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Thread: Premature Slide lock

  1. #11
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    Quote Originally Posted by Steve in Allentown View Post
    It's purpose isn't so much to add upward pressure against the cartridge. Rather, it's purpose is to prevent the forward movement of the cartridge by catching the rim. It's sort of like a speed bump.
    That is more my understanding. But that only applies to the last round, correct?

    The last round isn't going anywhere, until it is actually the last round.

    For the other rounds, the rim of the top round should catch slightly on the extractor groove of the round below. That's assuming that the case sides lie tight against each other.

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  2. #12
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    Quote Originally Posted by megafiddle View Post
    That is more my understanding. But that only applies to the last round, correct?
    Yup. We know that the potential for an inertia feed is greatest with the last round which is why the follower bump is of a specified dimension and at a specified point on the follower.

    For the other rounds, the rim of the top round should catch slightly on the extractor groove of the round below. That's assuming that the case sides lie tight against each other.
    My gut tells me that it doesn't but I honestly don't know if that happens. I'll bet someone else here does know.

  3. #13
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    The early cartridge cases had a cannelure in the brass to eliminate bullet set back. The dimple lines up with the cannelure.

  4. #14
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    Quote Originally Posted by Steve in Allentown View Post
    ...
    My gut tells me that it doesn't but I honestly don't know if that happens. I'll bet someone else here does know.
    It is slight, and possibly insignificant, but it can be felt when pushing rounds out of the magazine by hand.

    I should have said that I didn't believe it was by design.

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  5. #15
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    Quote Originally Posted by megafiddle View Post
    It is slight, and possibly insignificant, but it can be felt when pushing rounds out of the magazine by hand.

    I should have said that I didn't believe it was by design.
    I have to disagree.

    John Moses Browning was a firearms design genius. Nothing he did was an accident. That dimple (or pimple, or whatever you choose to call it) is an extra step in the manufacturing process. It cost Colt (his client) a couple of cents to put that dimple in each magazine they made. There was a reason for it. Therefore, it was "by design."
    Hawkmoon
    On a good day, can hit the broad side of a barn ... from the inside
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    Rick McC. (17th October 2020)


  6. #16
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    When the dimple falls into the cannelure of the last cartridge it retards inertia induced forward motion preventing double feed of the last round when spring compression is the lowest.

    Magazine followers of the earlier pistols, 1908 and previous, didn't have a dimple. As I recall the earliest developmental .45 model magazines, 1910 and previous, didn't have a dimple. It was evidently enough of a problem to change the design of the follower.

  7. #17
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    Quote Originally Posted by Doran View Post
    When the dimple falls into the cannelure . . .
    So, the pimple/dimple/divot/bump isn't meant to engage the case rim. Does this mean that pimple/dimple/divot/bump is useless unless the case has a cannelure formed into it?

  8. #18
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    Quote Originally Posted by Steve in Allentown View Post
    So, the pimple/dimple/divot/bump isn't meant to engage the case rim. Does this mean that pimple/dimple/divot/bump is useless unless the case has a cannelure formed into it?
    Not at all. The bump creates a small area with considerably higher unit force/pressure than would be the case if the follower were flat and the entire length of the case was in linear contact along a narrow like.
    Hawkmoon
    On a good day, can hit the broad side of a barn ... from the inside
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    Doran (17th October 2020)


  9. #19
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    Quote Originally Posted by Hawkmoon View Post
    I have to disagree.

    John Moses Browning was a firearms design genius. Nothing he did was an accident. That dimple (or pimple, or whatever you choose to call it) is an extra step in the manufacturing process. It cost Colt (his client) a couple of cents to put that dimple in each magazine they made. There was a reason for it. Therefore, it was "by design."
    I was referring to the case rims catching on the extractor groove of the round below.

    Nominal spec allows the case rim to protrude very slightly above the case wall proper. Tolerances allow the rim to sit below the wall, and in that case they would not catch.

    I cannot find any reference to the magazine follower dimple in the Browning patents.

    Did Colt later incorporate the dimple?

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