Heckler & Koch’s Modular Machine Gun: the HK21E

In 1961, Heckler & Koch introduced a new light machine gun based on their roller-delayed blowback system as a companion piece to the G3/HK91 rifle. While the German military was quite happy with its MG3 machine guns, H&K expected that other, smaller nations adopting the G3 would be interested in a support weapon that worked the same way. They were not wrong, and the first adopter was Portugal, in 1968. By 1977, some 20,000 had been sold to more than 20 different nations.

In the early 1970s, a number of improvements were made (including a clubfoot stock and optics mounting points on the receiver) and the HK 21A model was introduced. Additional major improvements in the early 1980s created the HK 21E “export” model. This had a longer receiver, longer barrel, strengthened receiver, improved recoil buffer, and was fully modular, able to be assembled into a model HK11, 21, or 23 (that is, magazine fed 7.62mm and belt fed in either 5.56mm or 7.62mm). Today, the model has been replaced in HK catalogs by the new MG4 and MG5 machine guns, but licensed production of the HK 21 in Portugal and Mexico ensures that the guns will be around for many years to come.


  1. I’ve been waiting on a video about the HK-21, this is my favorite machine gun because of the modularity and how it’s based off the G3 Rifle. I showed my grandfather this video and he remembers shooting one of these guns back in the Navy Reserves.

    • Now I am really interested. What would NASA use machine guns for? Or was it a case of arming guards with them? Seems a bit overkill for me.

      • Probably some sort of security response team (SRT) at places like Kennedy Space Center. The SRTs respond if the initial response force is outnumbered or outgunned.

      • NASA has a very well equipped and reportedly well trained security force. Remember that it’s not just civilian space exploration, but a lot of secret and sensitive operations take place at their facilities. And no one takes international sabotage or terrorists lightly!

          • Yeah, and if you go any further than that and blackmail the higher-ups with the possibility of leaking sensitive information, you will “conveniently disappear” and then “reappear” as a car-crash victim. JUST KIDDING!

          • Got a few too many creepy as f sites like that around me

            It makes me wonder whether they were cold war missile sites or ongoing kiddy fiddling sites 😐

  2. Hmmm.. I wonder. You’ve got to keep a vigilant eye out for all the cannibalistic body fluid drinking deep state satanists lurking behind every bush.

  3. Interesting story.
    And the rifle is interesting.
    That’s just, I still do not understand why it never received distribution as LMG?
    Let’s say it’s clear with the German army. They didn’t need another machine gun, only less effective and more expensive.
    But what did not suit other countries, especially those already having G3 supplies? The adoption of such a machine gun would seem logical and consistent.

    Or was the structure itself so fragile or unreliable?..

    Let’s say that cooking a cartridge after 1000 shots and insufficient stability is probably not such a big problem. Moreover, by strengthening the receiver, the stability in automatic mode was slightly improved.
    Apparently, the main problem was with the service life.
    Having strengthened the receiver, they increased it to 60,000…
    But for a belt-fed machine gun, these are tears.
    Especially against the background of the price of a small aircraft.
    Let’s add here almost insurmountable difficulties with licensed manufacturing.
    As well as the dubious survivability of the belt drive…

    Everything is complicated and expensive to manufacture, and also capricious in operation.

    I think this is the answer.

    • Poorer countries buy guns when “bargains” present themselves. Which often meant a superpower would dump old guns on them for free to win their favor. Say I’ve already had the US or UK dump a thousand 7.62 NATO machine guns on me already, and I’m not at war. Those things will last forever. But I need rifles too, and H&K will sell to anybody. So I get the G3, but not the HK21. Slightly wealthier countries already bought their G3s and FN MAGs before the HK21.
      It would take a very smart ruler to realize that by buying the HK21, he could future-proof himself against future calibers.

  4. Matt
    I think the first country to have adopted the G3 based LMG is Burma in 1964, not Portugal in 1968. The official designation of the G3 is ‘BA 63’ while that of the LMG version is ‘BA 64’ but commonly referred to as the G4. The G4 was much lighter than the Bren could use only a 20 round magazine.

  5. A machine-gunner in Houston let me examine his HK-21. “Those Germans really know how to make a machine gun…!”

    Portugal was in the 1960s reconfiguring the entire armed forces for COIN in Guinea-Bissau, Angola, and Moçambique/Mozambique, having already lost Goa to India. The Fábrica Braço de Prata manufactured the German G3 with a West German technical package and advisement direct from Oberndorf. Initially, the JFK administration was hostile to Portugal’s intent to hang on to its African colonies, but the Estado Novo adroidtly exploited the value of the Azores bases to Nato, and found that while some Nato nations were revolted at the state’s “Guerra do Ultramar”–like the Netherlands, so no more AR-10s for the air force–West Germany was willing to assist. Eventually anti-communism and the value of resources in Angola, etc. got other powers interested too.

    The FBP-made HK21 had many teething troubles, and of course by 1968 there were MG3s as well as all the legacy antique MGs like the Madsen m/930-41, 8mm Breda m/938 (M37),”Dreyse” m/938 (MG13), MG-34 and MG-42, among others.

    I recall seeing an early photo of MPLA rebels in Angola with Soviet PPSh-41 SMGs and an old Schwarzlose water-cooled MMG on a tripod.

    I could see an HK version of the gun as a “22-E” able to use RPD 7.62x39mm drums and/or RPK magazines along with the HK32 rifle no one seemed interested in… Tough to market anything like that viably with Kalashnikovs, RPDs and RPKs presumably far, far cheaper, no?

  6. I’m trying to build a replica HK11EW. You will need Tokyo Marui G3 series parts. However, only the stock needs processing. It looks like it will be possible to cut the stock of PSG-1 and G3.

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