Primary weapons in Modern Warfare 3 can be customized with different proficiencies that give additional benefits. You can only have one proficiency equipped per weapon at any time.
By using a weapon, you level it up and at the same time unlock new proficiencies that you can use with it.
Reduces weapon recoil.
Increases bullet penetration. This works just like the FMJ attachment in MW2.
Allows two attachments to be added to the weapon.
Reduces flinching when you get shot by the enemy.
Increases your speed when you have the weapon equipped. This only works with Light Machine Guns and Sniper Rifles.
Allows you to steady your weapon by holding your breath for a limited time.
Reduces weapon sway when aiming.
Increases the weapon's range. Doesn't work with Light Machine Guns or Sniper Rifles.
Faster melee, but only works with Sub Machine Guns.
Increases damage. Shotguns only.
COD: Modern Warfare 3
Xbox 360, PlayStation 3 and PC. Multiplayer is available on Xbox LIVE (Xbox 360), PSN (PS3) and Steam. Xbox LIVE requires Gold Membership.
Call of Duty: Black Ops 3
Call of Duty: Black Ops 3 is the direct sequel to Black Ops 2. The game features new weapons, perks, scorestreaks, mp maps, and more. You can read more about call of duty bo3 here and get the latest updates. COD: BO3 will be released on the Xbox 360, One, PS3, PS4 and PC.