“Unless you are in Afghanistan with long and open ranges and mountains.”
Under the conditions described above the 7.62MM/.308 Winchester is needed. The newer AR10 rifle versions weigh within a pound(unloaded) greater than the weight of the AR16/M4. The effective range and knockdown power of the 7.62X51 NATO is much greater than that the 5.56 round.
Yes M25s, M110s, and even M-14s that were taken out of mothballs.