I bought an ammo can that will fit a row of five upright standing 30 rd magazines side by side with room to spare. If I stagger the configuration however, (#1: follower facing up, #2: floorplate facing up, #3: follower facing up...) I can fit six snugly. What I was wondering was if the USGI mag body was designed perfectly parallel || or if there was a slight taper to them \/ (a little exaggerated there )at the feedlips. Whatever the answer is, all of my mags drop free (or were "corrected" beforehand)

I think it's more a factor of the overtravel stop below the mag catch hole than any taper to the body. If you stagger them floorplate, follower, floorplate, follower the extra width of the stop is averaged out. If you stack them all floorplate up or floorplate down the extra width accumulates.

Good point, tweak.