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general semi-auto question

Discussion in 'General Discussion' started by gipper, Mar 30, 2004.

  1. gipper

    gipper New Member

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    I've noticed some guns, (wish i could spout off the brands) but, when the slide is back the barrel looks tipped up, wondering why this is on some guns but not others
  2. Remington597

    Remington597 Former Guest

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    Centerfire vs. rimfire. The age old debate. :D
  3. JohnK3

    JohnK3 New Member

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    *BZZZTTTTT*

    Wrong! Thank you for playing!

    Some semi-autos use what's known as a "short-recoil" locking mechanism to keep the bolt locked to the barrel until the gas pressures drop to a safe level. In these systems, the barrel actually travels with the bolt for some distance until the pressure drops enough for the action to unlock. The 1911 uses a short-recoil action, as does the FN Browning HP-35, the CZ75, the Glock and most other 9mmX19mm and larger semi-auto pistols. In these pistols, the barrel must tilt in order to "unlock" from the bolt. In most cases, the bolt is an integral part of the slide.

    Some (but not all) smaller pistols, such as the Beretta Tomcat in .380 and .32 caliber, the Walther PPK/PPKS and other small pocket pistols, use a "blowback" action, where the slide has enough mass and the spring enough resistance to provide the locking mechanism through sheer inertia. In these, the barrel is fixed in place and doesn't move, just the slide/bolt moves. Some of these, however, tilt the barrel during disassembly, but not during normal operation.

    .22LR/Rimfire pistols often use a blowback mechanism, which leads to the "rimfire vs. centerfire" idea. It is incorrect, however, to assume that only rimfire pistols have "fixed barrels" that don't tilt.

    Then, there's the Luger. It has a toggle-action, rather than a blowback or short-recoil action. Fixed barrel, but complex locking mechanism.
  4. gipper

    gipper New Member

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    Very interesting stuff, thanks john
  5. Remington597

    Remington597 Former Guest

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    John:
    Thanks for that great and indepth clarification.
  6. JohnK3

    JohnK3 New Member

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    No prob.

    Was just raggin' you a bit with the "BZZZT" bit. [grin]

    I've been interested in how guns work for a long time. Explains why I joined ROTC: in order to take the "Weapons Theory" class in college!

    Interesting note: The Thompson M1A1 uses a blowback mechanism fired from an open bolt. Blowback's too big for a handgun in that caliber, but works like a charm for a carbine!
  7. Xracer

    Xracer *TFF Admin Staff Mediator*

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    Minn-eeee-sota, ya, sure, you bet!
    Nice explanation John.

    And now for a bit of trivia:

    The original Thompson design (up to the M1928) used a locked breech system of wedges known as the "Blish System", based on the friction between dissimilar metals.

    When they ramped up production for WWII, they simplified the design by simply eliminating the locking device.....and, of course, the M1 Thompson worked just as well without it.

    Also, there was one high power pistol that used a straight blowback system.....the Astra 400 in 9mm Largo. However, the recoil spring was so strong that, if you weren't very careful, disassembling that sucker could be damn near lethal! :D
  8. JohnnyRobotic

    JohnnyRobotic New Member

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    yah my fathers glock does that, the 17 but it doesn't do that on my sw1911, thanks for the explanation i was wondering why it did that
    Last edited: Mar 31, 2004
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