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Explain the different recoil systems, i.e., locked breach, cam, etc.

Discussion in 'Handguns: Autoloaders' started by speedsix, Jan 29, 2009.

  1. speedsix

    speedsix Well-Known Member

    I thought I knew what they were but now I am not clear on the matter. I know blowback, that is easy.

    What is the difference between locked breach, linked barrel and cammed barrel lug? Are there any other common ones? What about that rotating barrel used in the Mauser M2 and Beretta Cougar (I think)?
  2. The Lone Haranguer

    The Lone Haranguer Well-Known Member

    None. A locked breech means the barrel and slide are physically held together for a short distance during recoil until the chamber pressure drops. Links and cams (application and design varies by maker) are what move the barrel into and out of engagement with the slide.
  3. Jim K

    Jim K Well-Known Member

    First, it is "breech" from an old word meaning "rear" (like "breeches" for pants).

    All the terms you mention are used to describe a self-loading (automatic or semi-automatic) gun mechanism. A straight blowback works OK for low power cartridges, but as power increases, the mass that would be required to keep the breech closed until the pressure drops would become too great. If that is not done in some manner, the breech opens too soon and the cartrige bursts, damaging the gun and possibly injuring the shooter.

    So, there have been several ways to keep that breechblock closed, usually by locking it to the barrel for a short period of time. In that way, when the bullet starts to move and recoil begins, the barrel and breechblock (commonly a slide) will recoil together until unlocked by some mechanism in the frame of the pistol.

    One way of locking and unlocking is by lugs on top of the barrel locking into cuts on the inside top of the slide. When the barrel and slide have recoiled together far enough that the bullet has exited the barrel and pressure has dropped, the barrel and slide are unlocked and the slide continues to the rear on its own momentum, extracting the fired case. Then it is forced forward by a spring to chamber another round and re-lock with the barrel.

    If unlocking/relocking is done by a swinging link, it is called a linked barrel mechanism, like the M1911. If the barrel is unlocked by a cam on the barrel contacting a surface on the frame, it is a cam lock action.

    The vast majority of recoil operated pistols today use a cam action, but 1911 type pistols use the original link, designed by John Browning.

    Another way to achieve the same purpose is by locking the barrel to the slide by helical cams, allowing the barrel to rotate during the time needed to keep the breech closed, and the slide to open after the pressure drops, the same as other systems. The rotating barrel system is less common, but has recently been used in the Colt AA2000 (of unhappy memory) and in more successful pistols. Some form of gas operation has also been used, but usually adds enough weight or bulk to the gun that it is not common in pistols.


  4. speedsix

    speedsix Well-Known Member

    So there is locked breech, blowback and gas operated. Most of what I asked about seemed to be some form of locked breech.

    Now that I think of it, I am most familiar with cam locked gun like on my Kahr K-9. I do have a 1911 with the swinging link.

    I also have a Walther P-38. What system is used here? It can't be blowback because it is a 9mm but it has a fixed bbl.
  5. saturno_v

    saturno_v Well-Known Member

    You still can use a blowback system for more powerful rounds.

    For example, the roller blowback system used in the CETME assault rifle (7,62x51 NATO) or the H&K family of assault rifles.

    Two mechanical "rollers" (metallic spheres contained in a enclosure against a sloped plane) delay the blowback effects till the pressure drops and complete the cycle.

    Another solution is to use very heavy mass for the slide (in pistols)

    Typical example are the Hi-Point pistols which can handle 9 mm +P, 40 S7W and 45 +P pressure.

    Their huge and heavy slide is one of the reason they are so ugly, unwieldy and top heavy....but they are cheap and reliable...

    On artillery pieces, where mass and size are not huge problems, the blowback system is used in some applications.
  6. saturno_v

    saturno_v Well-Known Member

    The P-38 is short-stroke locked-breech

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