I poked around on this a little, because I'll probably give that mode a shot someday:
If... you are slightly holding down R when reloading then you will switch to military rounds and its almost impossible to tell if you are playing on Ranger/hardcore.
...
If the problem persists the only way I can see to guarantee that you don't use military rounds is to use a non-assault rifle weapon.
Do you mean how do you tell which ones your'e using in the gun? If so I think if you tap the reload button it will us dirty ammo, but if you hold the reload button it will use military grade ammo. But in Ranger there's no way of see how much of each ammo you have other than at trade depots.
Ya I figured as much. Was seeing if there was a way to inspect the gun to see for sure.