I recently learned of the weapon proficiency feature when I was playing through the half life 2 maps using these weapons, as I tend to overlook parts of the features list when initially installing weapon packs of this type, and I would like to know if anyone has any idea how you actually obtain weapon proficiency (After a certain number of kills you get it, after a certain number of reloads, etc.) and if so how long would it take to get weapon proficiency for a weapon?

I think it's quite an interesting idea, since it changes the reload animations, but it would be nice to know if firing shots and reloading continuously is a waste of time or spawning hundreds of enemies to slaughter has nothing to do with it.