Haven't we all had to run around in the late 20 rounds with no freaking ammo? Hear the characters say " Getting light, need the juice" or "No ammo is no good!". Just make an Ammo Box, make it cost a certain amount based on what gun you have and whether it is PAP or not.
We havent needed an "ammo box" in any other CoD so why put one in now? Besides I can picutre a roll in of complaints when people start camping near the ammo box and kill farming people who are trying to reload. I cant really see the benefit to this idea.