Hi Jesse;
.308(7.62X51MM) is a very easy on the arm round compared to the magnums. Accuracy is great...plus the military has a lot of it

But both the .300WM and the 7mm Mag are in use with SOFs currently. The M24, M86 and some limited SOF only rifles are chambered for them. Under developement is a 7mm sniper specific round being tested in the M24TC(Titanium,Composite), the round is based on the Remington 7mm Ultra Mag. In the HTI/SNIPER area the .408 Cheye Tac is being tested to take the place of the .338 Lapua(the .408 CT can hold a better payload than the .338 for HTI).
In actuallity, the .308 earned the right from being very accurate, easy on the barrel,a standard military round at the time sniping came back into "vogue", and low recoil(back on target quicker).
Take care...Jim