Twitter / JoeCecot: @ElliotSpeller @CODINT3L ...
Joe is a Multiplayer Designer at IW so we can take this to be true.
Turns out all SMG's except for the the Mtar received a minimum damage range buff and the Bizon and Cbj have a max damage range buff.
I wonder if this has anything to do with all the pros suddenly finding the vector a melt machine and actually using it over the mtar in a lot of situations.