In Call of Duty: Modern Warfare 3 for the PC, PS3, Wii, and Xbox 360, you can now level up specific weapons to gain proficiencies with that weapon.
You can only add one proficiency to a weapon at a time, and they can only be added to primary weapons, but this will still add some customization to your play style and possibly give you a little bit of an edge that you didn’t have before.
Here is the list of proficiencies, and which weapons they can apply to.
Attachments – Equip two attachments to your weapon (All weapons)
Breath – Hold breath when aiming down sights (Assault Rifles only)
Damage – Shells do more damage (Shotguns only)
Focus – Reduced flinch when shot (All weapons)
Impact – Better bullet penetration through walls (All weapons except SMG’s and Shotguns)
Kick – Reduced recoil (All weapons)
Melee – Faster melee swings (SMG’s and Riot Shield only)
Range – Increased range with weapon (SMG’s and Shotguns only)
Speed – Faster movement with weapon equipped (Light Machine Guns, Sniper Rifles, and Riot Shield only)
Stability – Reduced sway (All weapons)
