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.
In Call of Duty: Modern Warfare 3 primary weapons customized with these improvements called proficiencies that will give you additional benefits which you can use it in the game. Note that you can only have one proficiency equipped per weapon at any time.
Using the weapon together with the proficiency, it will also level up at the same time to unlock new proficiencies which can use it in the future.
Reduces weapon recoil
Increases bullet penetration. Works like a FMJ attachment in Modern Warfare 2.
This will allow you to add 2 attachments to the weapon.
Reduces flinching when got shot by the enemy.
With your weapon equipped with this proficiency, you have the increased speed. Only works on Light Machine Guns and Sniper Rifles.
Allows you to perform steady aim by holding your breath for a limited time.
Reduces the weapon sway when aiming.
Increases the attached weapon range. It won’t work on Light Machine Guns and Sniper Rifles.
Faster melee rate, only works on Sub Machine Guns.
Increases damage on shotguns, only.