How Does It Work: Roller Locking

Roller locking is a system that is not used in many guns and often confused with roller-delayed blowback – which is understandable, given the similarities between the systems. Roller locking is really a sub-type of flapper locking mechanism. It was most significantly used in the MG42, and also in the Czech vz.52 pistol. In essence, it uses rollers in place of flaps to lock the bolt and barrel securely together during firing, and depends on an external system (short recoil, in the case of the MG42 and vz.52) to unlock before it can cycle.

46 Comments

  1. It may have been rarely used by most manufacturers, but Heckler and Koch used nothing else but roller locking for a very long time, and built a truly stupendous number of weapons using it, in calibers ranging from 9 x 19mm on up to 12.7 x 99mm. The latter being the HK25 machine gun, of which maybe one at most was ever made.

    Also, beginning with the MG42, there have been a huge number of GPMGs in German wartime and then NATO service under such designations as MG1/2/3 (Germany), MG42/59 (Italy), and etc. that used the “Stecke” lock. In fact, that was an MG42-type bolt Ian was using to demonstrate the action with next to the Vz52 pistol.

    Probably the smallest roller-locked MG was the CETME Ameli in 5.56 x 45mm, which is also probably the most lightweight and compact 5.56mm SAW ever made anywhere. I don’t believe that even the Ultimax 100 can be broken down and carried in a briefcase like an MP5K or Sten MK II. The Ameli can be.

    And of course the Swiss Stg57 family of rifles and the follow-on SiG 530-550 series all use the roller lock. As Ian has commented, in the StG57, the roller lock is grossly overengineered compared to that in the HK91/G3 series, because while the HK was originally designed by CETME in Spain for the 7.9 x 33mm Kurz round and then “up-calibered” to 7.62 x 51mm NATO, the Swiss version was designed from the start for the 7.5 x 55mm Swiss cartridge, with velocities and pressures in the range of the German 7.9 x 57mm or the U.S. .30-06.

    Please note that the United States Navy Bureau of Ordnance once made up a Savage Model 99 lever-action breech assembly in .50 BMG, just as an experiment. It worked perfectly well. There are a surprising number of breech actions from the 19th Century based on principles that could resurface in automatic actions, even today.

    A .50 BMG heavy machine gun based on either the HK roller-locked action or the Savage 99 breech would be interesting, to say the least.

    cheers

    eon

    • Do you think a gas “delayed” roller lark (as opposed locked; differentiating between the 9×19 and 7.92x57mm job) .50bmg would work; Instead of a “mass” that engages the rollers from the rear, how about gas from the front or even a combo of both. Essentially you just put the angled surfaces on a gas plug with a port in the barrel “front of the cases neck” gas hits the plug, angled surfaces can’t move for a period via pressure. That hk25 is a bit of a unicorn I can’t find one.

      • My Premise is that the Horn rifle didn’t appear to have a fluted chamber, suggesting gas gives more of a delay than a mass.

        • How about this two angled surfaces; one gas as above one mass as per the delayed lark “rollers inbetween” Very simple abd lightweight, who’s got a hacksaw & a hammer and a spare M2? Course it will work, hit it with the hammer; fixed.

          • Inertia, use a strong spring. Its not inertia anyway its pressure on the bolt translating to the rollers, which push back the mass.

          • Or the mass can’t contain the pressure, so the rollers pinch via moving the mass; he may well have noticed bolt bounce but regardless; hammer down on the “bolt” in Hk’s, no bounce.

          • “(…)Very(…)lightweight, who’s got a hacksaw & a hammer and a spare M2?(…)”
            How lightweight are you calculating it to be? I would not be surprised if you claim machine gun firing 12,7×99 NATO cartridge which is lighter than M2 Browning, however it is rather due to latter being relatively heavy.

    • Eon,
      As Ian noted above, “Roller locking is a system that is not used in many guns and often confused with roller-delayed blowback”. He is absolutely right. All those HKs, the Ameli, and those Swiss rifles are roller-delayed blowback.

    • Eon, this is the first time in your many excellent contributions that I have to disagree with one point.
      As far as I know, it was George Chinn who brought up the opinion that the mechanism patented by Edward Stecke on Poland was the basis of the MG 42. If you look at the patent (and the excellent drawing in Chinn’s book) it is obvious that Stecke has invented a delayed blowback mechanism, using kidney shaped levers. The MG 42 being a locked breech, I do not quite understand how Chinn came to his opinion. Please have a good look at the Stecke design yourself and the decide if you agree with Chinn.

    • “(…)Probably the smallest roller-locked MG was the CETME Ameli in 5.56 x 45mm, which is also probably the most lightweight and compact 5.56mm SAW ever made anywhere. I don’t believe that even the Ultimax 100 can be broken down and carried in a briefcase like an MP5K or Sten MK II. The Ameli can be.(…)”
      Does STONER 63 count as MG? If yes it is marginally heaver when empty:
      Ameli – 5,3 kg according to https://modernfirearms.net/en/machineguns/spain-machineguns/cetme-ameli-eng/
      Stoner 63 – 5,31 kg according to https://modernfirearms.net/en/assault-rifles/u-s-a-assault-rifles/stoner-63-eng/
      and taking in account its modular nature should be relatively easy to break into few parts, though I do not if it would be possible to pack all into briefcase.

    • “, but Heckler and Koch used nothing else but roller locking ”

      Sorry, but you are wrong. H&K used roler delayed mechanisms for a long time. Not mechanically rigid locked actions(*). They even investigated a 12,7*99 mm chambered machien gun based on this principle. For obvious reasons they gave up on it. Oh and the spanish AMELI machine gun is also roller-delayed.

      The bolts Ian uses to demonstrate look like to be from an Austrian MG74 hence one of them being much bigger to reduce cyclic rate as is normally issued with every MG74 and a normal MG42-ish bolt. The bolt of an MG3 is machined with straight lines all over and no rough casting surface.

      (*)Although H&K has manufactured parts for the MG3 at times like barrels and replacement bolts & carriers.

      Really, you have been reading, watching and posting here on Forgottenweapons.com for so long, you should have picked up on the differences by now.

  2. Roller locking gets built in unlocking guide cams and after short recoil of barrel and slide, unlocking occurs through an ascending speed and force against to locking recesses… Needs powerfull slide material and hardness. lMHO.

  3. Ian pointed out roller lock operation with recoiling barrel as opposed to roller DELAYED operation with non-moving barrel. Many people are mixing it up as a pattern of mental inertia.

    There is still one possibility which is combination of roller lock activated by gas piston. I believe there was one such case in development by Mauser, but was not fielded. This may be something to consider since rollers do not wear with time and their actuation does not require helical cam. Disadvantage perhaps may be greater receiver bulk in area of lockup.

    • “Do not wear with time”

      But do wear with use… 😉

      I see where you are going with that, the roller (if it is a proper roller rather than the Swiss flap) can roll so that it distributes wear around its surface

      And it also distributes wear more evenly on the locking seats of the bolt and the receiver, compared to a rotating bolt or a locking block.

      Cylindrical rollers and cylindrical seats are also fairly easy to generate smoothly and accurately, and do not cause as severe stress concentrations as (for example) the relatively square and sharp roots of locking lugs and the inside of receiver rings.

      That said
      A roller introduces a third set of tolerances, and it is slightly more difficult to gauge the position of a cylindrical recess than it is to gauge a flat planar locking surface.

      A roller doesn’t sweep dirt out of the way either.

      • “Cylindrical rollers and cylindrical seats are also fairly easy to generate smoothly and accurately, and do not cause as severe stress concentrations…” – correct!

        Also, machining motion derives from rotation and most common tools are cylindrical (reamers, end-mills). Roller is easy to make out of say O-1 drill rod or A2 – cute and face; stock is centerless ground – very accurate.

    • “(…)Mauser(…)rollers do not wear with time and their actuation does not require helical cam(…)”
      Looking at aerial machine guns and auto-cannons made by Mauser AG during WWII suggest that they considered locking by rotation more suitable for that application, namely it was used inside:
      MG 151 machine gun
      MG 151/20 auto-cannon
      second was in usage for long time after 1945, hinting that it did not wear too quickly

    • Mauser Gerat 02 – roller-locked G43. Gerat 06 – early experimental roller-locked gas piston version of the “STG45”. MG215 prototype aeroplane machine-gun. I think.

    • The most interesting example of a gas operated roller locking firearm I can think of, is the TRW ‘Low Maintenance Rifle’ of the early 1970s. A fascinating full auto only open bolt design, that was intended to be cheap to make and simple to operate.

  4. Just for the sake of playing devil’s advocate (or troll) with the frequent confusion between roller locking and roller delay

    How about a truly roller locked breech, that is unlocked by an inertia block that stays almost stationary while the rest of the gun recoils?

    Throw in a fluted chamber (whether it needs one or not)

    It’s almost worth building such a gun and feeding marketing press releases to the hapless gunzines and their (either hard of thinking, or else ‘Tegriddy-free whore) writers.

    How much confusion could that cause?

    • Keith in England “I am in England also, clearly” are doubtless an excellent engineer; but as for you and inventing… You’d be questioning the button in caveman times.

      Amyway, inertia is it Hk roller delay.

  5. Its not inertia is it, because of the hammer falling in HK models unlike in say the Gerat 06h. With no hammer.

    • “The bolt doesn’t bounce” prove it does and I will not be the black knight limbless refusing to accept defeat.

  6. Ian – “Roller locking is a system that is not used in many guns and often confused with roller-delayed blowback – which is understandable, given the similarities between the systems.”

    First Post – “Let me demonstrate your point with my utter conflation of the two systems.”

  7. With 47 years of playing with roller locking I think that gas operated locked using a gas system similar to the AR18 is best.Henk Visser always said the G3 etc should have been roller locked and that delayed blowback stopped the guns being what they could have been. Henk was a director of HuK and also owned the roller locking patent. He had built a 7.62 x 39mm G3 that worked well. The advantiges of using a gas system are no fluting, slower bolt speed and ejection and easier to breech up using different size rollers that can also be used to correct wear Also the barrel extensions can be made of cheaper steel. For further reading the Forgotten Weapons blog on theGerat 06 and 06(H) is very instructive

  8. This is confusing …
    Why explain the difference between positive roller locking and roller delay, using two systems with the same positive locking and short recoil as an example? …

    Am I losing my mind, or was I missing something? ..
    Or just Ian didn’t have a bolt from G3 or MP5 in his hand?
    Or does Yen not understand the difference in work between G3 and MG3? ..
    Or…

    • What happened to the HK 25 50 cal machine gun? Is it even possible to create such a thing with a roller-delayed blowback mechanism?
      IMHO yes. What do you think?

  9. What happened to the HK 25 (50 cal machine gun)? Is it even possible to create such a thing with a roller-delayed blowback mechanism?
    IMHO yes. What do you think?

  10. This is an interesting question.
    Theoretically, nothing gets in the way. You “just” need to take the MG21 and proportionally increase it for a larger cartridge.
    It seems that such a machine gun “in the metal” never existed.
    Perhaps there was something like a preliminary draft on paper. With calculations and estimates, without which the Germans cannot live.
    Perhaps a technical test bench was built.
    In any case, I think that the project was declared dead as soon as these “clever people” realized that for the .50 machine gun there was an extensive gamut of ammunition very significantly different in recoil momentum. And systems with a roller delay are extremely sensitive to this and normally work only on “their” cartridges.

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