Please OWI... this is possible in PR already since a decade or so... What's the point of playing insurgent team in insurgency mode if not to grab ammunition from the weapons cache?
Uhhmmm you can? What you are talking about? Go up to it and click whatever you need, or you can do rearm all but it'll eat your teams cost of ammo more.
What are you doing worrying about a game mode that has been dead in the water for years? Until the insurgency overhaul is back on the roadmap why waste your time?