to the Textron cutaway diagram, though you seem to have left out the thickening in the case web.

          • Interestingly, this analysis also indicates that the CT cases are made of PPS.

          • Ευστάθιος Παλαιολόγος

            Great discussion here! Though in no way anywhere near as scientific or well though after as yours, I have also wrote some articles on the subject in the local (Greek) defense press.
            The way I see it is that larger isn’t always better. If it was so arming all of the Squad with a .50cal would be the answer. It’s not though…
            Also, Infantry fighting is not riflemen duels. And not all wars are Afganistan. An Army should be preparing for the big war, even if the big war (near pear or pear opponent) is the least likely. Big wars don’t wait for you to adapt. Counter insurgencies allow an army to adapt, or don’t have immediate devastating effects if you are not 100% ready. Big wars though have.
            Having said this, from my point of view, the biggest problem for the rifleman that prevents him from being effective at longer ranges is this, inability to see the target at longer ranges, inability to identify him as target when he sees him, lack of general situational awareness, and inability to aim and hit something beyond a few hundred meters. This must be viewed in the context of ground combat. Where the individual soldier tries to avoid being killed, there’s fear and stress, poor visibility, lack of information etc etc etc.

            Being a rifleman I hate to admit, but I must, calibers and rifles little have to play in winning or loosing. Infantry fight is more about heavy and crew served weapons( ATGMs, Mortars, HMGs, AGLs, Light Cannons etc etc) plus the combined effects of other arms like (and especially) Artillery and Air Assets.

            But the rifleman needs a gun and caliber that will help him do his real work, the last few meters to the objective. An easy to use, easy to maneuver with weapon with accessories that make easier to aim and shoot, because that few last meters wont wait for anyone to take his time in order to control his heavier weapon.
            Also, even if the actual combat is strictly foot fighters still, there are weapons suited best for every role. Longer ranges, MGs and Sharpshooters etc. Longer ranges give “more time” to the opponents. CQB and shorter ranges, rifles with controllable caliber. At longer ranger fewer heavier weapons do most of the work. Rifles support of maneuver. Shorter ranger, rifles do most of the work and the other weapons support.

            The only thing I actually found as a real issue in favor of the 7,62X51 in my articles was the issue of what is considered as cover for the enemy. Larger-heavier bullets have less problems with obstacles in front of the target.
            Sorry for the long text. Again, great conversation!

        • CruisingTroll

          Actually, for the guys facing the bad guys in a firefight, FIRE AND MANEUVER is the name of the game, THAT’S the lesson they learned from WW2. The vast majority of rounds sent downrange are there to keep the other guys’ heads down. So having more ammunition is far more important than being able to punch through a steel helmet at 750 meters. You’ll notice that the guys in Iraq have very rarely been calling for more range. Why? Because they usually had the full combined arms thing going. If some Bogies are plinking away at you from 900 meters with their Mosin-Nagants or Dragunov’s or what have ya, you don’t fart around maneuvering to engage. You tell the crew of the Bradley to light the SOB’s up. Problem solved. Afghanistan is, in the world of warmaking, an anomaly. Wide open spaces that are not friendly to combined arms. Were it not for 9/11 and Al Qaeda going to ground there, nobody would give a damn about the place, ’cause there sure as shinola isn’t anything even remotely significant to our national interest there anymore.

          If you want to refight the last war, then sure, focus on getting heavier, longer range, lower ammo capacity weapons in place. If, on the other hand, you want to fight a modern combatant over most of the relevant terrain in the world, then the intermediate caliber round is the way to go. Because in 95%+ of your firefights, anything out past 500 yards is the domain of the AFV and artillery. Snipers excepted, of course.

    • CommonSense23

      5.56 is plenty for a service rifle. With the current rounds available even for SBRs. And 5.56 is plenty for a SAW.

      • Big Daddy

        It wasn’t enough in Afghanistan and many army’s are going back to 7.62/.308 SAWs. As well as integrating that round on the squad level because of lessons learned. Those lessons it seems people will not accept. Kind of the reverse of what happen when they wanted to go to an intermediate round and everybody said no we need a full size round, y’all are wrong on both sides, we need both. In Iraq one guy with a .308 sniper rifle held a whole enemy in check in an area for the US Army. One guy and a rifle, so please nobody tell me the 5.56mm is enough when time and time again the job is done by a .308 that the 5.56mm could not do.

        • Kivaari

          I am curious what the actual record of the 5.56mm DMR has shown in combat. It seems the bigger limiting factor on any rifle has been the optics. Good glass on a 5.56 (a known accurate rifle and cartridge combination) should be pretty good. That’s not saying a 7.62mm or .300 WM doesn’t have its place as they certainly do. But I suspect the DMR proper set up with good glass will hold its own in the right hands.
          All I’ve read about the 7.62 caliber semi-automatic sniper systems has been pretty much, they shoot unreliably. That seems to be backed up with civilian experience, where most people report the self loaders are unreliable. What’s the truth. Do we have an inaccurate self loading 7.62 and an accurate and reliable 5.56 DMR. Do we need a new one, considering it is more a degree of skill than cartridge?

          • Here’s “somebody” making good use of a 5.56mm DMR at 800m:

          • Kivaari

            It looks like he got some.

          • FarmerB

            Interested in your comments about SASS unreliability. As a civilian, I run a couple, and we’ve (shooting mates as well) have never had a problem with them. Loaded with the correct bullet (normally 175 HPMK) they are pretty effective out to about 1000m. Biggest problem is that they aren’t cheap.

          • Kivaari

            I’ve talked to several owners and dealers that reported the same trouble. Kyle’s book mentions it. Several magazine articles have as well.
            Most significant has been my local dealer that has sold or owned all of them, and his personal and customer experience has not been good.
            I can’t shoot them due to the recoil. A broken neck limits me to weenie calibers. It’s a major reason I have invested so heavily in the AR15 in 5.56. Even though I was issued the M16A1 and the M4 I’ve used them more now that I have retired. They really grew on me.

          • FarmerB

            Thanks – so it’s somewhat specifically talking about the models deployed by US forces? M110 SASS, Mk20 SSR and the like? Hopefully the new CSASS works better for them.

          • Kivaari

            Yes. The print sources were all mentioning the actual rifles in use. Each source commented that they were not reliable. Users went back to bolt action rifles.

        • CruisingTroll

          See my above regarding FIRE & MANEUVER. What is handy against insurgents is not necessarily the same thing you need against opponents equipped and using modern combined arms.

    • DIR911911 .

      that’s why marines kept the barrels as long as they could , they knew with the 5.56 velocity matters

      • Actually, they just switched to M4s.

      • Kivaari

        At the time I think it was simply budgetary. The M16A2/3 rifles were paid for and in place to be used. Considering they are damned fine rifles I could sure see them waiting until there is money in the budget.

        • Yeah, it’s funny that people assume the Marines kept those guns because they had some super secret Oorah wisdom the Army knows not, when from how I understand it, actual combat Marines had been clamoring for the M4 for years (not the least reason for which being their collapsible stocks).

          I’m not against longer barrels on infantry rifles, mind you. In fact one concept I think the US military has criminally ignored is the “back end only” carbine, that being a 20″ barreled gun with the stocks and other hardware of an M4.

          • roguetechie


            Yeah I’m extremely happy with my 20 inch uppers and 6 position stocks.

            I have a couple 16 inch uppers and a couple 18’s with shortest gas systems being mid lengths.

            I run mostly duostock and the pardus cheapy SOPMODS, though I’m contemplating some other options.

            I’m sure some will recoil in distaste and disgust at my stock choices, but guess what? I got a bunch of duostocks for $10 each on closeout, and the Pardus was my default choice when I ordered lowers for a long time… Point being, they work for me and I didn’t have to spend small fortunes for them.

            *the duostocks may get a face lift and other cosmetic surgery to make the toe less… Massive.

            Also a couple of the AR’s are probably going to partially finance an AUG purchase.

            On this note, how do you guys feel about the classic scoped AUG setup versus the railed option?

  • Kivaari

    It’s too bad the velocities, and all the data that flows from that, is from a 24 inch barrel. Even in that era it would be unlikely to have a service rifle with a 24 inch barrel. Even though it said it achieved max velocity in a shorter length, the Brits should have used a realistic length test tube.

    • ostiariusalpha

      Yeah, but they could get away with the longer barrel because the No. 9 was a bullpup; and still lighter than the M14.

  • Kivaari

    This is a great series. Thanks for all your efforts.

    • Thanks to everyone for reading, I mean it.

      • c4v3man

        It’s one of the best things going on this site, and it’d be interesting to see the series compiled into a book with perhaps a little more detail, or simply a collection of your best articles for electronic publishing through Kindle and the like. Give us a chance to buy you a coffee/beer for your efforts.

        • Well, that’s a possibility, but in the meantime just share the link and that helps pay my bills. 🙂

          • Cordite

            I agree, I would purchase a book based on this series and SCHV rounds and such in general from you even if it was $30-50.

            Nathaniel, I would like to see you do some articles on what you think would be an ideal round or selection of rounds for the military based on your years of study. Perhaps do another article where you come up with some experimental designs you think would be ideal if no current real life offerings fit your criteria.

            My guess is you would develop a round close to the size of the 5.45×39 with better ballistics. Or would you go with something larger if we weren’t constrained to the size limits of the standard AR15 magwell? I’m curious what you would go with for a larger caliber round to fill the machine gun and sniper/dmr roles, as well.

            Thanks for doing these articles. This kind of content is what keeps me coming back to tfb.

          • Kivaari

            Wouldn’t the better round than a 5.45mm, simply be the 5.56mm? It seems that the defect in the 5.45 isn’t really much beyond the bullet being so tough. Simply by being so solid in construction, without the fragmentation aspect found in the 5.56mm it’s pretty good. The 5.56mm is a great round in its newer versions. The addition of longer, heavier and accurate to greater distance projectiles makes it pretty damn good. The 5.45mm is a well designed round. The thick rim to resist rim tear through, the straighter case (compared to the 7.62x39mm) and the long bullet made it into a better round than its predecessor. The biggest improvement they could make, beyond a fragmenting bullet, is to put it in a rifle with better sights. A Galil-Valmet styled rifle would make a huge improvement.

          • Hi Cordite,

            “The ideal caliber” is the question that got me interested in this subject in the first place, so I’ve thought quite a lot about it. As evidence of this, let me share a screenshot of my SolidWorks folder:


            Given that, I was asked this question in an email recently, and this was my response:

            “The strongest, most important point I have to make is that it is vital to get the next small arms ammunition configuration right. We will be stuck with the next configuration for many decades, and small arms ammunition is much more important to the fight than the planners of the Cold War assumed, so for the infantry it is vital This means setting aside our preconceived notions, setting aside the elegant concepts, and setting aside our egos most importantly, and attacking the problem from first principles through extensive research and empirical testing. If anything, this is my biggest criticism of the Tony Williams GPC idea that seems to have snowballed recently. His concept is entirely based on theorycrafting and supposition, with no real foundation in field research and empirical testing. Others (including myself) have added to his concept with additional models and the occasional wildcat, but it’s a far cry from what’s needed, which is a complete, ground-up research program to attack the problem both from an infantry capability perspective, and from an empirical performance perspective. As examples of both of these, here are two questions we have not answered:

            “1. How much additional capability is afforded by the introduction of optics? What’s needed to answer this is a test whereby units equipped with MILES gear or some similar simulators capable of long range marking perform exercises and mock combat against each other, and the effectiveness of units equipped with optics or not equipped with optics is compared.

            “2. How much actual additional capability would a 6.Xmm intermediate afford? We know figures like retained energy (calculated using things like JBM’s calculator, not using actual drag models, mind you), velocity, etc, but we do not know how the actual rounds would perform. At 800m, against an unarmored Pashtun, would you be able to perceive any difference in lethality between the 6.Xmm and 5.56mm or 7.62mm? If you could, under what circumstances do those differences become apparent (e.g., if the target is hiding behind a barrier)?

            “I bring this up, because my “backing a horse” so to speak would be a great mistake. It would take away from my message, that everyone needs to back up and try to build from the ground up a picture of what the needs of next-generation small arms and the infantry really are (including in a combined arms context). If I said “oh, my pet caliber is a 5.92×47.5mm SCHVGPC thing”, then I’ve done the very thing I criticized others for. Another advantage to not endorsing or condemning any one concept is that I am free to explore all of them, which I do on a regular basis. I can be open and create a dialogue with people about 6.5mm GPCs as easily as I can subsonic .30 caliber rounds, or 5mm SCHV cartridges, without seeming a hypocrite. I’ve seen that happen many times to both the 6.5mm Grendel and 6.8mm SPC communities; once they got locked in to one cartridge or another, they couldn’t justify exploring anything else.”

            Having said all that, I do genuinely believe that a two-caliber system is less risky than a single-caliber system. What exactly those two caliber should be is anyone’s guess, but I think single-caliber systems invite substantial risk of “getting it wrong”, where systems with more calibers are more flexible.

          • Doctor Jelly

            Printing shirts that say 5.92×47.5mm SCHVGPC right meow!

  • roguetechie

    Call me weird, but I’d really like 960 meters / 3150 feet per second out of an 18 inch barrel from something like a 5.45 style round.

    Is it any one thing that makes me want this? I’m not certain, but instinctively and from my knowledge, I just prefer it.

    • You can probably hotrod 5.45 to do it.

      Otherwise, there are .22 cal wildcats of the 6.8mm that would do that easily.

      • roguetechie

        I know this is probably going to sound really odd, but do you think a 5.56 FABRL bullet in a cbj-ms style sabot loaded into a 30 carbine case to no longer than 5.56×45 COAL could get to 900-960 meters per second muzzle velocity?

        If so, could it do it without breaking 50-55k psi peak pressures?

        And if so could it do it with a 16-20 inch barrel to work with?

        I ask because a friend and I are trying to work out what you could basically describe as a 5.56 minimum cartridge. The idea being, just how light can you make a cartridge with acceptable performance without resorting to case telescoped cartridges. If it would be possible to have a saboted FABRL bullet in a 30 carbine case and not load past 5.56 COAL it could result in more capacity in fractionally shorter magazines that you could carry much more of. I also believe it would probably be easier on barrels and other internal components, and more controllable in full auto.

        Seems to me this could be a good way to have our cake and eat it too.

        As an aside though it would be interesting to know if you could get your nose cap sabot CT idea to work with an equivalent reduced diameter and the same FABRL bullet. I doubt there’s enough information available to tell at this point though.

        • What weight bullet were you thinking for this? 37gr?

          • roguetechie

            Yeah let’s say 35-40 grains with 37 being the ideal.

            Do you think it’s possible?

          • Yeah, probably.

        • gunsandrockets

          I think that is an excellent idea.

          Such a low pressure cartridge with such a stubby case might also work very well with a delayed blowback action.

          • roguetechie

            I hadn’t considered delayed blowback so much as just a modified AR15 as test bed. The idea being that a 5.56 minimum round with better flight characteristics to compensate for a round that, in total, weighs half or less than half the weight of a loaded 5.56×45 round.

            Additionally, the better flight time to a given range and reduced recoil should allow for more snap shots to hit fleeting targets.

            There’s also the side benefits of encasing lead free projectiles to prevent feed ramp destruction, generally lighter wear on guns, and better tumbling characteristics at range.

    • DIR911911 .

      that sounds pretty close to the original 5.56 m16a1 , 20 inch barrel at 3110 fps. . . . maybe it’s all the “improvements” over the years that are hindering it now.

      • Nominal MV of the M16A1 is 3,250 ft/s, though.

        It doesn’t take very long for the heavier 62gr bullet to catch up to 55gr pills like M193, either…

  • lostintranslation

    The Small Arms Defence Journal: THE FUTURE OF THE MILITARY ASSAULT RIFLE by Jim Schatz.
    17 April, 2015 · Features, V7N1, Volume 7

    “Current U.S. statistics reveal that 21% of small arms KIA’s and WIA’s in Afghanistan are from 7.62x54R caliber weapons. Imagery from Russian operations in the Crimea reveal conventional Russian infantry squads armed with up to four 7.62x54R rifles and light machines gun per squad. Insurgents in Syria, Iraq and Afghanistan are deploying more and more SVDs and PKMs and the newer PKP light machine guns as well as bolt-action rifles in calibers .300 Winchester, .300 WinMag and .338 Magnum. Do they know something we don’t?”

    As I read the TFB Article my impression was that it is easy to be selective with data and historical perspective.
    There are several books detailing the process of selection that occurred for 7.62×51 and they don’t make easy reading.

    I believe that 7.62×51 will continue to be re-introduced because the 5.56×45 has proven to be inadequate e.g. Germany, Italy, Turkey, Pakistan, India? I expect the response be; ‘these countries don’t count anyway.’
    This is the legacy of the intermediate calibre fiasco since the 1950’s.

    Perhaps; the advantages of something like; .264usa, or 6.5×47 might eventually win through.

    If the US wishes to continue to champion 5.56×45 that is, your prerogative.

    It’s worth considering that; being on the receiving end of over-match is probably quite unpleasant and ‘the enemy also gets a vote.’

    • I guess you are not the biggest fan of the 5.56mm caliber…

      Yes, I’ve read Schatz’s article, his powerpoint presentations through 2016, and other things he’s written. He is clearly behind the larger caliber infantry round concept, but he does not address many of the arguments I have made over the years. Like many in his camp, when it comes to weight, for example, if it is discussed at all, the answer seems to be “well, it will increase weight by 25% versus 5.56 e en with a high risk lightweight case configuration, but who cares because it’s more powerful!” The problem with this reasoning is that there’s quite a lot of evidence to suggest that trading reduced weight and recoil for power negatively affects the soldier’s combat effectiveness, to say nothing of the crisis of overburdened soldiers and Marines in our services. It is convenient for advocates of larger calibers to ignore studies like the paper Rifle Squad Armed with a Lightweight High-Velocity Rifle, but that doesn’t make them any less relevant. Any switch to a new caliber should not be done just on the back of rhetoric and feelings, but carefully measured study.

      I’ve also read the relevant sources on the development of 7.62 NATO, including the seminal volume on the topic, HWS III, which was just released. Indeed, the next installment of my research project will be on the development of the caliber, and for that I’ve also read many of the primary sources regarding the subject.

      Turkey and Pakistan never adopted 5.56 in the first place, the Indians couldn’t develop a small arm to save their lives, Italy and Germany both still use 5.56mm as standard and have shown no signs of changing. So… Yeah, I guess I reject your examples of militaries moving to 7.62, but not for the reasons you thought.

      (You failed to bring up perhaps the best example, New Zealand, who actually is replacing the Minimi with the Maximi.)

      I guess “overmatch” is the word all the cool kids are using these days to mean “outrange”, and the arguments against that idea are the same as they have always been. The modern military is a combined arms force, equipped with mortars, artillery, aircraft, and other long range assets. Therefore, before one waxes poetic the ballad of poor Private Tommy whose M4 Carbine is outgunned by the Pashtuns, it’s worth considering whether a change in doctrine or something else might allow the services to better utilize the assets they already have.

      The thing about this argument is that the enemy will – if he’s competent – always try to attack your weaknesses and avoid your strengths. Different small arms concepts have different strengths and weaknesses; one example being that a switch to something like the .264 USA would almost certainly result in giving up anything like effective fully automatic fire on the individual level, while coming with penalties in ammunition weight and ease of training (try asking the NATO member states what happened to their qual scores after they switched to 5.56!). Who’s to say the Pashtuns (or if not them, the next guy) won’t just adopt new tactics to counter THOSE weaknesses?

      • lostintranslation

        Thanks for your detailed reply.

        I was most interested by your comment: “ I’ve also read the relevant sources on the development of 7.62 NATO, including the seminal volume on the topic, HWS III, which was just released.”

        I was expecting you to quote:
        The Great Rifle Controversy.
        Search For The Ultimate Infantry Weapon From World War II Through Vietnam and Beyond.
        Author: Edward Clinton Ezell (Curator, Division of Armed Forces History, National Museum of American History, Smithsonian Institution.)
        Forward by Eugene M. Stoner.
        Stackpole Books.

        I believe that Edward Clinton Ezell and Eugene Stoner were recognised, generally, as reasonably reputable authorities. Unfortunately; I’m not sure if they would stand shoulder to shoulder with the Author of your; ‘seminal volume.’

        I was also a tad disappointed that you resorted to: “I guess “overmatch” is the word all the cool kids are using these days to mean “outrange.””

        I think that brought the discussion to a convenient end.

  • iowaclass

    I really hope that these series on gun and ammo tech get put together in an e-book. I would buy it.

  • Kivaari

    Maybe it would not fit into this series but the Remington Bench rest cases loaded with bullets of 5.5 to 7.5mm seems to be a candidate loaded area. The 6.5x38mm grendel is nothing more than the 7mm BR case sized to 6.5mm. We have 6mm BR, 7mm BR and what amounts to the .308×1.5 inch in the 7.62x38mm (37/38mm = 1.5 inches). Although I have no need to be convinced that the 5.56x45mm is the proper cartridge for our armed forces. It has worked quite well now for 50 years and seems to have the proper balance of controllability, power and range that only the use of heavy bullets has enhanced, those cartridges built on the 1.5 inch BR case replicates much of the testing done in the 1950s. Nothing is new.

    • Erm, the 6.5 Grendel is based on the 6mm PPC case, not the 7mm BR case.

      • Kivaari

        You are correct. The BR is more like the .280 using the .476 diameter rim. The .308 x 1.5 was a spurt of effort in my youth where people were converting M1 Carbines. The Grendel is a more practical diameter for self loaders. Back to my old time thinking, I remember when I promoted the 6.5×52 with a spitzer bullet as being a better round than the 7.62mm NATO. that was before I realized how impressive the 5.56x45mm really was. It took my shooting thousnands of rounds over quite varied ranges and time to understand how good it was. It really helped to have been issued an M16A1 and seeing how full auto recoil and the M16 design were exceptionally well thought out. WE young men in the 60s really knew that big rifles were “really” needed, since that is all we had ever used. If it wasn’t a surplus rifle with cheap surplus ammunition we had little experience with them. Time allows us to play around with new stuff and finally see some credible reports on things that were covered superficially so many years ago.
        Now tha same goes for building rounds on the PPC case in each bore diameter. Just to show where that magic bore size IS.

        • mig1nc

          Hmm… 7mmBR looks similar to 7mm-08 Remington Managed Recoil. 2360 fps from a 24″ barrel. People are building super-light AR-10 platforms now, so that might be an interesting option.

          • Kivaari

            It seems that a VLD bullet in each caliber could loaded without crowding powder space. The 6mm BR seems like a great idea as well.

  • Fox Hunter

    so it was not very intermediate after all, too bad.

    • Yeah, at least not very intermediate-y and high performance at the same time.

    • ostiariusalpha

      There are human beings that can fire an M14 on full auto without being on the edge of losing control of their brace, just not enough to justify having a select fire 7.62x51mm service rifle. In the same way, there are limitations on the number of soldiers that have the strength and weight to manage the .280/30 in a select fire small arm. If your 6’5″ and a fit 210 lbs, then the .280 Brit is as “intermediate” a cartridge as you could want, but the majority of more moderately built soldiers will struggle to tame the round.

  • gunsandrockets

    Interesting cartridge. Seems very similar to 6.5mm Grendel except for its narrower bullet.

    If the question is improved close range lethality while hosing down the enemy with full auto fire with an M16, you probably can’t do much better than the M193 5.56mm cartridge you used in Vietnam. Larger calibers like the 6mm AR would sacrifice magazine capacity and full auto accuracy.

    That’s not to say other cartridges wouldn’t be superior to the 5.56mm in slightly different applications, such as with a shorter barrel, longer range fire, semi-auto fire, etc.

    The 6.5mm Grendel with 120 grain bullet is an interestingly close match to the .243 Winchester with 100 grain bullet, in recoil and the range to which 1000 fpe is delivered, yet still fit within the size of an M4 carbine.

    But as long as we are imagining ideal new cartridges for the AR, I like the old 6mm-222 cartridge with an 85 grain SP bullet.

    • The irony is that almost anything with the same head diameter (especially if it has a shorter case) as the 5.56mm is a no-go for military applications, because of the kersplode problem.

  • 6mm AR is a very interesting cartridge, and very well designed from a ballistic perspective. However, as a retrofit for the military M4 and M16 platforms, it is a no-go as the bolt thrust is too high.

    Fortunately, projectile technology has improved considerably since Vietnam, and modern M855A1 and Mk. 318 rounds more consistently than their predecessors deliver the excellent fragmentation effects that these small calibers have become known for.

  • idahoguy101

    If only the U.S. Army had adopted the 7mm Mauser. Or the 276 Pederson. Or the 7mm British. Or the 6mm SAW.

  • Jackson Andrew Lewis

    Much of the negatives of the round come from to many independant developments rather than collaboration….. the others come from capabilities the round does not have that were proven…. useless to say it in the nicest way……..
    Balistics of the round have influenced the wanted changed and moves away from 556 as well.