Operating Systems 201: Tilting Bolt Locking

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Locking systems we have previously covered include tilting barrel locking, the most common pistol locking mechanism, and rotary bolt locking, the most common rifle locking mechanism. However, at one time another locking mechanism was widely believed to be optimum for military rifles, due to its simplicity of manufacture and compact design. This was the tilting bolt locking mechanism, and it was incorporated into many famous and successful designs, including the SVT-40, SKS, StG-44, and FN FAL.

Tilting bolt locking is similar to tilting barrel locking, but it is essentially reversed. Instead of the barrel tilting into alignment with locking surfaces in the moving parts group, the breechblock is the tilting element, and it is cammed into its locking position by another element, such as an operating rod or bolt carrier.

  • Operating rod: A long rod-like element of the moving parts group that interacts with another element, often the breechblock,¬†and transfers momentum to it which is used to operate the action.
  • Bolt carrier: An element which cradles and supports the bolt, protecting it from the elements, and which also often actuates the locking mechanism.

We will discuss bolt carriers and operating rods in more detail later. Now, we can see how the tilting bolt system works in the photos shown below of a MAS-49. In these photos, the bolt carrier has been removed to show the action of the bolt:PHOTO_20160613_235016fixed2 PHOTO_20160613_234942use2

Notice how the rear of the bolt moves down to prop the breechblock against the back of the chamber. The locking surfaces of the MAS-49 are shown highlighted in red in the photo below:

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Note that in some designs, the bolt does not tilt down to lock; in the Polish wz. 38M, for example, the bolt tilts up to lock, while in the Czech ZH-29, it tilts to the side. The tilting bolt system of locking was valued for its strength, capable of handling high pressure rifle rounds, its compactness, and its simplicity of manufacture. However, it eventually fell out of favor, being supplanted by the rotary bolt in most modern applications, partly due to the tilt locking system wearing more quickly, and partly due to less potential for accuracy. Still, despite being hardly used at all today, the tilting bolt locking system still has a lot of promise.



Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • CoyoteVigilant

    Can’t forget the Swedish AG42B. The tilting bolt is very similar to the SVT40.

    I found my AG to be very accurate to 100m. Compared to my SVT40.

    • The_Champ

      Indeed, as pointed out by Nathaniel, there is quite an illustrious list of tilting bolt firearms. The SVT-40, SKS, StG-44, MAS49 and FN FAL as he mentioned. The AG42 and its Egyptian derivatives as you pointed out.
      Add the FN SAFN and zB vz 26 and its famous derivative the Bren Gun. And speaking of Czech guns add the VZ52 and VZ58.

      I’m sure I missed a few but those alone amount to an impressive list of well regarded firearms.

      • CoyoteVigilant

        I would love a MAS49. But they seem very hard to get and somewhat expensive here in Canada.

        As for the VZ58 that is a falling block not a tilting block.

        • The vz. 58 uses a tilting locking block system, something it shares with the Walther P38 and Beretta 92, and which I’ll discuss later. The vz. 52 rifle uses a unique front-tilting bolt arrangement.

          • The_Champ

            I’ve haven’t really got to play with the innards of the 52 and 58. Would you classify them as something completely different than tilting bolt, or more of a subset of the general idea?

          • I would classify the 52 as a forward tilting bolt, and thus essentially within the purview of this article.

            The 58 accomplishes essentially the same thing, but with a locking block instead of tilting the bolt to lock.

          • CoyoteVigilant

            Strange, I don’t have a 92 or P38 to compare, I always thought the 58 was a falling block as it drops down and it’s a 2 piece affair. Maybe I need to look at my 58 a bit better….

          • Nope, it tilts, although if you have the bolt group together it does look like it falls.

        • plingr2

          Yeah, VZ 58 is quite similar to p38 or Beretta 92.

      • Red79cj5

        My favorite little fun gun the SKS

  • HKmaster

    What’s the name of the gun on the thumbnail? Looks like a 9mm StG 44 :0

    • pbla4024

      Franchi LF58 in 30 carbine

  • bull

    i think weight was also a big factor that tilting bolt lock disappeared. since the receiver has to take the force it has to be beefier -> heavier.

  • Wolfgar

    Tilting bolts tend to vertical string on a target when the magazine pressure on the bolt changes as the magazine empties. FN FAL’s are notorious for doing this.

  • Fox Hunter

    Dont forget the VZ58

  • IndyToddrick

    Those pictures aren’t “doing it” for me. I understand it is opposite of tilting barrel, but I guess I’ll go Google it to learn more :-).

    • DisqusBlows

      Not having a photo showing more of the rifle makes it extremely hard to put in context for the target audience (namely those of us that have not seen that action before).