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AR15 Mags

Discussion in 'Black Rifle Forum' started by captdreifus, Jan 2, 2010.

  1. captdreifus

    captdreifus aSun666

    Jul 24, 2008
    Tempe, Arizona
    I know this has been brought up several times to the point of jambog, but I have a question. How long can you keep a USGI mag loaded without failures? I know its the compression/decompression that makes the springs weak, but how long have you guys kept your mags loaded for and have them still be reliable? I tried to search function but my search-fu is not so sharp at 0229. Thanks

  2. PlasticGuy


    Jul 10, 2000
    There is no established number. After a long time, the spring will eventually take set. How fast that happens varies based on how many rounds it is loaded with, and how the spring was made. Exactly when that will start to cause malfunction is dependant on the cyclic rate of your particular rifle, which is dependant on whether you have a carbine/mid-length/rifle, what buffer you're using, what ammo you're using, and several other factors.

    That is why it's a good idea to rotate out your defensive ammo every 6-12 months. Not only does it give you fresh ammo, it also checks to make sure the magazines haven't fatigued enough to compromise function.

  3. RMTactical

    RMTactical CLM

    Oct 7, 2000
    Behind an AR-15
    Pretty much, as long as the ammo is good for (which can be a long time if stored in proper conditions). I have had AR15 mags loaded for years and shot fine when I ran them.
  4. FatBoy

    FatBoy Millennium Member

    Sep 2, 1999
    Who knows is the correct answer, but I have a couple of AR mags that have been loaded and only unloaded while at the range for a number of years (7-8 years), and while not what you asked, I have a few Glock mags loaded since '99-2000 and two HK P7M13 mags that have been loaded and only unloaded while at the range since '89. The above mags haven't been "run hard", as I have other mags too, but they still function each time I take them to the range. This topic comes up all the time, so I have been doing my own little "test". While this is not anywhere near enough mags to draw any kind of conclusion, it is what it is. YMMV

  5. DScottHewitt

    DScottHewitt EMT-B

    Jul 4, 2000
    Waynesboro, VA

    Someone supposedly found a couple that had been loaded 25+ years earlier at Khe Sahn or somewhere. No problems.
  6. tebklr


    Mar 3, 2007
    ...pretty much until Hell freezes over. It's cycling that fatigues correctly designed springs, not a constant load.
  7. Alaskapopo

    Alaskapopo NRA ENDOWMENT

    Feb 6, 2000
    You know I have been told that but I have not found it to be true in my own personal experience. For example When I was forced to carry a Glock 21 the mag springs would go bad and stop locking the slide back after about 6 months to a year of being left loaded without cycling them. On the other hand magazines I use for competition that I load before the match and unload after seem to last much longer (2 years or more) before needed replaced depending on the magazine type. I think the amount of compression matters a lot too. I was once told that the last 10% of compression on a spring accounts for 90% of the wear. Basically if you download your mag springs will last a lot longer. I have found that to be the case in my own personal experience.
  8. MrMurphy

    MrMurphy ********* Moderator Moderator Millennium Member Lifetime Member

    Jan 16, 2001
    Buried in the X-files
    Fully loading a USGI mag will eventually cause some spreading of the magazine lips. Downloading to 28 or in some cases 26 for long term storage is generally recommended.

    We had magazines stored in our armory's war reserve stocks that were loaded and had been so for at least 10-15 years. Aside from drawing them for occasional exercises, where most still sat in the pouches, and none were fired the magazines were in good shape. No noticeable wear and tear, the occasional unload of the magazine to check for tampering, etc did not show any mags taking a set.
  9. captdreifus

    captdreifus aSun666

    Jul 24, 2008
    Tempe, Arizona
    thanks guys, I think I will reduce the mags I have for TEOTWAWKI/SHTF scenarios to 28 rounds each. I will fully load three and keep another 3 loaded with 28 and check for wear in a couple of years:) I'll report back then.

  10. lawman800

    lawman800 Juris Glocktor

    I keep my USGI mags downloaded to 29 and left them there for a few years... (I think at least close to 10 years or so... give or take a year or two) and took them out and unloaded them rapid fire without problems.
  11. HogGlocker

    HogGlocker Owner Since 88'

    I left several [between 5-8] USGI 30 rounders loaded to capacity once for about 5 years.

    Each functioned normally when fired....and I still use the same mags today.
  12. tebklr


    Mar 3, 2007

    Pat -- Very much appreciate your experience.

    I tried to be careful in my response, but perhaps I didn't stress "correctly designed spring" enough. I know not how Glock and USGI magazine makers design springs, but there is a ton of information available on spring design. My design experience is limited to cylindrical coil springs using constant diameter wire...the simplest of all springs, and not at all what is inside most firearms magazines. That said, the design parameters for any spring include, sping rate, required preload, maximum force at full compression (in most cases), maximum tolerable shear stress (this will predict fatigue life), and the wire diameter and material to accomplish it all. Of course, higher shear stress requires "better" spring wire, which costs more money. It's a balancing act.

    The springs I designed were critical to function, and could result in a serious injury if they failed. I was very conservative on allowable shear stress to ensure essentially unlimited fatigue life while using a standard material and processes. Fortunately, I had some available space to allow the spring to "grow" a bit. Magazine and firearms manufacturers may not have this space (prior, maybe poor, design decisions) and may have to run their springs with a lower factor of safety.

    You mention "the amount of compression". Yes, this is very important, as a one-time overload on any spring (correctly designed or not), will reduce it's ability to provide the desired force/displacement curve.

    Hope this isn't more of a response than called for or cared for.

    All the best, Tom
    Last edited: Jan 3, 2010