Help! I just picked up a number of Glock mags (all used, for G22), but most of them refuse to drop free. They are marked LE/Military only. Any ideas on what I can do to make them drop? Since these are for range use only (I have reliable dropping mags for EDC), it doesn't bother me a bit to modify, sand, etc., but don't want to reinvent the wheel if somebody already has thoughts on this. Thanks a lot!