In this day and age of modern sniper rifles, the .308 projectile is almost archaic.
Modern long rang projectiles with impressive ballistic co-efficients, rifles, and optics make shooting at 1000 yards (a true feat with a .308 rifle) boringly easy.
For me, nothing illustrates this quick like the dramatic difference in wind calls: even a slight breeze on the check requires a calculated adjustment at distances with a .308. With a modern projectile, you can pretty much just ignore it and the long, sleek, aerodynamic projectile glide through the air.
It is unfortunate that the realities of interservice rivalries/politics prevent the USMC from getting the best weapons they need, but it is what it is.