If you have several of the same magazines, try switching the follower and spring from one that works into the one that doesn't work and vice-versa.  This may help to diagnose if its possibly the magazine spring, follower, combination of both, or if its a bad magazine body.  What we teach in armorer courses is that magazines are disposable, if they work use them, if they don't then you can try to switch the followers and springs, but if that doesn't work then they get tossed in the trash.


CY6  
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

Would help to know the brand of mag, hence a cheap clean or a know name brand mag that should be working.  Also, is this a M-14 converted mag (read mag lips may need to be tweaked), or a later AR-10 specific mag instead.


Ditto on pulling the mag down for a good CLP cleaning, then doing a quick diagnostic on the make to make sure that its recovering correctly.


With the mag pulled and CLP cleaned, the follower give a once over and skirt burs/ molding lines clean up, load three round in the to mag, then start checking the recovery of the mag.  To check, start by pushing the round stack down by the front of the round and let the round stack snap back up on its own, then push the rounds down from the rim and let them snap back up on there own.  In both tests, the round stack should snap back up so the top round is evenly against the bottom of the mag lip.

If you find that that either the rear of top round, or back of top round will not come up against the the feed lip on the snap up recovery, then the mag spring is not applying even tension across the follower to allow this to happen (more pressure on either the back or front of the follower).

To correct this, pull the mag apart again, and with the follower and spring in hand, you want to tweak the first spring coil wind where the mag spring is staring it's first wind downward from the bottom of the follower.  Two needle nose pliers works best, and depending on what part of the follower needs more upward tension (front or back), will tell you if you are bending that first wind coil more open, or more closed.

Pull it apart, CLP clean it, then with it back together, check the stack tension on the spring/follower via stake push down front and back, and snap back up recover.  Once you do with three round, then do it with 4 to check the other feed lip side.