OK, I'm going to be lazy and ask first before I thoroughly investigate the problem. I gave a buddy a G21 magazine (he and I have identical G21sf w/ ambi mag releases) and it worked once then failed to lock into the gun and fell out, with or without rounds in the mag. At first I thought the mag release was broken, but when we put in another mag that one worked fine the rest of the day. I believe the bad mag is an old version (has a square rear not angled) - is it a failure of the mag or just the wrong generation, or what? Thanks in advance for any comments.