L4: The Bren in 7.62mm NATO

When the British military transitioned form the .303 British cartridge to 7.62mm NATO in the 1950s, it replaced the Enfield rifles with the new L1A1 SLR (the FAL) but retained the Bren gun as a support weapon. The Bren was updated to use 7.62mm, in a process more complicated than most people would think. Ultimately, only a few thousand L4 series Brens were made, as they were rather quickly supplanted by the FN MAG as a belt-fed support weapon.

The four different patterns of L4 are:
L4A1 – the initial pattern, without magazine supports
L4A2 – the Bren MkIII in 7.62mm with magazine supports
L4A3 – the Bren MkII in 7.62mm with magazine supports
L4A4 – the A2 and A3 patterns with chrome-lined barrels


  1. Ironically, in converting the Bren to 7.62 x 51mm, the British Army essentially came full circle back to the original ZB26 in 7.9 x 57.

    Ballistically, 0.303in and 7.62 NATO are generally similar to each other. But pressure-wise, 7.62 is closer to 7.9 than it is to 0.303in, as the Indian Army found out in converting the SMLE and No. 4 to 7.62 NATO. This has in the past led to some surprises, not all of them pleasant ones.



    • “This has in the past led to some surprises, not all of them pleasant ones.”(C)

      Do You think it’s a matter of pressure?
      I have seen Chinese BRENs with cracks on the upper body.
      But I thought it was a chinas-steel question…

      • Keep in mind that the “Nationalist Chinese” 7.9 x 57 Brens were made in Canada. So I don’t think “Chinese steel” was the problem.

        A better guess would be that the shorter gas piston of the Bren compared to the ZB26 was originally intended to ensure reliable functioning with the lower-pressured 0.303in round.

        So you have a 7.9 x 57 design, modified to use 0.303in, then modified again to use 7.9 x 57 with no major “reversions” to the original setup.

        What was most likely happening was that the shorter gas piston assembly intended for 0.303in was delivering 7.9 x 57 gas efflux to the piston, meaning higher pressure there. This means higher piston and bolt velocity.

        That would likely crack the receivers pretty quickly in service.



        • The Mk8 loading of .303 was intended for machine gun use, its operating pressures are right up there with 7.92×57, and even 7.62×51.

          There is a difference in the internal area in the case head, so for the same pressure, the .470″ diameter case heads will give more backthrust than .303

          That actually becomes significant in things like bench rest, where the top performing case, the 6mm ppc, uses a head diameter very similar to the. 303, rather than the slightly larger. 470″ diameter.

          I don’t know where the steels that inglis used, came from.

          If it was America, the Americans allow a lot more phosphorus in their steels than most other places

          Also, being protected by Hamiltonian tariffs, the American steel makers usually held to a lot lower quality standards than steel makers who were exposed to more competition / a less cosy environment.

          Most ferrous alloys (including steels) have a brittle transition.

          They go from elastic to plastic


          Elastic to brittle failure

          The temperature at which the sudden change in behaviour happens depends upon a bunch (a veritable “fascie”) of factors

          The factors raising the temperature of the brittle transformation include increasing phosphorus, sulphur, chromium and vanadium, along with silicate (as stress concentrating starters for cracks).

          Heat treatment also plays a part with Bainite being particularly sensitive.

          What temperatures are we talking about?

          Things reached the point of undeniability in WWII, when a “liberty ship” snapped in half while moored in port.

          The disintegration of “liberty” ships could no longer be blamed on U boats.

          Attempts were made to blame the all welded, rather than riveted construction.


          It was crappy American steel, that went brittle at around 3° to 5°C – normal north Atlantic winter water temperatures.

          Its true that Americans didn’t/don’t have a monopoly on shite quality steel,

          the Northern Irish steel makers, using lateritic ores from the weathered tops of the Tertiary age basalt lava, have the big brittle fracture of the Titanic (in cold water), as lasting testimony to their shite steel making.

          But, it’s usually Americans, who’ll project their own nation’s crappy record for absolutely shite steel – onto everyone else

          A lot of China gets very cold in the winter…

          It’s typically -20°C from October through to March in inland Manchuria.

          In the absence of the intensive and rigorous investigations that eventually led to the identification of a brittle transition as the cause of the problems with the “liberty” ships

          Take your own guess as to the problem with the Chinese BrEns.

          Incidentally, all Martensitic Stainlesses (the stuff stainless actions and barrels get made from), have a brittle transition from about room temperature
          It doesn’t get really serious until much lower temperatures- but, be warned, whether you are in the colder parts of Eurasia or North America,Martensitic Stainless is not your friend.

          • “(…)I don’t know where the steels that inglis used, came from.

            If it was America, the Americans allow a lot more phosphorus in their steels than most other places(…)”
            I do not know for 100%, but considering that as https://wartimecanada.ca/document/world-war-ii/resource-industries/iron-and-steel claims
            [In 1945] Taken as a whole, to include both primary production and fabrication, the industry is the biggest in the country; it employs one twelfth of all people gain-fully employed, produces nearly one third by value of all products, owns almost a third of the productive facilities of the country. At the peak of war production (1943) it employed 435,000 persons out of the total 1,241,000 working in factories.
            they likely used own steel.

          • Thought provoking writeup. From what I remember from metallurgy, the ambient temperature is a decisive factor when comes to low temperature brittle failure. It is so easy to forget it when we talk about weapons.

          • Guess you never been to the US Midwest in the winter. That is where much of the US steel is/was made and most of it used. A temp of -20c, a mere -4f is no big deal nor any problem for anything made of steel that is of a good design. If there was a problem because of cold weather, it it the design of this MG.

            Also I’ve hunted full days when the high temp is -15F or -26C with rifles made of stainless steel.

            I think you have zero experience and very little knowledge of real world cold weather and steel use in it. Also, what would the Irish know about the use of steel in cold weather? It never even gets cold there.

  2. A Bren will always be a Bren, and a FAL will always be a FAL. The rest will be like aspirine against cancer ! The world comes back to gas pistons and to 7.62 !
    As i mentioned before, i hope to see one day an assault rifle with a 0.303 Bren mag.This caliber was dropping elephants in Africa once upon a time !

    • Check out the book Improvised Modified Firearms by J.David Truby and John Minnery. In the chapter on the Vietnam War, they show a photo of what they describe as an AK “clone” in 7.62 x 54R made from “parts of downed American aircraft”. (!)

      It’s actually an SVT-40 with a professionally-shortened barrel/gas piston assembly, a side-folding stock that was most likely made from seamless square-section steel tubing, a hand-carved wooden AK-type pistol grip, and a Bren 30-round magazine. Which should work perfectly adequately with 7.62 Mosin-Nagant M1891 ammunition, due to the similar dimensions and profiles of the cartridges.

      I don’t think it was a VC weapon. The workmanship is just too good. It looks more like some Army or Marine armorer’s weekend “hobby project”.

      It must have made a truly awe-inspiring racket on full-auto.



      • There was this religious sect in Vietnam that produced their own, I think maybe even fairly good firearms, maybe (in that time) on level with Darra (not Darra today)

        • That would be the Cao Dai, in Tay Ninh province, west of Saigon, not far from the infamous Cu Chi tunnel country.

          They barely tolerated the old Saigon regime but hated the VC with a passion.

          Still going strong, but appear to have been “persuaded” to stop making 1911 and Browning HP knock-offs.

          • Thanks for the reply. I hadn’t thought of that. Would make for a handy cartridge.

            Interesting gun there. The Chinese militia conversions and arms in general are always interesting. Maybe the twin machine gun was to make up for the Type 38s that were converted to single shots.(?)

        • It has been done by several people.

          Basic version involved running a 7.62 x 54R reamer into a .303 chamber and tinkering with the gas system.

          The cases come out with a weird “double shoulder” and magazine capacity is rather limited because of the larger diameter and different “taper” of the case. Of course, the bolt-face and extractor need to be “adjusted” as well.

    • Yes, they absolutely were–and were very popular according to what I have read. In fact, the 7.62 Bren was still in use with support units during the first Gulf War.

      • Britain’s SAS used .303 and 7.62 Nato L4 Bren guns for ‘firing on fixed lines’ in the Falklands.

        The Lithgow (Australia) L4s were still quite accurate, IME.

        And JBTWay IME ‘rim-jams’ with .303 ammo in Brens and in SMLEs is not common, at all. The bolt-stroke force even in SMLEs is sufficient.

        I’ve put a lot of rounds through a sporterised SMLE in .303/25 on feral pigs down here, and just never worried about it.

        I was Marksman/Coach qualified in my late 20s.

  3. I trained on one of these in the TA in 1980 . Reliable gun , accurate and a lot lighter than the GPMG. Remember we used a coin to change the gas setting after loosening the barrel . Seemingly this weapon was popular with the soecial forces deployed in the Oman action. Apparently ammunition economy was a major consideration in the desert.

  4. I ment, the mag below and the piston on top. As Bren had no feeding issues with the rim, it would be an interesting adventure. Maybe it will make the rimless,” an answer to a question never asked” ! Dropping elephants with the 0.303 is presented in the G&A annual of ’86.It’s not imagination.

    • Karamojo Bell used the 7X57mm Mauser for most of his African hunting, and since he had his horse shot out from under him by the same caliber…? .303 British for the same job isn’t as much of a reach as many would think.

      Hell, my stepdad had a story about going hunting for polar bear with an Inuit hunter, whose sole weapon was a really rickety Winchester lever-action of some indeterminate vintage that his grandfather had traded with a passing whaler for. It was chambered in what I think (stepdad was not a gun guy, and his description was not what mine would have been…) was probably .38-40 black powder. The rifle had to be stood on the muzzle and then hung off of the lever to get it open, and then kicked shut. Magazine didn’t work, so it was a single-shot. The cartridges were green with verdigris, and were apparently of the same vintage as the rifle–The original deal was for the rifle and a case of ammo, in return for five seals or something. The original hunter had passed the rifle on to his son, then grandson, with the original transaction having taken place in the 1880s.

      I might point out that precisely none of these details were known to my stepdad, who was at that point in his life a fairly recent immigrant to the US from the Balkans, and who’d had no real exposure to indigenous people or their lifestyle. He’d literally just gotten off the fishing boat in Alaska, made friends with the locals, and got invited out to go hunting with one. I wish I could do his storytelling about this some justice, but I can’t even begin to get the whole atmosphere right… Suffice to say, it was epic.

      About like his story about his first encounters with avocados in California, wherein he and some of his other Eastern European buddies thought that you were supposed to peel them and eat the seeds…

      They never could figure out why they were popular, or where the hell the green stuff in guacamole came from. It wasn’t until one of them got a Mexican girlfriend that any of that came to their attention, and that took a couple of years after immigrating here.

      • I can’t remember which of the writers about African hunting, used to quite happily use 6.5×54 mannlicher schonauer on elephant.

        There was also a craze for using .22 savage high power on lions and tigers.

        Taylor, writing shortly after WWII, noted that back when Bell etc were shooting, the elephants had no experience of getting shot at, and herds grazed out in the open.

        Carefully picked shots could be taken at comfortable distance, but, a gun bearer usually carried a heavier rifle along, incase the situation got more complicated.

        By Taylor’s time, elephants were wary, and didn’t expose themselves in the open in daylight, shots were taken at very close range in thick thorn scrub or full forest.

        The earlier 215 grain .303 loading had a fairly strong jacket. The mk6 215 grain loading, reduced the jacket thickness in order to increase the chances of bullet deformation – which is exactly the opposite of what you want for big heavy animals.

        That thinner Jacket is possibly the factual background to the oft repeated claims that 303 wounded a lot of game, while the same writers often make great play of the miraculous slaying powers of, say .30-06 150 grain loads

        I can’t remember the name of a Rhodesian game warden who usually used his FAL for elephant culling. He did have a big rifle there incase it was needed for following a wounded animal into dense scrub, but the need didn’t arise.

  5. I’m not sure it’s fair to say the 7.62 Bren was “supplanted” by the GPMG (FN MAG). Rather, they were used side by side at least as late as the Falklands War. I’m sure the soldiers who “yomped” from San Carlos to Port Stanley carrying the L4 were much happier than the poor guys who had to carry the GPMGs.

    • L4 Brens were also used by the Royal navy. I have seen photos from the Falklands war of them being used in the bridge wings of ships, including HMS Invincible, as last ditch anti-aircraft guns. Very last ditch.

      I think the last wartime use of the L4 Bren by Britain was in the 1991 Gulf War, when some units were still armed with the L1A1 SLR. When the crap L85A1 SA80 and the even crappier L86A1 LSW became ubiquitous, the L4 Bren disappeared. If I know the British government, they will have been destroyed. It’s just as well a few are in the USA.

  6. L4A4 Bren Guns appear to have also seen service in New Zealand. Development was by both Canada and UK separately with the gun adopted being a combination of the best of both according to a locally printed brochure? L4A4 was in limited Australian Army service appearing to be purchased much later than the UK introduction possibly due to M60 issues (guns worn out from Vietnam by the 1970’s) and poor performance of the L2A2 (updated version cancelled) with the Bren as a stopgap? Suggestions that the L4A4 had issues may be related to the use of L2A2 30 round magazines not working as well in the BREN. Co-incidentally the updated L2A2 was to only use 20 round magazines and fire from an open bolt by modification of the hold open device. No General Australian Naval service as far as I know as the navy used the L2A2 and limited use of the FNMAG in helicopters. Have not found how many L4A4 Bren’s purchased by Australia.

      • That’s interesting, I was under the impression (need to find the original reference) that the Australian L4A4 Bren’s where sourced from the UK. That is reinforced by civilian owned Australian L4A4 Bren’s I have sighted (Pre-96) being of UK manufacture. Do not know however if these where built from kits at lithgow, which is a possibility?

        • The number of L4A4 Bren’s that Australia purchased is quoted as 1100 with some additional stock of spares. There was to be an L4A7 Bren – Australian specific model, which did not eventuate? I have no knowledge of this maybe someone has? Lithgow SAF manufactured barrels and magazines as these where not covered by licence. The reason is – quoted as, that Enfield would not grant a licence to manufacture due to competition previously in regard to L1A1 Australian export sales undercutting Enfield?

          • Every L4 I ever saw, fired or repaired in Oz service was Brit built.

            As for Lithgow, they had “a plan” to do a conversion in the early 1950’d. There used to be a set of drawings in the Lithgow archive towers that were so early, the new cartridge was still referred to as the “Calibre .300” round; i.e., PRIOR to the official adoption by ANYBODY of the 7.62 NATO cartridge. As far as I know, if ANY trials /prototype guns were built, NONE survived. I vaguely recall that the plan was to initially use “leftover” breech blocks from Canadian 8 x 57 production for the Nationalist Chinese.

            The conversion is NOT for the faint-hearted as folks who have tried it will attest. The dimensions of the internals of the magazine well are critical. LOTS of .303 Bren bodies were turned to scrap in the process of “perfecting’ the mag well modifications. Part of the problem is the differences in feed lip design between the 8mm Bren mag and the L1A1 mag.

            Note also that South Africa did a bunch by themselves; using true FAL mags. (and only 20 rounders), with the dinky front “catch” stub.

            Anyone with trigger time on one of those?

  7. Spent the weekend at the Big Sandy MG shoot firing both a Mk 3 Bren in .303 and an L4A3 in 7.62. We never had a single malfunction in either gun, and with the exception of a few old cordite .303 rounds failing to fire, we had an amazing time !!!

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