There's differing ways to define a 'machine gun' in gun terminology, none really official, or particularly consistant. Generally, pistol caliber full auto's are referred to as sub machine guns, rifle caliber dedicated full auto's as machine guns (sometimes light machine guns), select fire (full or semi auto from the same gun) rifle caliber as 'assault rifles', larger than rifle caliber but smaller than cannon are sometimes called heavy machine guns, and at some point (I'm not sure what caliber designation, definitely by 20mm) they become automatic cannon. Legally, anything that fires more than one shot with a single pull of the trigger is a 'machine gun'.
They have pistol calibers as submachine guns, but they list the m4, ak47, steyr aug, and colt commando as automatic rifles. The only gun they list as a machine gun is is the m60.
Seeing as i have already wasted way too much of my life playing that stupid game, i think from now on i will go with their terminology.