To explain, the current setup is that you have a pile of rounds in inventory, and when you reload, you take some from your pile, and shove them in your gun. Your bullet pile decreases in size accordingly. And yet, the animation used is you taking a magazine out of a magazine well, and putting a new magazine in. Where do these magazines come from and where do they go? Why are they always full?
A more realistic approach would be to have interchangeable magazines based on ammo type and potentially some other factors about the weapon. So, 5.56mm magazines would be interchangeable between varmint rifle, service rifle, etc. and .308 magazines would be interchangeable between the few sniper rifles that use those rounds. So, reloading would take a magazine from inventory for that round type, and you fire the weapon, which removes rounds from the magazine. If you reload before your magazine is empty, you have a partially full magazine sitting in inventory. If its empty, you have an empty magazine sitting in inventory. You can't just take rounds from your pile, which you found on some dead guy - you have to put it in a magazine first (which you should be able to do in the field, but it shouldn't be so quick you could do it during combat). This means that in combat, reloading after firing just a round or two is a bad idea, because you end up with a lot of partial mags.
It would mean more prep required for assaulting enemy strongholds. It would mean that extended magazines would be a property of the magazines used rather than a particular mod on the weapon. It would make sense if you could make magazines (extended and regular) with the proper guns/repair knowledge.