Cache some cases of ammo from your old stash NOW. That stuff never gets messed with until the ammo supply situation improves or you start combat operations.

If you circulate through a couple of combat loads of ammo without obtaining more, then you either picked the wrong types of combat operations, ended up dead, or got really retarded about the concept of obtaining supplies form enemy personnel and supply points.

What could be a problem though is the diminishing returns on the amount of ammo you expend vs the amount of ammo you obtain when you take down enemy personnel.