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Thread: Magazine Burps

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  1. #1
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    Magazine Burps

    Howdy all!

    This question and related malfunction comes up enough to go ahead an use up some bandwidth. Inforthread that might help solve a maddening burp.
    Noyhin' that hasn't been adressed already, but I thought itmight be a good time to post an InfoThread on it.
    ______________________

    Inertia! Just no way to get around Newton's Laws regarding motion.
    Remember the old trick of jerking a tablecloth out from under a table setting? This is the principle at work here.

    We have a round in the chamber and one round in the magazine.

    Bang! The slide starts to move as the pistol torques up and back. The slide holds the last round slightly below the feeding position until it moves far enough to uncover it. Just as the magazine spring is struggling to move the round into position, the round is in a sort of "Limbo" while the pistol continues to move backward in recoil. The round obeys Newton, and stands still while the gun is moving away from it.

    The magazine spring catches up, and gets the round up and into the underside of the feed lips, but because the pistol pulled backward away from it (Even though the pressure from the slide drags the round backward in the magazine)...it settles down forward of the feeding position. At this point, if the magazine spring is strong enough to keep it there, the slide pushes it ahead of the extractor. The pistol either fails to go to battery with the round fully chambered, and the front of the extractor rammed against the back of the rim. Extractor breakage is an eventuality.

    If the spring isn't strong enough, the round is forward of optimum feeding position just as the slide smacks the impact surface in the frame, and triggers a second recoil impulse. The gun makes a short, hard jerk upward and backward...and the round is in limbo once more because the mass of the round has caused the magazine spring to compress slightly. The round...already too far forward in the magazine...jumps the follower, and is free of the magazine. The follower pushes the slidestop up as the slide moves forward, and the slide locks. If the magazine spring is weak enough, the next to last round will be ejected from the magazine, and the last round feeds. Ever found live ammo among your brass? Heeere's yer sign!

    The problem is two-fold. One is the spring that has fewer coils to make room for the extra round. There is ample tension to feed until it gets to the last round...and tension is at a mimimum...but sometimes it can happen before the last round. Upping the spring rate helps, but doesn't address the other issue.

    The other part of the problem is the smooth follower. Browning knew how
    inertia would affect things, and he put a small dimple on the top of the magazine follower. The dimple's function is two-fold. It adds a small amount of height to the follower in order to give it a "Leg Up"...and it stops the forward movement of the round. More accurately, it keeps the pistol from moving out from under the round in recoil. In this function, it's basically a back-up for the spring as it fatigues, and provides a better opportunity for the round to stay in position to be stripped from the magazine by the slide instead of being pushed ahead of it...or... in the extreme cases, escaping from the magazine completely.

    John Moses designed a 7-round magazine and he put a dimple on the follower for very good reasons. Whenever we try to change things in order to "improve" the gun...we very often cause problems. There just ain't no such thing as a free lunch, I'm 'fraid.

  2. #2
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    Thumbs up

    Commandante:

    Tuner's too shy to ask, but I'm not - please make this one sticky....

    (And delete this after he's seen it.)

    Tuner: Ever drop a message on somebody and get back: "I've printed out your message to study later when I have time."?

    That usually translates to "D'oh?", of course, but in this case, it's "Good Job!"

    Thanks!
    Stu.
    (Why write a quick note when you can write a novel?)
    ΜΟΛΩΝ ΛΑΒE
    יזכר לא עד פעם

  3. #3
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    OK, here we go.

    'Tuner, I've been thinking about what you say ever since the first time I read it, and I have a problem with one small part of it, and I have a question about another part of it.

    Your theory is based on the premise that the round stands still, according to Newton.

    Now, that would be true, but Newton specifically says "in the absence of outside forces...".

    In this scenario, the round is, in fact, always under the influence of a significant outside force- the round is always in contact with the follower, the mag lips or the breech face- I don't see where it's suspended in space, free of external pressures. Therefore, it obeys Newton by going with the external forces, not by standing still.

    The part I have a question about is you seem to say that when the mag is in the weapon, and the slide is closed, that the slide actually pushes down on the top round, depresses the mag spring, and pushes the top of the top round below and out of contact with the mag lips.

    Is this so?

  4. #4
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    Absence of outside Force

    Hey Jammer!

    Outside force is always acting on any object that has mass and weight and that force is gravity...but even in the absence of gravity, the object still has mass...and thus resistance to acceleration. Go back to the tablecloth trick. You've seen the magician jerk the cloth out without disturbing the glasses, even though the glasses were in contact with the tabletop and the cloth. Push down on the glasses to increase the downward force, and the trick won't work because the cloth will drag the glasses along with it.

    The round tends to stand still due to its resistance to acceleration...An object at rest tends to remain at rest. If the mag spring tension is great enough to overcome the inertial resistance that the round offers to acceleration, the round will move backward with the gun. if not...It tries to stay where it is prior to recoil. Up the spring tension and the follower offers more friction, and takes the round with it. The dimple's job is to insure that the round doesn't jump the follower by providing a solid resistance that doesn't rely on friction alone.

    Think of how small the area of contact is between the side of the case and the top of the follower. Not much to offer there, even if the spring doesn't wimp out and let the round float.

    Yes..When the loaded magazine is locked in place, the spring is compressed a little by the slide. That's why a magazine locks in easier when the slide is locked back than when it's in battery. Try it!

  5. #5
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    Isn't the surface of the dimple smaller than what the surface of the follower would be against the side of the last round?

  6. #6
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    Smaller?

    Quote Originally Posted by Jammer Six
    Isn't the surface of the dimple smaller than what the surface of the follower would be against the side of the last round?
    It matters not, young grasshopper, for the dimple catches the rim as the round tries to slip past on its way to freedom, and thus imposes a physical barrier to escape. In this manner, the cartridge achieves true understanding of the reasoning of Saint John Moses....

  7. #7
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    Talking

    Tuner:

    I did the "grasshopper" bit in a reply to a friend's message on a CompuServe forum a few years ago.

    I didn't realize what I'd done until I got his reply a day or two later.

    His name was Jack Hopper....

    (Where can I get a good ear pointer? Mine getting sloppy are.... )
    Stu.
    (Why write a quick note when you can write a novel?)
    ΜΟΛΩΝ ΛΑΒE
    יזכר לא עד פעם

  8. #8
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    tuner's five minutes of fame

    After a few fixes via personal message and tongue lashing by reply, I have learned that Tuner is the real deal. His reasoning about the dimple and adequate spring tension are on the money. I lean more toward spring tension than anything else,but I as well as you am "grasshopper".

  9. #9
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    Smile Amen!

    Quote Originally Posted by lil toad
    After a few fixes via personal message and tongue lashing by reply, I have learned that Tuner is the real deal. His reasoning about the dimple and adequate spring tension are on the money. I lean more toward spring tension than anything else,but I as well as you am "grasshopper".
    Tuner may not always be right, but his track record is a lot better than mine .

    He definitely knows what's going on inside a 1911.

    WAY more than I do, being a perfect example of "too much knowledge being a dangerous thing, and not enough knowlege is even more dangerous."

    I'm not sure if I'll ever forgive him for not coming outside to see me when the new wife and I were driving by in 1975, but that's another story .

    IAC, I'm here to learn, and to share. Sometimes asking the right question will lead to an answer nobody suspected. Or a good laugh....
    Stu.
    (Why write a quick note when you can write a novel?)
    ΜΟΛΩΝ ΛΑΒE
    יזכר לא עד פעם

  10. #10
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    Stu, back in 1975, Tuner might have been busy with a ... new wife too! LoL
    John Caradimas SV1CEC
    The M1911 Pistols Organization
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