Weapon Level

Weapon Level is a feature introduced in Call of Duty: Modern Warfare 3. Each weapon has its own individual rank and in order to unlock available Camouflages, Attachments, Proficiencies and Challenges, the player must rank up the weapon by using it in combat. When the weapon is leveled up, additional customization options are unlocked, such as the reticule of the attachable sights, excluding the Hybrid Sight, HAMR Scope, and Thermal Scope. Max leveling a primary weapon will unlock Gold Camouflage for the said weapon, although the final level requires substantially more experience than prior levels. The final level is 31 for primary weapons, while for the secondary weapons it's 10. Not all weapons require the same amount of levels to obtain camouflages, attachments and the like. Launcher levels are implemented to add longevity to the weapons, as there are no attachments or camouflages for them. To gain the weapon title for primary weapons, the player must unlock the last attachment, even if it isn't level 31.

The order and level with which items are unlocked for primary weapons remains similar across all types of weapon:

Required XP
Every primary weapon, except for the Riot Shield, requires a set amount of XP to attain level 31.

Each secondary has a set amount of Weapon XP needed to attain level 10.

Trivia

 * The max weapon level was originally going to be 26 for primary weapons and 14 for secondaries.