[Kartoffel]

In defense and delay I'll stack same type units without necessarily wanting a more experienced unit who uses ammunition at a faster rate taking ammo from a green unit who uses ammunition at a slower rate because I want the green unit to level up. This is but one example, my point is what if you don't want sharing ammo. As for realism I have to admit your suggestion is more realistic, who has ever watched a war movie and seen two same nation infantry sections refusing to share ammo when to do so could mean their demise.