I think it would still be a formidable weapon in the hands of someone who knew how to use it. The M16A2 has a 30 round mag which seem like a decisive advantage but if you were for example, a resistance soldier fighting against a tyranical government, you would likely be engaging troops from as far away as possible and you, very likely, would be firing no more than 8 rds before breaking contact and moving to a new position. Ammo availability is worth considering as well. We have seen how fast the NATO rounds can disapear from the shelves but, throughout all of that, rounds like .270, .243, 22-250, and 30/06 remained available.
Yup yup. Boom boom. We gone.
I believe that there is room for both the M14 and the M16 in the U.S. arsenal. The M16 was designed for more in close fighting while the M14 is better at the longer distances and is still preferred by marksmen (snipers) for that ability.
The U.S. has machine guns utilizing the NATO 7.62 rounds because of their greater range, accuracy and stopping power.
Unfortunately, the military favored the M16 for it’s lighter weight of both the rifle and the ammo with the lighter and smaller ammo allowing the soldier to carry more of it. On the other hand, the smaller and lighter ammo just doesn’t have the stopping power of the larger and heavier 7.62 round.
During the Viet Nam war I believe that it was the larger 7.62 round which had a variation which contained two projectiles within the cartridge which when fired not only sent two projectiles down range but also caused the leading round if not both to tumble which gave the weapon much greater effect to the degree that it was capable of completely severing an arm completely.
I suggest the following links for much better info:
http://www.paperlessarchives.com/vw_m16.html
http://m14forum.com/ammunition/52047-duplex-round.html