IMR4895 is a perfect match for the .308 and 150 grain bullets. If somewhere between 44 to 46 grains doesn't shoot straight something is wrong with the rifle. It should give right around 2800 fps from a 22" barrel.
Do start lower, though. The Sierra manual tops out at 43.7 grains, Nosler at 44.5, Speer at 45 and Hornady at just over 46. I've run 46 grains with a Hornady 150 SP for years in three different Remington .308's with no problems and great accuracy.
