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Thread: What causes magazine spring fatigue?

  1. #1
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    What causes magazine spring fatigue?

    In summary:

    Constant compression from being fully-loaded does not cause spring fatigue.

    Repeated compression/decompression cycling causes spring fatigue by causing and propagating micro cracks in the bends of the wire.

    Stretching springs is not only ineffective at "rejuvenating" springs but it causes / accelerates the same micro cracks that cause spring fatigue.

    If anyone has access to and can link a copy of Technical Report ARWSE-TR-16035 please do so.

    I've gotten this from multiple sources over the years but the latest mention, prompting this post, was this from the CA National Guard Shooting Team FB page:

    https://www.facebook.com/CombatShootingTeamCMD

    What causes magazine spring fatigue? Constant compression from being fully-loaded, or repeated compression/decompression cycling?

    Can you pre-load magazines and keep them in extended storage without concern about spring fatigue?

    Should you have multiple sets of magazines to cycle ammunition into and out of?

    We have the answer, and it might surprise you.

    The US Army Armament Research, Development and Engineering Center at Picatinny Arsenal set about finding the answer, and published their findings in Technical Report ARWSE-TR-16035, “Performance of 5.56mm 30 Round Magazines After Extended Loaded Storage,” August 2017.
    300 magazines were fully loaded, and for the next 5 years 30 magazines were fired for performance data collection every 6 months.
    Spring pressure was measured when the test began, and again at the time the magazines were pulled from storage. Stoppages were counted during the live fire testing.

    The data analyzed and published:

    NOT A SINGLE MAGAZINE-RELATED STOPPAGE.

    The next time you deploy, you can be confident that the pre-loaded magazines sitting in your vehicle bailout bag, or in ammo cans secured in your vehicle are reliable.

    And, you certainly won’t have to buy multiple sets of magazines to swap your ammo in and out of, over the course of your deployment, like I used to do.
    Just load your magazines, and keep them clean and protected. They’ll be fine.

  2. #2
    Site Supporter farscott's Avatar
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    Constant compression from being fully-loaded does not cause spring fatigue IF the spring's full compression in that application is within the specification for that material. Many springs are compressed too much and can be damaged by full compression in the application. This is a common issue when companies try to squeeze another round into a magazine without adding length.

  3. #3
    Old man yelling at cloud OlongJohnson's Avatar
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    How is it that engine valve springs can go 300,000 plus miles without the first problem, but gun springs are typically toast at several orders of magnitude fewer cycles?
    .
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  4. #4
    Quote Originally Posted by farscott View Post
    Constant compression from being fully-loaded does not cause spring fatigue IF the spring's full compression in that application is within the specification for that material. Many springs are compressed too much and can be damaged by full compression in the application. This is a common issue when companies try to squeeze another round into a magazine without adding length.
    This seems to be constantly overlooked by the "only cycles of compression/decompression wear out springs" camp. Creep is totally a valid concern if the spring was not properly specced for its use, which I could see being an issue with guns, particularly when you get into things like modified followers or extended magazines created by welding multiple mags together. Even with OEM mags, I could see it being an issue due to lazy engineering and/or lack of real analysis.

  5. #5
    Site Supporter snow white's Avatar
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    I see feed lip separation being possibly a more realistic outcome than spring fatigue, regarding keeping mags loaded for long periods of time. Metal mags of course.
    Come, mother, come! For terror is thy name, death is in thy breath, and every shaking step destroys a world for e'er. Thou 'time', the all-destroyer! Come, O mother, come!

  6. #6
    Quote Originally Posted by farscott View Post
    Constant compression from being fully-loaded does not cause spring fatigue IF the spring's full compression in that application is within the specification for that material. Many springs are compressed too much and can be damaged by full compression in the application. This is a common issue when companies try to squeeze another round into a magazine without adding length.
    Which describes what is going on when a vendor says to leave his stiffly sprung extra capacity magazine loaded for a week to squash the spring into a functional state.
    Code Name: JET STREAM

  7. #7
    Quote Originally Posted by OlongJohnson View Post
    How is it that engine valve springs can go 300,000 plus miles without the first problem, but gun springs are typically toast at several orders of magnitude fewer cycles?
    I suppose, gun springs get more compressed than valve springs. For example see this valve spring in action.



    The ratio of max to min spring length is maybe 1.5 : 1? In a pistol magazin, the ratio is much bigger, maybe 5 : 1?

    I did not measure the numbers, just guessed them, just want to give the idea.

    If you put always only 1 round in the mag, then it will survive much more cycles. Probably for example a 15 round magazine will also live longer (more cycles), if you put all 15 rounds in it and always load it to full capacity after firing only 1 shot.
    Last edited by P30; 10-20-2020 at 03:36 PM.

  8. #8
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    All of these are valid points but also help explain why mini gun companies for Mount Magazine production to specialists.

  9. #9
    Hobbyist JAD's Avatar
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    Over cycled springs break; they don’t relax. Relaxation happens because of stress; that can be on a curve of time over temperature or time over stress, but it’s always a function of time. Gun springs in general are always over stressed by design, because lots of force and travel are good and a 5000 cycle maintenance interval is acceptable. In applications where springs need to deliver millions of cycles, you get less force and less travel.

  10. #10
    Quote Originally Posted by HCM View Post
    All of these are valid points but also help explain why mini gun companies for Mount Magazine production to specialists.
    Er, what?

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