This developer diary for Modern Warfare 3 discusses the changes that have been made to the progression system. Leveling now extends to individual weapons, and going a step further, players can further customize their firearms with proficiencies that can alter kickback, melee speed, and more.
Internet-based discussion can only be civil in this post-Battlefield 3, pre-Modern Warfare 3 period. If I say that phrase three times in front of a mirror, maybe it will come true. If not, my backup plan is to call upon the Candyman.
This 2015 D.I.C.E. Summit talk explains the entire history of Call of Duty's zombie mode
10:30 AM on 02.12.2015
Call of Duty unleashes DLC, zombie horde on PlayStation and PC in late February
5:00 PM on 02.04.2015