Well, what I find very interesting is the difference between CARTRIDGE, 9 MM, BALL on p. 12-3, and CARTRIDGE, 9 MM, BALL, NATO, M882 starting on p. 12-5.
The former is specified only for the "Modified M3 Submachine Gun or commercial weapons," and not authorized for the M9 pistol.
I assume this was for the M9, and for a bunch of foreign/allied pistols and submachine guns. Greater muzzle velocity than the other one.
Why? I've never heard of a "modified M3 SMG." We had still had M3A1's with our tanks in the late 1970s -- but that shouldn't be what they're talking about, is it?