Received 2 full size M&P 9's. One is MPF and the other is MPM in the SN. The MPF came with black follower magazines and the MPM came with gray follower mags.
 The MPF was made Julian date 6220 and the MPM was made Julian 7012.
 Anything I should know about these two genres?

Thanks!

There have been two revisions to the M&P pistol. Revision M and Revision N. Both of your guns are new enough to be Revision N. If you field strip the pistol and look inside the dust cover you will see "REV N".

The gray followers are newer than the black and supposedly more reliable. So if you were to put gray followers in your other gun they would be equal. Personally I have never had any problems with the black followers.

http://mp-pistol.com/boards/viewtopic.php?t=1032

Thank YOU, Gary!