The ammo pouch that costs approximately $290 is having issues when it's doubled up on one belt. If one looks at the image below, one will see what I mean:
The lower pouch's GUI makes it appear that one could fit in long magazines, but it never allows for them to be stored there. Rather, one can fit objects as long as they're no longer that 1 box in size. It operates exactly as the ammo pouch located above it, but one can't see the horizontal divider.
I also had some strangeness when attempting to "Fill Magazine." For the entirety of last night's game session, I could not see the ammo boxes in the large rectangle. No items where displayed within said rectangle, but one could float the mouse through that portion of the GUI, and see text descriptions appear, describing the invisible ammo box the mouse was floating over.
Today, the ammo boxes appear in the GUI without any problems. Weird!