HK’s Other 4.6: the HK36 in 4.6 x 36

HK LogoAround 1970, Heckler & Koch was doing well, but their restless engineers were thinking: what’s next? One thing we learn from history is that no weapons system lasts forever, and there was maybe one more go-around in the company’s present line of roller-locked weapons, trading some militaries’ 7.62 NATO weapons for 5.56 NATO ones. But what could offer stingy weapons procurers enough reason to stop sitting on their wallets?

HK 4.6 x 36mm, made 1971. For sale here. It seems likely that there was only one lot.

HK 4.6 x 36mm, made 1971. For sale here. It seems possible that there was only one lot each of the “soft core” (lead, this) and “hard core” (tungsten carbide) FMJ.

The company explored many ideas, in two major strains. One is now well-known: caseless ammunition with a radically new action and new modes of fire, which became the G11 through many, many series of tests and evaluations in the 1970s and 1980s. The second was, perhaps, meant as a technical backstop if the G11, a technical stretch, proved infeasible. It became the HK36 — not the G36, the technical backstop HK had to create after the G11 failed, but the very obscure G36. The rifle existed in, perhaps, three prototypes. It used a unique 4.6 x 36mm intermediate cartridge.

HK 36 factory photo, as published in Full Circle.

HK 36 factory photo, as published in Full Circle. This is the configuration we call Prototype 3.

The Big Ideas: Weight and Spoonery

When we referred to this as the “other” 4.6, we’re referring, of course, to the fact that this is not 4.6 x 30 HK round used in the familiar (at least, in appearance) MP7 series widely used by US and foreign special operations forces. The 4.6 x 30 is the latest of HK’s many attempts to make an even smaller caliber round, but it was aimed at a different objective: the short-range SOF and LE submachine gun, making most shots inside 100 meters; it has very light bullets (31-40 grains for warshots) and is a hair over half the weight of 9×19 or 5.56×25 ammo, allowing a reduction in operator burden (or an increase in ammo load, naturally).

The 4.6 x 36 was developed in the 1960s to meet a different requirement entirely: that of a normal assault rifle intermediate cartridge, with engagement ranges mostly inside 300 meters. Two ideas drove the 4.6 x 36: reducing ammunition and system weight for a given effect, arguably the longest-standing trend in firearms design, and increasing terminal effect in the intended target, to wit, enemy homo sapiens. The first objective drove the reduction in caliber and length. To get to acceptable lethality, higher chamber pressures (51,200 psi CUP) were accepted, but the light projectiles (42 grain hard core/54 grain softcore) didn’t reach outlandish velocities (2,600-2,800 fps). It required a fast barrel twist to stabilize the light projectiles; 1 turn in 6.3″ was selected. HK claimed the round shot flat, allowing it to print to point of aim from 0 to 300 meters without any need for range compensation by the shooter or the sight.

The “spoonery” of the subtitle refers to an invention of Dr Gunther Voss of CETME, which remained in symbiosis with HK itself at least at the time he applied for German and US patents in 1964 and 65 (his US Patent, 3,357,357, was granted in 1967).

Voss Loffelspitz US3357357-0

…to provide a rifle bullet wherein the tip of the bullet is of an asymmetric shape. When this bullet strikes the target, forces are generated which accelerate the bulet inclination.

It is stil another object of the present invention to provide a rifle bullet wherein the turning moment produced by the inclination accelerating forces increases and the bullet inclination is produced more rapidly when the distance between the bullet center of gravity and the bullet tip is greater. It is possible to increase the effect produced by the bullet tip asymmetry through the backward displacement of the bullet center of gravity.

The CG change could be produced by a dual-material cored bullet (later Russian rounds would take this approach, without using Voss’s tip).

Voss 4.6 x 36 Löffelspitz (l.) with 5.56 x 45 for comparison.

Voss 4.6 x 36 Löffelspitz (l.) with 5.56 x 45 for comparison.

Voss further believed that by increasing terminal velocity with the subtly asymmetric bullet tip he called the Löffelspitz or “spoon tip,” he could reduce caliber without losing lethality, and without having to “underspin” the bullet, which was widely understood to be Armalite’s approach to small caliber lethality.

In addition to the effective range increase, a bullet with these characteristics offers the advantage of the possibility of reducing its caliber without decreasing the detaining power obtained with the calibers used until now.

“Detaining power” is a euphemism used throughout the patent application. But clearly, the one biggest Big Idea in the HK36 was this ammunition.

The Three Known Prototypes or Versions

It is possible that some of these are actually the same rifle before and after rework. The fairly comprehensive (to its date) HK reference The Gray Room does not include a picture of an HK 36, suggesting that this may not have been preserved by the firm (or it may not be in display condition). Full Circle only includes handout publicity pictures.

The receiver of the rifle is very slender and short and, while surviving weight figures (6.3 lb empty) generated by marketing personnel based on prototypes are hard to reconcile with real in-service weights, it should have been much lighter than other HK rifles and more competitive with AR-15 based contemporaries.

Prototype 1 had a very conventional HK roller-lock styled receiver and magazine well, and very conventional HK (as far back as CETME) drum sight. It showed a relatively early plastic HK lower marked 0-1-30 and had an unusual sliding buttstock, clearly inspired by the Colt CAR-15, even though the HK36 did not require a buffer tube.

hk36 prototype 1

 

Prototype 2 also had a fixed magazine well, but the drum sight had been replaced by an, also Colt- or Armalite-inspired, carrying handle/sight mount. A reflex sight is contained within the after third of this sight, but we’ve never seen pictures of it, or of its reticle; we do note that apart from Prototype 1 (above), all HK 36 photos appear to be innocent of any foresight or any provision for iron sights. This image was featured in the 1975 Jane’s Infantry Weapons edited by FWA Hobart. Hobart reproduced a factory brochure for the rifle inside the book. He also, at the same time, featured this firearm in an article in National Defense, the magazine of the (then) American Defense Preparedness Association (which was earlier the Ordnance Association, and would later be the National Defense Industrial Association). By this time, possibly unknown to Hobart, the HK 36 was destined for the back burner as the caseless project was beginning to look feasible.

hk36 prototype 2

That picture doesn’t really do the sight-tower justice. It would be preserved in the next prototype and we’ll see it from some more angles.

Prototype 3 took another turn in the direction of space age looks with a fixed stock with a high center so that the recoil thrustline is barely offset from the stock centerline. This would have the  effect of reducing muzzle rise in high-rate fire, including auto- or burst-mode fire.

HK36b

The selector now has four positions: 0, 1, 25, and 3, for a three-shot burst. This appears to have been a burst at normal cyclic rate.

The unusual magwell appears also to be a little bit inspired by Armalite concepts: a disposable waffle-reinforced magazine insert made of aluminum.

hk36mag

Changing a magazine was a Heath Robinson task on the HK 36; it appears from surviving photos that you have to move the mag well latch to the rear which would let the spring-loaded side door open and then you could insert the 25-Round magazine insert into the well and press the side door closed. At this point you could resume fire.

It may have been even more complicated than that. This is how Major Hobart explained it in the National Defense article (via Full Circle, p. 346):

The magazine is charged as follows:

At the bottom of each side is a milled button attached to a spring-loaded chain carried inside the magazine. When the buttons are pulled down, the chain is extended and held out. This pulls down the magazine platform and compresses the magazine spring. The rear of the magazine is open, and the 30-round box is placed on top of the followers. A further pull on the chain releases the holding catch.

The magazine platform rises under the cartridges and passes inside the containing box. The chain is taken up into the magazine. The first round is now in position for loading, and when the bolt comes forward the top cartridge is fed into the chamber. The magazine is sealed against the entry of dirt, snow, etc. As subsequent rounds are fired, the magazine spring drives the follower farther up inside the ammunition box. When the last round is fired, the bolt is held open. When the chain is pulled down, the empty box is ejected, the magazine spring is fully compressed, and the platform is pulled down to allow the next ammunition pack to be inserted.

(This is what happens when you ask a room full of guys whose names terminate in Dipl. Ing. to simplify something). HK claimed that this would “reduce weight and cost.”

It’s unfair to judge the magazine system based only on images and descriptions, but the temptation to pass judgment is strong. In any event, it is not the only ergonomic question mark with these firearms. The usual HK selector switch seems to call for the usual double-jointed thumb, especially on the burst setting; also, a stock weld of any type looks practically impossible, whether you’re using the fixed or sliding stock versions. (In true HK roller-lock fashion, they’re easily interchangeable. HK was modular before modular was cool).

The close-up of Prototype 3 shows the unusual shape of the forward carrying-handle pillars, and the only reason we can think that they’re bowed out like that is to keep them out of the field of view of the mysterious reflex sight. At around this time, HK was working with Hensoldt on a reflex sight for the G11; this might be the same sight.

Note that these “Prototype numbers” are not anything assigned by HK, but something that gun watchers have applied to these photos over the years as they’ve surfaced. We’re not aware of any picture showing more than one HK 36 in any one place at any one time, so it’s quite possible that there was only one prototype, and it went through several different reconstructions. It’s also possible that at least some of the weapons in the factory photos are actually mockups or dummies, and were never built as working firearms. The existence of quantities of the 4.6 X 36 ammunition argues for the existence of functioning prototypes.

What Happened to the HK36?

We know, in broad terms, what happened with the project. As the 70s wore on and the G11 project for a 4.9 mm (later 4.7 x 21) caseless Wundergewehr came together technically, the HK 36 and its unique 4.6 x 36 mm round vanished back into the swamps of, if not Mordor, at least Oberndorf. The G11 project was all-consuming, and it was this close to Bundeswehr adoption and standardization, having demonstrated a 100% pH improvement over the G3 rifle, when it was overcome by events. The Berlin Wall crumbled, and Germany entered the phase of Wiedervereinigung — the reunification of a nation divided in twain for almost 50 years. With the defense demands that resulted from this unexpected boon, including the challenges of merging two completely incompatible sets of armed services, it would have been irresponsible to sink great resources into rifle re-armament — so they kicked that can down the road, and stuck with the obsolescent G3.

The G11, which had already been rejected by the US Army when it cancelled the Advanced Combat Rifle procurement program in 1990, went into the lockers, too, and HK was briefly without a future in the infantry rifle market (right when worldwide Police/SOF enthusiasm for its submachine guns was running out of steam).

When HK found its future again, it wouldn’t be roller-locked or caseless. So one of the salient facts about the HK 36 is that it was, indeed, the last of a long line that began with the Mauser Werke StG 45. For that, as well as its innovative ammunition and concept, it deserves to be remembered.

We are aware that this post is far from comprehensive, but we think it tells the story of this rare experiment to the extent that it’s been made public. If there is a single thorough article on the HK 36 in the Intertubes somewhere, we did not find it. The best and most authoritative sources, based on factory information, are those 1975 Jane’s and National Defense articles, and three short pages in Full Circle, which reproduces much of the ND article’s content. 

20 thoughts on “HK’s Other 4.6: the HK36 in 4.6 x 36

  1. obsidian

    I stand slack jawed in amazement of that magazine!
    This was intended to be the Grunts standard weapon?
    Of all the ideas the spoon tip bullet is probably the best.
    A very informative article on a very obscure weapon.
    Thanks!

  2. arturo

    “The selector now has four positions: 0, 1, 25, and 3, for a three-shot burst.” Could you explain the 25? Also interesting article. That must have been some wicked spin on that projectile to compensate for the asymmetrical shape. Is there any info on what the two materials are? I am assuming lead and aluminium.

    1. Tim, '80s Mech Guy

      There is probably some magic number for how much of a chunk you can take off at a given twist. Some Australian over on utube has played with asymmetric bullits by grinding on .22lr rounds with predictable results. Then you have the issue of overspun light bullits which when pushed too fast disintegrate in flight like the .300blk fans are doing with the new Lehigh 78gn . It’s all about finding the sweet spot.

    2. Hognose Post author

      HK practice of the day was to number selector switch positions. The high number was the standard mag capacity, and indicated full auto. Even though the description says 30 rounds, every example of the “Prototype 2” configuration I’ve seen is marked 25. But I’ve only seen photographs, and HK has never really told the story of this also-ran design. I interpret the 25 instead of 30 to mean that the capacity of the inner-magazine was only 25 rounds.

      If you use numbers, you don’t need to remark safeties for every new language when you get a new customer!

      Note that later HK changed marking and the full-auto selector setting now has the mathematical symbol for “infinity.”

      Apologies for typos… been in travel mode all day and just catching up with no glasses on!

  3. Jim Scrummy

    I come here to be educated, and never leave disappointed in my time being well spent learning something new. Thank you!

  4. Kirk

    HK has some very good engineers, and had some excellent craftsmen working for them. What they lacked was anyone who knew how to make money as a businessman, or had the slightest amount of common sense in the arena of business and/or tactics. In contrast to the pre-war era, when the base-line elements of the German MG tactics were worked out, HK seems to have worked in isolation from the Bundeswehr as far as this project and the G11 went. I got the chance to sit down and talk weapons with a German exchange officer who was that rara avis, a firearms enthusiast, and he had some interesting things to say about the relationship they had with HK. Per his description, HK was a hell of a lot better at lobbying the people in Bonn then they were at producing what the Bundeswehr wanted or needed. There is a damn good reason the G11 was dropped like a hot potato as soon as the wall came down, and that’s because the Bundeswehr did not think the tech was ready for deployment, and was pissed as hell at the way HK was doing an end run around them to the people in Bonn. Which explains a lot about why they studiously looked the other way, twiddling thumbs while HK went tits up and was sold off to Royal Ordnance. If you look at the business news, the Bundeswehr didn’t do business with HK again until all the company leadership that was involved in forcing the G11 on them was retired or fired. Per the German Major I talked with, that was the “inside baseball” reason they let HK go bankrupt. Which makes sense–I always thought it strange that the Germans would so blithely allow their only major small arms producer to go out of business, watching it happen while they sat on their hands. HK apparently pissed a lot of people off, with all the shenanigans surrounding the G11. All those changes to specs thay enabled the project to “succeed” on paper were forced on the Bundeswehr, and they did not like it, one damn bit.

      1. Kirk

        The impression I got from this German officer, who’d been involved in portions of the G11 testing, it was more like the guys running HK at the time regarded the Bundeswehr as though they were a captive market, and every time the military brought up an issue, like “G11 cartridges are too fragile”, the HK bigwigs would go off to Bonn, talk to the politicians, and then the criteria would get changed. The biggest thing that was angering the officers, however, was the sheer arrogance and condescension they were getting from the HK people. They’d raise an issue, and then get a pat on the head and told that they just didn’t understand what a gamechanger caseless would be. He said that it felt that the objective of the program didn’t seem to be to get the best rifle for the Bundeswehr, but to make HK look good by building the first caseless weapon. He felt like the wall coming down was a huge blessing in disguise, because it gave them a politically OK solution to getting out from under the entire program. It’s worth noting that they’ve never tried resurrecting it, either. And, you’d think they would have, when they decided to replace the G3.

    1. Hognose Post author

      Jim Schatz (ex-HK USA) has an excellent presentation on why the caseless round is the round of the future not just now, but in the future, too…. He probably knew the G11 platform better than any other native English speaker. I believe that prez has been featured here before, but haven’t time to dig for it. I bet Jim’s comments would dovetail nicely with your BW friend’s.

      Polymer case gets you about 80% of the weight savings you can get with caseless, but what they don’t have is polymer obturation as good as brass… yet. We’ll probably see that long before caseless.

      1. LFMayor

        So that means that the case doesn’t hold the projectile long or tight enough to build enough pressure to cause the bullet base to swell into the lands?

        What happened to the revolver ammo that was polymer, I first saw that early 90’s but it was forgotten pretty quick like?

  5. S

    Amen Amen: another Very Good Article(TM) by WM. The spoonbill bullet was the biggest takeaway…..and I thought it would be inaccurate, but I guess the shock cone and the spin rate and short range wouldn’t make that such a big deal.

    Arturo, I think the “25” on “prototype 2” means that’s how many bullets are meant to come out per trigger pull…though that would make it seem as though they lost 5 rounds over “prototype 1”. Meh, leave the rock’n’roll to the MG’s, please, imho. If one really needs that much at once, then it’s better to make as many of them count, and spend less time monkeying with that (gag) reloading system.

    Off topic (still German, and almost gun): I gave in to temptation on an impulse buy…..an Umarex copy of the Mauser C96, in .177, CO2 powered (yay, warm it). For such an ugly classic it sure points well, and for a smoothbore gas toy launching round steel balls it’s no slouch at accuracy either. Just a little louder than I expected, so I’ll have to crank up the volume on some fillum when the need to make holes in paper comes upon me. Ok, it’s a toy for a big childish idiot, but it’s all metal and wood, and makes me want an original. As a boon, I could spray it black, glue on some large washers, and pretend I’m Han Solo (and yes, I would draw first).

  6. Tierlieb

    Quote: “(This is what happens when you ask a room full of guys whose names terminate in Dipl. Ing. to simplify something). HK claimed that this would “reduce weight and cost.””

    Or what might happen if you tell the Dipl. Ing. that they ought to build a system that might convert nicely to caseless ammo.

    P.S.: Unlike the American PhD, which goes after the name, the German Dr. and Dipl. Ing. go before the name. Or did, at least before the advent of the internet.

  7. DSM

    The magazine is sealed against the entry of dirt, snow, etc.

    …that is until the first time you open that little door to reload.

  8. emdfl

    The problem with the .38 polymer was that too often the projectiles didn’t jump out of the case when fired; rather they would tear the end of the case and cause cycling problem or ejection problems in the revolver. I suspect this may have been caused by the type of projectile used. It was a FMJ with a knurled lower end. That knurled end may have been catching on the soft case when fired.
    I have about 8K(?) rounds that I am breaking down (slowly) to salvage the projectiles and powder. I’m going to try reloading the cases that don’t tear with a lead wadcutter projectile and a light powder load.
    Also have some of the original 5.56 poly. I was told that it was pretty reliable as long as you didn’t go FA with it…

  9. obsidian

    I have noticed the 5.56 x 45 mm hunting rounds sold as soft points had lead that at times would deform into a spoon tip shape when loaded into a magazine.
    I wonder if that was a boon or bust for the lead tips of the rounds?

  10. Tam

    The magazine setup on the final variant is like a joke about German engineering come to life.

    Did you hear about the German anvil? It’s electrohydraulic and has fifteen moving parts.

    (Also a splendid example of a bit of gee-whiz engineering put into a gun by someone who is obviously not really a shooter.)

    1. Hognose Post author

      Like the Porsche 911: a triumph of dogged engineering over a foundation of that design.

      (This comment, which was dictated at the pool in the bright sun, has been corrected once indoors. I did not mean “dog at” engineering. That would be the French, as any other former Citroën owner can tell you).

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