When I reload my gun, I want used magazine to go in inventory. I also want to be able to "open" it, like I open bags now, seeing every bullet inside in order. So, if there are bullets left, I can use it again, OR drag-and-drop any bullet from it to inventory/another magazine. I can load it to the gun of another type (but using same caliber). I can load different types of bullets in one magazine in some order (for example, load one tracer bullet after every three normal). It would take time, but if I have a lot of time and not much ammo (it happens often in arma 3) (or a magazine with same bullets but for different gun) I would not just throw away my partially used magazines but store them for using later.
That's not something critical, and I hope you're already planning something like that, just wanted to say that's what I really lacked in many games. It would add a lot of realism and be really useful.