Interesting Galenical, because I didn't even know what was the separation between machine gun versus submachine gun.....Pistol ammo is the determing factor of what is or is not a submachine gun.
Interesting that an Colt M4 is not considered a submachine gun in the 5.56 round, until you chamber it in the 9mm parabellum round. Then it is reclassified.
Good catch. :-)