Do You Know Your HK’s Parents?

During this holiday season, perhaps you would like to take a break from visiting with your spouse’s parents  – so how about getting to know your rifle’s parents?

For a long time, the whole line of long guns made by H&K was all based around a single concept: roller-delayed blowback (sometimes erroneously called roller locked). The H&K 91 battle rifle used it, as did the 93, 94, 21, 33, 41, PSG-1, and MP-5 (and all the variants of them). Pretty impressive, really, that they were able to create such a wide array of guns from SMG to sniper rifle all based on the same basic principle.

So how does it work? The bolt in any of these weapons has a pair of rollers on the left and right sides, which push out into semicircular recesses in the barrel extension when in battery and ready to fire. This is a very effective way to build an gun, because it is cheap and simple to make precise rollers, and the semicircular recesses to match them are also easy to make. You need only push a solid block between the rollers to prevent them from retreating back into the bolt, and your gun is securely locked. The German MG-42 of WWII fame used this system to great effect, and it is on the shoulders of this giant that our H&K genealogy begins.

In June 1943 the R&D division of Mauser, under the direction of a man named Ott von Lossnitzer, decided to pursue the goal of using a roller-locking system like the MG42 in a Gewehr 43 rifle. The G43 used an expensive and somewhat fragile Kjellman-style flap locking system, and Mauser was looking for a way to build a similar rifle less expensively. By December of 1943 they had completed a test model of the converted G43 (which was designated the Gerät 03), and were putting it through a 5000-round endurance trial. It’s important to note that this rifle was a fully locked design, using a gas piston to unlock, while the H&K we all know today is a delayed blowback, with no gas system.

Gerät 03 roller-locked 8mm rifle

Gerät 03 roller-locked testbed 8mm rifle

Now we come to the critical development. One of the engineers working on the Gerät 03 – a man by the name of Dr. Karl Maier – noticed something unusual during firing. When the bolt on the Gerät 03 slammed forward into the barrel extension upon loading a new round, it would bounce slightly open again before settling down into the intended locked position. It was possible for the gun to be fired in the middle of this bounce, and when this happened the bolt would open much faster than the rifle’s gas piston was supposed to make it.

Roller locked system diagram

Gerät 03 diagram from Karl Maier’s notes. Note that the rollers rest on parallel surfaces, so no amount of force pushing back on the bolt can cause it to unlock.

The block used to push out the rollers had the firing pin at its tip, and an angled wedge to smoothly move the rollers. What Maier realized was happening during these out-of-spec firings was that the rollers were resting on the angled sides of the wedge when discharged, instead of on the main parallel sides of the block. As a result, the force pushing back on the bolt would slide the rollers in by itself, without and input from the piston needed. This sequence of events kept rolling around in Maier’s head while he worked, and by the middle of January 1944 he had conceptualized a brand new action, which would be simple and cheaper still than the roller lock.


Diagram of StG-45(M) locking system from von Lossitzer's notebook

Diagram of StG-45(M) locking system from von Lossitzer’s notebook. Note here that the rollers rest on angled surfaces, so pushing on the bolt will cause it to unlock.

Maier’s idea was to carefully calculate the angle of the wedge in the system, and get rid of the gas piston. By using the basic principle of a wedge, he would take the recoil force pushing back on the bolt during firing and split it into two components. Some of the force would push out into the receiver and center wedge, and some would continue to push backwards. By using the right angle, he could reduce the rearward force to just the right amount of force to open the bolt only after the bullet had left the muzzle and pressure in the barrel had dropped to a safe level. This is the principle used in simple blowback submachine guns and pistols, but in those guns the timing is controlled by changing the weight of the bolt. Maier’s idea was to redirect the force pushing on the bolt, and thus achieve the same result without adding a lot of weight.

Gerät 06H, aka StG-45(M) reproduction (photo by Oleg Volk)

Gerät 06H, aka StG-45(M) reproduction (photo by Oleg Volk)

Mauser subsequently build a rifle in 8mm Kurz (7.92x33mm) using this roller-delayed blowback system – the first of its kind. The rifle was called the Gerät 06H, and it was presented in December 1944 to the German military for evaluation. It was very well received, being significantly cheaper and faster to manufacture than the StG-44 rifle, and just as reliable and effective in use. The design was given the designation StG-45(M) (M for Mauser, as other companies were also competing to design the StG-44’s replacement) and an order of 30 guns was placed for further trials.

The parts for those 30 rifles were manufactured, but before they could be assembled into complete guns the Mauser factory was evacuated. Allied forces were on the verge of overrunning the town of Oberndorf, and the Nazis didn’t want the experimental new arms under development there (including the StG-45(M)) to be captured. Of course, the was would be over within weeks and everybody knew it, so the evacuation didn’t really accomplish anything.

In the aftermath of the war, there was a great flowering of interest in intermediate cartridges like the 8mm Kurz as well as the “assault rifle” concept among the Allied powers. The Mauser facilities at Oberndorf were in the French occupation zone, and many former Mauser engineers were put to work by the French developing small arms for an experimental new 7.65x35mm short cartridge. The first result of this work was a carbine designed by Ludwig Vorgrimler which was functionally identical to the StG-45(M). Called the CEAM (Centre d’Etudes et d’Armement de Mulhouse, a research division of the French Châtellerault arsenal) Model I/1, the first prototype was test fired in July 1948. A second design from another former Mauser engineer (Theodor Löffler) was ready in September 1948, and was also effectively a copy of the StG-45(M).

Vorgrimler Model 1 rifle designed for CEAM  (photo from "Full Circle" by R. Blake Stevens)

Vorgrimler Model 1 rifle designed for CEAM (photo from “Full Circle” by R. Blake Stevens)

Of the two designs, Löffler’s was preferred. While Vorgrimler continued to work on the program, Löffler’s design was revised several times into what was eventually designated the Model 50/1. This rifle retained the roller-delayed blowback system from the StG-45(M), but was chambered for the US .30 Carbine cartridge. It also included several more design elements which we will recognize on the HK-91, including an integral folding bipod, a rear sight located at the back end of the receiver (instead of over the chamber as with the StG), and a charging handle located forward and above the barrel.

CEAM Model 50/B serial number 6 (photo from "Full Circle" by R. Blake Stevens)

CEAM Model 50/B serial number 6 (photo from “Full Circle” by R. Blake Stevens)

We are getting closer to the H&K 91, but we aren’t quite there yet. In September 1950, Vorgrimler left CEAM and French employment, because of the general preference for Löffler’s rifle over his own, and because he simply wasn’t happy in France. He moved to Spain, where he was to be employed by the Centro de Estudios Technicales de Materials Especiales (Center for Technical Studies of Special Materials) or CETME – a name which should be familiar to HK91 owners.

Ludwig Vorgrimler (photo from "Full Circle" by R. Blake Stevens)

Ludwig Vorgrimler, circa 1950 (photo from “Full Circle” by R. Blake Stevens)

The Spanish government was also looking for a new rifle, but they wanted a larger full-power cartridge. When Vorgrimler arrived the project had already been underway for 9 months, and the rifle being built was a flap-locked design like the wartime G43. Fighting a lot of skepticism, Vorgrimler managed to get permission to design his own rifle – a roller-delayed gun based on the StG-45(M) and CEAM 50/1 – in parallel. The first prototype (called the CETME Modelo 2) was ready for firing in June 1951, and it made a big impression on the Spanish military. The first CETME rifle was dropped in favor of Vorgrimler’s system, and it was put into production. It is worth noting here that this early CETME rifle was chambered for an interesting 7.92x41mm (yep, 8mm by 41, not 51) cartridge with a very long 100-grain bullet. This interesting ballistic choice allowed the rifle to have a maximum effective range of 1000m while still having a relatively light recoil. Despite having some very interesting potential, this cartridge would be left behind in the wake of NATO standardization on 7.62x51mm.

CETME Modelo 2, designed by Ludwig Vorgrimler using the original StG-45(M) mechanism. Note the curved magazine for the early 7.92x41mm cartridge

CETME Modelo 2, designed by Ludwig Vorgrimler using the original StG-45(M) mechanism. Note the curved magazine for the early 7.92x41mm cartridge

Now, we have one last link in the chain – from CETME to H&K. How did that happen? Well, the German armed forces (what little they were allowed to have at that time) expressed an interest in the CETME rifle, and so the Spanish sent over a delegation to discuss production in Germany. Naturally, they went to the Mauser company – the birthplace of the design and a world-renowned arms company. Mauser management, in a stupendous failure of judgement, laughed the Spanish delegation out of the office.

Left unexpectedly out in the cold, the CETME team called up another manufacturing company located in Oberndorf, which happened to be a fledgling startup called Heckler & Koch. It had been founded in 1948 in by two ex-Mauser employees, and for several years was based in Heckler’s own home. By 1954 when the CETME connection was made, H&K was making sewing machine parts, machine tool parts, and dies and fixtures for other companies. The relationship with CETME would become its great opportunity, and allow it to grow into the armaments giant it is today.

Ian McCollum

Ian McCollum lives in Arizona, where he spends his time searching out rare, unusual, and experimental firearms for his daily blog at His shooting background is in bullseye pistol, and before becoming a full-time gun writer he worked in the solar power industry.


  • Graham2

    Even though I’m pretty well up on this, it’s really nice to have read again thanks.

    I guess Mauser didn’t like an ex-employee coming back with such a neat idea, their loss! It’s a bit like the guy who didn’t sign The Beatles when they first started out.

    Happy New Year everyone!

    • Burst

      HK, true to its origins, would ignore an opportunity to buy Glock years later.

  • Harald Hansen

    Nice overview, thanks! I’ve spent years lugging around H&K hardware in the Norwegian armed forces, so this is interesting reading.

  • Mike P.

    Stories like this are why I subscribe to TFB.

  • snmp

    The Roller Lock system is From the Patent n° US2089671 of Jully, 8th 1933 by Edward Stecke for Panstwowe Wytworine Uzbrojenia (Polish National Weapon Factory).

    Take a look in the patent digram

    When the German (Mauser) Rework the MG34 for masse production they add the Roller Lock in the MG42

  • ZeCatnip

    Great article. I really can’t praise it enough. Thank you.

  • AZRon

    I would like to add that H&K’s excellent P9s pistol also had a roller-delayed action.

  • El Duderino

    HK has a reputation for overengineering everything, but the roller delayed blowback weapons are as simple as can be. Anyone who has taken apart a G3 pattern rifle can attest to that. As simple as they are to make I’m surprised there aren’t companies designing new guns using the system, it seems like everything is gas operated these days.

    CZ-52 is my other favorite “roller” gun.

    • SAPH

      You’re spot on there. The local anti poaching unit uses a mix of FALs ,G3A3s, mini 14 and NAE AR15. G3 and FAL are the most popular. FAL because of its accuracy and range and the G3 because its similar to the FN but lighter and easier to clean. but the furniture on the G3 is crappy

      • Burst

        The slim G3 forends overheat, and the collapsable stock is an ergonomic sin, but the buffer stock and bipod forearm are rather nice for a combat rifle.

        And perched somewhere high above on a seraphic cloud, are the PSG furnishings.

    • Esh325

      Gas operation is more suitable I suppose.

    • kirk

      Roller-based delayed blowback weapons appear to be simpler to build, but the reality is that they are not. The only reason that H&K successfully managed to pull that off was via the usual intense Germanic attention to precision and detail. Everyone else who’s tried it eventually gave up and went with gas-operated weapons because the delayed blowback roller weapons are uneconomical to manufacture without that Teutonic anal retentiveness.

      This becomes particularly clear when you look at the 5.56mm variants. These weapons are very difficult and expensive to manufacture consistently, due to the pressure characteristics of the cartridge. Every country that tried, whether it was Spain or Thailand, eventually foundered on that factor. Once H&K withdrew its technical support, most licensed production in that caliber simply ceased, as the rejection rate for flawed parts went past the point where manufacture was affordable. As the skilled craftsmen who made serial production of the H&K weapons in Germany have retired, so too has production of those weapons become unaffordable. Which would be why, in large part, the reason H&K doesn’t build them anymore, either.

      Design is one thing. Being able to build that design affordably, and in sufficient numbers, is another thing entirely. Witness the US experience, where they chose the M14 partially because they were told by Springfield Arsenal that it could be produced on old M1 machinery. It wasn’t until TRW took over, and built entirely new production lines, that the M14 really became a mass-production item. Both the Springfield Arsenal and Winchester had experienced nightmarish production problems with the old tooling they’d adapted, never really managing to make it work.

      • Esh325

        Good post. The Roller delayed blowback of the Gerat-06/CETME was a sound and economical idea when it used lower powered cartridges like the 7.92×33, but when they had to adopt it to fire more powerful catridges like the 7.62×51, they had to use higher quality more costly steel and there were a number of problems that were never truly solved even with the G3.

  • Kosme

    Ian I watch all your vids in youtube, great channel, full of information.

  • schizuki

    More of these kinds of articles, please!

  • Awesome article, many thanks from Germany!

  • I think that Germans constructors ,engineers and precise and responsible workers have been producing best armanent in the whole World.They are systematic,and persistent in achieving good goals acording well prepared constuctions ,drawings ,calculationsb and after all of these important segments of production of armanent,work out in details each piece of machine-gun,gun ,revolver or heavy mashine -gun,and after all assembly that in good shaped unit which is practical and safe and purposefull for combat use of armanent.Except these things ,organisation of work is crucial and very important factor . In all together aspects, Germans at military-police industry for me,personally are the best.

  • AZRon

    Upon a re-read, I found something that doesn’t make sense to me.

    Unless I’m missing something, an 8mm diameter bullet that weighed only 100 grains would in fact be very short.

    • Ian McCollum

      The missing element is that the bullets weren’t made of lead. I think it was aluminum, but I’d have to check to be sure.

      • AZRon

        Not only does that make sense, it makes it even more interesting. I never even considered a different projectile material.

        Thank you for the follow-up.

  • G

    The German word Gerät means appliance, device or tool in English:

    As far as I know the G in initialisms such as G43, StG44 and MG42 stands for Gewehr (or rifle in English):

  • gallan

    Glock too wasn’t a firearms company that just rolled with the same design for decades.

  • W

    “It is worth noting here that this early CETME rifle was chambered for an interesting 7.92x41mm (yep, 8mm by 41, not 51) cartridge with a very long 100-grain bullet. This interesting ballistic choice allowed the rifle to have a maximum effective range of 1000m while still having a relatively light recoil. Despite having some very interesting potential, this cartridge would be left behind in the wake of NATO standardization on 7.62x51mm.”

    I didnt know that there was a smaller variant of the 7.92 that was bigger than the kurz! perhaps it was another true intermediate cartridge that became a victim of forced 7.62 NATO-ization.

    The more I study history, the more I develop my love-hate relationship with 7.62 and how the world of infantry small arms cartridges could have been so much more…

    • There’s a photo of the 7.92×40 CETME round about a third of the way down this article:

      The long, finely-pointed bullet had good aerodynamics despite being very light (the core was variously plastic or aluminium in the CETME developments).

      • Lal

        What twist rate did it have?

  • Zapp Brannigan

    The roller locking in the MG-42 operates differently from the delayed roller bolt in the G3 rifles. The MG-42 operates by short recoil; the barrel and bolt remain locked together for a short period as both move rearward. In the G3 rifle the barrel is fixed; it’s delayed blowback.

  • Mike Knox

    I was always perplexed as to why the Germans put wheels in guns..

  • jeff

    any way to get a copy of those design notes?

    • jeff

      I’m referring to the Great 03 notes by Karl Maier.

      • jeff

        Gerat* darn spell check lol