I recently purchased a Glock 22 mag from my friend. On Labor day I went to the desert to try it out. And the mag works great except that when the last round is fired the slide does not lock back. Any info would be great!Oh one more thing the mag has a two round extension on it.

The follower does not have enough spring tension on it. Either get a Wolff +10% magazine spring or remove the +2 extension.

Thank you for the information once again the AR15 forum comes to the rescue!!!!

A worn follower could also cause this problem, not a bad idea to replace the follower while you are at it.

Or.......if you are right handed and have shot a 1911 style handgun for a good while and shot with your thumb high for ready access to the external thumb safety of the 1911 your thumb may be riding on the slide lock not allowing the slide lock to engage the slide.  I shot a 1911 for many years and I still shoot with my thumb high (do not want to change) my slide never locks to the rear, I just understand that and rack the slide.  Might not apply in your case though.

I had the same problem with my 22 mag.  The spring was not providing enough tension with the +2 extension.  I have also seen the polymer followers were a groove and no longer hold the catch.  New follower and spring should fix it. Now you know why your buddy got rid of the mag.