Would be nice to be able to store partial mags instead of wasting them or leaving a 1 or 2 round mag still in the gun.

Basically instead of a magazine pool you have a bullet pool like in other FPS games. All magazines grabbed from the backpack will be fresh mags and when you're down to the last few bullets the last magazine you grab will have the rest of the bullets in it assuming it's less than the magazine's capacity.