Operating Systems 101: Short-Recoil

    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. He can be reached via email at [email protected]


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