Inch mags will not fit a metric upper (BIG lug on the front is too big), but metric mags will fit (a little loose but will still work) on an inch rifle. Otherwise, they should be identical (except for some differences in the floorplate also).
I don't have calipers or anything like precision measuring tools, but I do have both inch and metric mags and a ruler, so here goes:
max length of the mag feed opening (inside dimension, NOT counting the little tab cutout at the back for the hold-open) is 2-13/16".
Max width of the top mag opening at the widest point (inside dimension) is 25/32" The feed lips taper, but there is always a bit of "lip", so the top opening of the mag is always smaller than the max inside diameter of the mag width, which is 15/16".
These dimensions (within the accuracy of my plain jane steel ruler) apply to both inch and metric mags.
Hope this helps
