I thought I had a winner with the Korean-made aftermarket mags sold on CDNN's website. They are metal 30-rounders that rock right into place for a good lock-up, but the springs are too weak to put all 30 rounds through. A guy can put stronger springs in (i.e. Wolff), but then the mags will not hold 30 rounds (27 maybe?), and the cost approaches that of a factory mag. Bottom line...go with factory mags, if they can be found...