MW3 isn't a vast one. Activision has made a handful of balance tweaks to weapons that include the Kastov 762 & 545, FJX Imperium, KV Broadside, and a handful of others. On the Zombies side of things,

Activision has issued an update for Call of Duty Warzone that nerfs a number of weapons that had come to dominate the meta. The highlight here is a nerf to the Kar98k after the iconic Call of Duty marksman rifle was added to the game in Season 4 and came to dominate battle royale just as it did Verdansk when Warzone launched.