It's not the mags, it's the angle of the gun and the way you hit. For lefties there is a better way though, as the bump method will always bite you in the ass. Drop your trigger finger on top of the mag release, not pushing it down, but also not just floating. When you slap a mag in and feel it seat, most likely the gun will move up and your finger will stay in place triggering the slide, or worst case, you press down with your trigger finger. Snootworks does faster mag changes than me many times because of him being a lefty