I have about 15 of them and I have done a little modifying to them they seem to stratch up the cases on the 9mm. I disassemble them and lightly file and round off the feed lips and take a box cutter or a razor and cut off any extra plastic up under the feed lips next to the follower and they have always worked great never had any malfunctions..when the spring goes weak I buy a spring which actually make it as reliable as a glock factory mag or ill toss the mag if they are online and available for cheap.