AR build problems with Magpul PMAGs

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  • jimbobborg

    Oddball caliber fan
    Aug 2, 2010
    17,124
    Northern Virginia
    I'm dusting off the cobwebs from my competition AR and decided to do some function tests. Prior to this, I have not run PMAGs through this rifle and it just worked.

    First function test, had failed to feed with all magazines and my reloads. I had two steel and on PMAG. After the RO lent me some CLP, it started working. Took it home and gave it a thorough cleaning, used Mobile 1 for lube.

    Second function test. I took this rifle and a new M4gery build with just PMAGs. Four PMAGs and all of them failed to feed right, even with Winchester 5.56 ammunition, through the competition rifle. I even had double-feeds :mad54: I tried the same mags and ammunition in my new build and it had no problems with the magazines.

    Ejection both times with the competition rifle was fine. I've put maybe 800 rounds through it. During the cleaning I shot Brake Cleaner through the gas tube, it came out the other end just fine. I'm testing this weekend with steel mags to see if it still likes those. Anyone else have problems with PMAGs on a build?

    The lower in question is a Spikes, with a CMMG LPK, Ergo F93 Pro stock with included receiver extension, standard carbine buffer and spring.
     

    F-Stop

    Ultimate Member
    Feb 16, 2009
    2,494
    Cecil County
    Did you try swapping the uppers around (As long as it doesn't break law) to see if it's feed ramps or something in comp rifle? May help narrow your focus.
     

    jimbobborg

    Oddball caliber fan
    Aug 2, 2010
    17,124
    Northern Virginia
    I had a similar problem: my lower receiver is out of spec. Rather than send the mags back, I filed down down the offending notch on the magazines. Could this be your problem? http://www.thefirearmblog.com/blog/2012/11/19/magpul-m3-pmag-compatibility-issues/

    No, the Spike's I have isn't a billet lower. The magazines work fine in the Bushmaster lower I just built. I'm going to switch uppers and parts next time I go to the range, and I'm bringing more ammunition since I only brought 90 rounds with me.
     

    Sticky

    Beware of Dog
    MDS Supporter
    Mar 16, 2013
    4,503
    AA Co
    Something is outta spec somewhere, that's odd. Swap about and see if you can narrow it down. Measure the location of the mag catch in the lower and compare to another that works. It sounds like the mag is not properly positioned. Usually if mine doesn't 'click' in, I get a fail to feed on dropping the bolt. Whack it on the base and hear the click, all is good.

    I have run pmag and others as well as steel in many of my builds and the only issue I have had was perhaps a fail to lock on the empty mag.

    That said, I know from milling magwells, that all mags vary. A lot! Even pmags, from one gen to the next can be dramatic and there is some give and take when milling a CNC lower, but a forged lower has nothing done to the magwell, that is in the forging. Usually this only results in issues with bolt catch and mag follower relationships, not failing to feed, nor double feeding.

    ETA: when you said reloads, it popped up a red flag, but when you tried factory ammo with the same result, it sounds like an issue with the weapon/mag relationship, not the reloads (and I do reload most all my ammo.. lol)
     

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