put some rounds through my MK 2 a few weeks ago. two mags were OEM and two were aftermarket. I cleaned them all fully, took them apart, went over them, lightly - really lightly, oiled all the pieces and put them all back together. The two Ruger mags worked perfect. The two aftermarket mags were like 50% fail to feed right out of the gate, just terrible. I was thinking of giving them a look to see if there was something that could be remedied before relegating the two failure magazines, to the bottom of the box of stuff that will never get looked at again and forgotten about. I've never had magazines just fail before. Nothing looked wrong about them, springs seemed like the ones in the OEM magazines. They don't seem mechanically complicated in their job, so - what can make them perform that terrible?