WaW's MP40 was definitely nasty, but it grew less consistent the further away your target was, CoD4's M16 pretty much dominated every possible range. With a RDS it was basically sniper rifle accurate, and could practically be used as a shotgun close range.
Don't know the name of the gun, but it's the second LMG in Black Ops 2. It has a super high fire rate and almost no recoil. I think it hold around a hundred bullets. I honestly feel cheap just mowing dudes down without having to reload. Slap on the scope that puts red squares over enemies, a quick aim grip, and whatever the thing is that increases accuracy and its all over. I set all my perks to whatever helps me get around fastest and I can move like I have an assault rifle. Really, I'm surprised more people haven't discovered this.