Although I do not see too many .308 Win rifles in our elk camps, the ones that I do see are almost invariably shooting 165 grain bullets. The .308 starts to tail off on velocity too much for most hunters when bullets heavier than the 165 are used. Some bullets (mono-metal, etc.) really like fairly high impact velocity to open reliably.
The bright side is that the 165 grain bullets at 2,750-2,800 fps are a very effective elk load. I have seen some very big body bulls taken with .308 rifles.