StG-45 Horn Prototypes

Herr Horn (I have seen his name given as both N.V. Horn and V.G. Horn; not sure which is correct) was an engineer working in the R&D department of Mauser at the end of WWII, and he designed one of the many different experimental last-ditch rifles that was conceived in the last years of the war. The requirements for these rifle designs were to use standard MkB-42/MP-43/MP-44/StG-44 magazines, weigh 4kg (8.8lb) or less, have a barrel the same length as an MkB-42 (413mm / 16.3 in), and to be select-fire with a cyclic rate of approximately 500 rpm. And, of course, they should be simpler and cheaper to produce than the standard sturmgewehr while maintaining it’s combat effectiveness. Initially the guns were required to be blowback operated, in the interest of simplifying production and design. Of course, this was problematic – the bolt required to safely contain 8mm Kurz without a locking system would take up a large percentage of the allowable overall weight.

Horn prototype sturmgewehr
Horn prototype sturmgewehr (photo courtesy Larry Vickers)

Some designers continued with the blowback system, most notably Barnitzke, with the Volkssturmgewehr Gustloff (aka VG1-5) and Maier with the Gerät 06H. Horn, however, decided to add a sort of gas system to delay the opening of the bolt.

Horn StG action diagram
Horn StG action diagram

Horn used a barrel fixed in a stamped sheet metal receiver, with a long bolt much like a pistol slide. Above the chamber was a small gas piston which was connected to a gas port just in front of the chamber. When the rifle was fired, gas pressure would immediately force the piston up and into a recess cut in the slide. The bolt was able to travel rearward only about 1mm before the piston engaged, and then the rearward pressure on the bolt had to fight against the angled surface of the piston engaging in the bolt. This was not a truly “locked” system, but rather one of gas delay, as the piston was intended only to counteract some of the chamber pressure and slow down the opening of the breech.

In early testing it was found that a free floating piston caused problems. If the rifle were manually charged while being pointed downward, gravity could pull the piston forward and cause a nasty double feed type of malfunction. This was addressed by adding a light spring to constantly push the piston downward. The spring force was not enough to have any adverse impact on the firing cycle, but it would counteract gravity.

Horn rifle piston in the unlocked position
Horn rifle piston in the unlocked position. Note the spring pushing the piston to the right. (photo from Johnston & Nelson’s “The World’s Assault Rifles)
Horn rifle piston in the locked position
Horn rifle piston in the locked position. Note that the return spring has been removed for this photo.

Another interesting element to take note of is that Horn extended the magazine supports in the front and back of the magwell as compared to the StG-44. These magazines when fully loaded were both heavy and long, and would bounce back and forth on firing, eventually wearing a crease in the front of the magazine where the magwell ended. This would eventually cause functioning problems. The sides of the magazine well could not be altered because of the overtravel stops molded into the magazine stampings, but the front and rear could be extended, which Horn did.

The Horn rifle was hammer fired, and used a quite complex fire control mechanism to prevent out of battery firing and bolt bounce. Either of these would be quite dangerous to the rifle, as the bolt was much lighter than would be required for safe firing without the use of the delaying piston.

Horn rifle, bottom view
Horn rifle, bottom view (click to enlarge)
Horn rifle, top view
Horn rifle, top view (click to enlarge)

The Horn bolt was a long affair rather like an automatic pistol slide, with the actual breechface located in the center and a long surface running forward over the chamber. This forward extension added mass to the bolt and also provided the area for the retarding piston to lock into the bolt. It had two wing-like grasping handles at the front to allow easy grasping.

Horn rifle bolt
Horn rifle bolt (click to enlarge)
Horn rifle piston and FCG
A bit of a view of the front part of the FCG…(click to enlarge)

A handful of these rifles were made during the war – the Russians reported capturing 5 at the testing facility at Kummersdorf and another 4 from various units in the field. Horn was one of the engineers they captured, and after the war he continued to develop the concept briefly for the Red Army. Like Barnitzke, Horn reported that when he arrived in Russia, his office from Mauser had been perfectly recreated for him, right down to his coat hanging behind the door. Only the view out the window was different.

Anyway, Russian experimentation was limited to two examples, I believe. Here is one of them, which appears to have been fitted with a pressure measuring device under the chamber. Note the lack of front sight, where the German production guns used StG-style front sights. Also, note the full-hand style of trigger guard, which was copied form the original German production guns. This rifle was designed with the expectation of use on the Russian front, where the ability to use it with gloved hands was an important factor:

Russian trials Horn rifle (right side)
Russian trials Horn rifle – note what appears to be a pressure measuring device under the chamber area (right side – click to enlarge)
Russian trials Horn rifle (left side)
Russian trials Horn rifle (left side – click to enlarge)

In Russian testing after the war, the Horn rifles were found to have a number of deficiencies. For one thing, they were awkward to handle, suffering from being excessively wide and from being poorly balanced, with too much weight too far forward. The charging handles were found to be inconvenient when crawling (they would catch on the ground) and too far forward for easy use when reloading in a prone position. The selector lever was not convenient to use from a firing grip, the buttstock was not attached securely enough, and the magazine release didn’t always work well. Of course, these were rifle still very much in the development phase, and all of these problems could have been addressed.

It seems that Horn had a rather novel and interesting mechanism, and it may well have had real potential had it been developed further. The Russian experiments ended without that development, and I do not know why. Horne did return to the west shortly before his death, but never spoke much about the work he had done in Russia. Interestingly, the only reason he was captured by the Russians was because he had been at the testing center at Kummersdorf when the Russians occupied Berlin – the Mauser facilities and most of their staff ended up in Allied occupation zones.

Three Horn rifles are still in existence, in a museum in Russia. Larry Vickers recently visited and was kind enough to send me these photos of one of the guns (a German example):

I also have some photographs of this rifle being disassembled some time before the advent of digital cameras (they are scanned photographic prints):


    • This looks like a good system for a submachine gun. The bolt would be lighter for a given RoF, so a simple compact and controllable weapon could be produced.

  1. Click here:
    too see disassembled Horn rifle.
    “In Russian testing after the war, the Horn rifles were found to have a number of deficiencies.”
    Yes, poor ergonomics was noted, but on other hand its reliability was incredible high, above linked texts states that 1900 fired without ANY failure caused by mechanism in wide range of conditions: without grease, sand, temperature from -60°C to +50°C.

  2. Fascinating. The Gerät06 seemed much more refined and still cheaper than the Stg44, hence slated for StG 45 status… I wonder to what degree–if at all–Herr Horn may have been influenced by the carbine Williams short-stroke piston on the selbstladekarabiner M1? The carbine taps gas from the barrel quite close to the chamber, which slams a short piston to whack the operating rod assembly/bolt carrier, which moves back while the projectile leaves the barrel, and then cams the rotating bolt out of locking engagement to cycle the weapon. Meanwhile, Horn’s taps gas even closer to the chamber, in fact, from the chamber, to slam a small piston up at an angle to “grab” the slide/bolt extension and hang there until the bullet leaves the barrel and the pressure drops so that blowback/unlocked operation can occur.

    One of Mr. Vickers’ photos shows the Gerät Neumünster or MP.3008 there to the rear of the Horn rifle… Take the Sten Mk.III, and if anything, make it even cheaper ans simpler to produce.

    Thanks all round for the informative brief on this forgotten prototype!

    • Probably not, since the gas bled to piston serves to delay the blowback action in Horn, versus opening the locked action in the M1, very big difference, also I dont think these rifles were available in the Eastern parts of the Reich where Horn was made.

      Ported barrel so close to the chamber also serves in some degree to lower the pressure in the barrel, so it could safely use (by russian account) 0.9kg bolt (compared to vg 1-5 of 1.4 kg)

      One potential flaw of the whole idea and design could be in excess fouling of the piston area, also maybe above than normal erosion…
      Maybe that was the reason of abandoning the Korobov first design.

      Since many russian designers experimented with german captured prototypes, and tried to perfect them (only thing they didn’t have was roller locking), if some russian archives someday open and shed a light on a subject, the gun community would have lot of valuable information that is hidden 60 years without needing to recreate the concepts and results.
      Very little amount of that kind of info flowed out of that country, especially during the Cold War, and west is generally unaware of lot of their technology achievements, sometimes made with fairly crude methods and tools, but with surprisingly effective results.

      • “Maybe that was the reason of abandoning the Korobov first design.”
        So far I know there was not clear technical reason of abandoning this design. Despite it shows good results in test, it was decided to adopt improved AK (AKM).
        In Soviet Union some weapons system were chosen, not because technical advantages, but due to have more support from deciding peoples.
        There is anecdotal story that Degtyaryov convinced Stalin (which favored Degtuarov) that machine gun that prove itself superior in test should enter service, so SG (Goryunov) machine was adopted, as it proved to be better.

      • “One potential flaw of the whole idea and design could be in excess fouling of the piston area, also maybe above than normal erosion…
        Maybe that was the reason of abandoning the Korobov first design.”

        Erosion, yes. Not sure about fouling. The M1 carbine design: “A gas port is drilled at an angle through the gas cylinder and barrel, entering the bore about 4 1/2-in.from the rear face of the barrel. This rearward positioning of the gas cylinder and port makes it possible to take the gas from the bore close to the chamber, before cooling can take place, thus minimizing carbonization.”

        I assure you that Mauser designers would have had access to captured Allied weapons.

        The M1 carbine has a captive piston to operate the operating slide/bolt carrier because it is a gas operated design. The Horn is merely a form of delayed blowback, in which the small captive piston “grabs” to prevent the bolt opening too suddenly. The carbine’s captive piston is returned by the spring-loaded, reciprocating operating slide/bolt carrier while the Horn has a little spring-loaded lever to push against the piston.

        • Maybe the manner it vents, does cause fouling problems, it appears to just blast it out all around the plug around the same gas ring presumably, which given the plug has to fit back into it’s channel again may cause stoppages.

          • “Horn rifle was hammer fired, and used a quite complex fire control mechanism to prevent out of battery firing and bolt bounce. Either of these would be quite dangerous to the rifle, as the bolt was much lighter than would be required for safe firing without the use of the delaying piston.” Maybe a two part assembly would be better i.e. Have a gas plug like of an Sa80 emanating from the the barrel port, with it’s gas piston on top- The Horns plug top being attached to its top, so it vents around the side.

      • ” I dont think these rifles were available in the Eastern parts of the Reich where Horn was made”

        M1 Carbines were common enough that the Germans had an actual nomenclature for them (Selbstladekarabiner 455(a)). Did they issue a whole bunch out? Nope, and probably primarily to units like SD detachments, that were high prominence but low priority for ordnance. But the Germans were certainly well aware of the M1 Carbine and had plenty of examples to play around with no later than 1943. Undoubtedly enough to have examples available to arms designers

  3. Again, top notch material, but as one commenter noted, in original russian article they numbered some good points of the rifle, not just deficiancies.

    However, the (very unconfirmed!) story of “Office replicated in the Russia”, and “Died shortly after return to the Germany and never told anything about time in Russia” is often circulated on the internet these days, with Hugo Schmeisser in lead role, but it seems like it’s become of a generic story, just change the names !

    Its often used by proponents of nullifying the russian effort to the point of “german engineers made everything for them after the war”, which I don’t think is totally false,
    but again all this is speculation and obscure (much like the whole AK story being made/invented by “gifted selftaught tank mechanic”).

    Interesting enough, first (out of few) Korobov 454 design after the war used this very system (speaking of ingenuinity) but I don’t seem to be able to find any pictures of the inside of the rifle, or even closeups, it’s apparent by the elongated barrel trunion area that it is very similar to the Horn/Grossfuss rifle.

    • That link below, mentions the 454 “1947 GA Korobov creates Tula CDB-14 new machine TKB-454-43 (TKB – Tula Design Bureau), the first time equipped with a system of free gas brake light shutter, provides ease of design, cost reduction in the production of and facilitating weapons.” gas brake light shutter is presumably the one with Horn type system.

      Bemusimg Russian transliteration aside “And serves to support the combat larvae during the shot.” Combat larvae…

      • “Combat larvae”
        There is story, I don’t know whatever it is true or not, but is good example of electronic translators “skills”: Americans once developed English-Russian Russian-English translator, to test it they put sentence in EN-RU and its output to RU-EN and compare that with initial input, result was interesting:
        INPUT: The spirit is willing, but the flesh is weak
        OUTPUT: The vodka is good, but the meat is rotten

    • Is there a really good website or book for Korobov’s designs? I’ve become fascinated with rifles that don’t require a gas system and have the operating components centralized in the rear.

      • Lot of ex Ussr info is still in shadows, and waits for the future to be unveiled, but I only hope that it will not be lost or forgotten in the process, since with states that do not have liberal gun laws like Usa, the research and whole gun culture is severely limited and sometimes forcefully hidden from people.

  4. Hm. It occurs to me that by varying the size of the gas port (which governs pressure as per the Venturi principle) and the diameter of the piston (greater cm\2=more total pressure exerted), this system could be tailored to almost any cartridge, up to and including automatic cannon rounds.

    It could not only have made an acceptable assault rifle, it could have been the basis for a simple, easily mass-produced AAA or aircraft cannon. Something that would have come in very handy for Germany about that time.



    • “this system could be tailored to almost any cartridge, up to and including automatic cannon rounds.”
      What about Rate-Of-Fire?

      • Cyclic rate of a full-auto weapon is governed by the following;

        1. Momentum factor of projectile (muzzle velocity x projectile mass);

        2. Bolt mass;

        3. Recoil spring tension;

        4. Locking system (if any).

        Newton’s Third Law of Motion in action. Factor 1 decides how much “reaction” there will be; factors 2-3-4 govern how much resistance to that reaction the system has.

        Generally, straight-blowback or retarded-blowback weapons (like this one) need a heavier bolt to reduce RoF to a reasonable figure, defined as “bolt not moving so fast it either rips head off cartridge case, fails to feed next round, or both”.

        Some weapons get around this by using a “bolt retarder” or “rate reducer” to act as a drag on the bolt either moving backward out of battery or going forward into it. The Skorpion MPs and the Spanish Astra 903 Mauser “Broomhandle” copy had such rate reducers tucked away in their pistol grips.

        To govern the RoF of a heavy auto weapon built on the Horn principle, you would be adjusting the size of the gas port to govern gas pressure exerted on the piston head, the size of the piston head itself, bolt mass, and recoil-spring pressure.

        Note that while the rifle is hammer-fired, there’s no reason an autocannon couldn’t be a fixed firing pin, advanced primer ignition “slamfire” type, as firing from an open bolt wouldn’t be much of a handicap in that application, allowing cooling airflow through breech and barrel between bursts.

        Also note that this helps to reduce RoF still more, as the recoil thrust of the case head has to arrest the forward motion (inertia) of the bolt before it can commence rearward travel.

        In 20mm, I’d figure the RoF at around 550-600 R/M. Keep in mind that for a single-barrel, non-revolver breech cannon, that’s a lot of steel-jacketed HE going downrange every second.

        Enough to put eight or ten rounds in a one-second burst into a Mig-15.

        Or an F-86 Sabre.



    • Calculate the raw materials needed to make aa cannon compared to rifle, plus aa ammo too.

      People are astonished today when they found out that one artillery shell costs like a box full of ak’s…

        • Wars are a bad idea, better spend the money on peasants, mind you peasants need jobs… War production. Which idiot invented the A Bomb.

        • Yeah, but not in the volksturm anything goes phase. They should have thought about rationalizing in ’41, just like Ussr and Gb, in 44-45 it came too late, theyve wasted too much resources on high tech high quality weapons that they start to lose pretty fast after 1943…

  5. It was a novel idea, a product of “last ditch” thinking I think. It probably has potential for future development, it’s interesting that it didn’t require a fluted chamber seemingly as delayed rather than locked system. It’s good this forgotten weapon, has been remembered so to speak.

    • It doesn’t rotate like I thought, the plugs lug thing just rides up and down its angled “rails” because it was never really finished either by the Germans or Soviets it does provide the basis for a “What if” design, if anyone can come up with one. Would this perfected weapon, have become the principle arm of Ze Nazis victorious counter attack using an Zombie army of reconstructed casualties brought about by Mengele.

      • Or the first auto-rifle design that could be built in a post-Smash scenario, because it’s less complex and demands less sophisticated construction materials, techniques, etc., than even an AK-47.