Gak ... must be having a brain-dead morning (need more coffee lol), as this was supposed to be a response to this thread's discussion and not a separate post...
The M16/AR15 was initially licensed by Armalite -- a subdivision or subsidiary of Colt (or was that later -- feeling too tired at the moment to go research).
All models of the AR15/M16 use 5.55mm ammunition, available in ball (common round) and tracer.
The differences between models (up to the current version) were very minor and cosmetic ... the A2 does have burst selector mode, whereas previous models did not.
Too bad 1967 was too early for my personal favorite, the M16/203. Oh well ... perhaps in the sequel.
Too bad the game limits you to one main weapon, as it was not uncommon to sling the M79 to hang in front of your chest with a buckshot round loaded (for those nasty close-in ambushes), while still carrying an M16. Though the original TO&E (Table of Organization and Equipment) for a 79 gunner was the 79 and a .45 pistol. An FYI -- the M79 had HE (High Explosive, Starshell, buckshot and CS as munition types).
Take point troop and don't get yourself waxed to the max. Geronimo. -- d2