Given the fatigue system, with magazines that are near empty taking up as much space/weight as full ones, and the simple fact that a near-empty magazine is not useful, while bullets are a very valuable resource... there really needs to be an in-game way to combine partially spent magazines to make full (or more full, given what is available) magazines.

Even if it takes time to do, which prevents it from being used in combat safely, there are always lulls in the fighting where you'll find yourself with four half-empty mags you really wish were two full ones, and nothing to do about it, besides scavenge for fresh ones and throw away what you already had.