IMO a 308 isn’t necessary; 5.56 ammo weighs so much less, and the magazines hold more, and the guns are lighter.
Was anyone asking about 5.56? God knows we don't need another 5.56 vs. 7.62 thread. That horse is so beat it's not even amusing anymore. Sounds like the OP wants .308 not sure if he cares if it is necessary or not.