Operating Systems 101: Short-Recoil

Image courtesy of C&Rsenal

Image courtesy of C&Rsenal

Two basic mechanisms dominate the field of handguns today: The aforementioned straight blowback system, and short-recoil operation. The latter of two is a mechanism as clever as it is old; the first short-recoil weapons date back to the latter half of the 19th Century!

Short-recoil harnesses the same principle of inertia as does straight blowback, but it does so differently. Instead of the round’s thrust simply forcing the breechblock apart from the barrel, short-recoil weapons include a locking mechanism coupled with a barrel which can move independently of the frame, to force the cartridge to act against the combined inertia of both the barrel and breechblock together, for a short time.

  • Locking mechanism: A mechanism that causes physical interference between the breechblock and the barrel, which solidly prevents them from separating until the lock is de-activated during the course of operation.

The way it works is this: The cartridge is ignited, which produces thrust against the breech face, forcing it to the rear. The breechblock is locked against the barrel, so the barrel and breechblock move to the rear as a unit for a short time. This rearward movement then causes the locked barrel and breechblock to interact with a mechanism that unlocks them, stopping the barrel’s rearward movement before it overrides the feed device, and allowing the breechblock to travel all the way to the rear by its own momentum combined with the force of residual gas pressure.

  • Breech face: The surface of the breech against which the rear of the cartridge bears.
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This animation of a Swedish Lahti m/40 illustrates short-recoil operation. Note that the breechblock is fixed to the barrel by a locking piece, which disengages during the rearward travel of the breechblock and barrel. An accelerator lever gives an additional kick to the breechblock in the Lahti; this is not a universal feature for short-recoil firearms. Image courtesy C&Rsenal.

 

Short-recoil is a capable operating mechanism well-suited to almost all ammunition types, that can also be made to be inexpensive and very durable and reliable. It is a popular mechanism for handguns and machine guns due to its simplicity and reliability, although because of their moving barrel it is a challenge to produce a short-recoil firearm capable of great precision, so it is rarely used for target and sniper weapons.



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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  • Pete M. – TFB Writer

    Why don’t we see more modern short-recoil guns?

    It also looks like short-recoil would be a good suppressor host? With the cycle starting but delaying ejection a few extra milliseconds?

    • If you mean like the Lahti? Cost and size. You ever handle a Lahti m/40? It is one gun that makes a Beretta 92 seem reasonably sized. Lots of parts = lots of money too.

      • Alexandru Ianu

        Size isn’t exactly an issue for military handguns – they’re not made for concealment, and the Lahti is certainly less complicated than the Luger.

        Short recoil can also make for a very light and handy long gun (check Forgotten Weapons for the Mannlicher 1901/1904 carbine), and it can also be made very inexpensive as you can get away with less milling operations than something that is a rotating bolt gas operated system.

    • ostiariusalpha

      All the modern tilting barrel designs are short recoil, which is not ideal for a suppressor host, but obviously still happens (like on an HK Mk. 23). They do have modern pistol designs with in-line recoiling barrels, such as the Arsenal Firearms Strike One/Стриж.

      • Pete M. – TFB Writer

        Good info thanks. So tilting barrel designs are short recoil? I thought short recoil was analogous to in-line.

        • DaveP.

          It doesn’t have to be. All you need is for the barrel to travel locked with the breech face for a short distance before separating for the ejection/reloading cycle. 1911’s are short recoil, as an example.

        • ostiariusalpha

          Nyarp. Short recoil has several subdivisions of mechanism: Toggle Lock, Locking Block, Rotating Barrel, and Tilting Barrel.

          • Pete M. – TFB Writer

            Thanks to you both for the explanation.

        • You work here?

  • Jack Morris

    Nathaniel, I am loving this series! Very informative and thoughtfully written. Looking forward to the rest. Keep up the great work!

  • Allan

    I would like to see more articles like this especially one on long recoil operating systems and blow forward systems .

  • Aaron E

    Great work Nathaniel!