I was referring to all 30 caliber rounds in general when I typed 7.62mm, I shouldn't have been so specific.
The Garand is a good example of a 30 caliber round being used very effectively in a semi-automatic weapon.
I have my doubts that any weapon without a mount can be fired effectively in fully-automatic mode. Whether its 7.62mm in the M-14, or 5.56mm in the M-16, I've never heard anything positive about fully automatic fire, unless its from a bipoded/tripoded/mounted machine gun.