The problem in the RPG is you don't have concepts (well, kind of, but it's a stretch) of suppressing fire, cover fire, etc., all of which can consume ammunition- in some cases vast amounts of ammo. You're also looking at an RPG where a single shot can kill 10 guys, and you're looking at a situation where in combat the PCs have an exaggerated likelihood of hitting their enemy targets.
If you base the RPG load out on real world numbers you’re going to very likely end up in a situation where you’re essentially giving the players unlimited ammo but requiring them to mark it off. That’s fine, but I think you’re missing a thematic part here, which is to either make your PCs think about ammo or to let them not have to worry about it.
Pick what theme you’re going for and disregard 21st century soldiers. FS, for my group, took 6 reloads for the tac and about 30 extra rounds for the dev, and FS is a loooong adventure. 10 magazines would've removed the ammo considerations from the players alltogether.