Are you suggesting that guns have bullets in their "chambers" when you unload weapons? It sort of sounds like you want to add micromanagement of ammo just for the sake of realism. It doesn't really sound fun.
If you're suggesting a mechanic to help you conserve ammo, the game already "collects" non-empty magazines to make full ones. If three guns fire one bullet each, you don't lose 3 magazines, just 1 (not perfect, but perfect would be overkill).
On your engineering suggesting, I feel like soldiers would be more than able to fill their magazines with ammunition between missions.
Sorry to poop all over your suggestions!