Having worn out a few 1:12 twist 7.62 NATO 24" barrels shooting bullet weights from 147 to 190 grains scoring well and winning some matches with them, it's my opinion that those bullet weights for bullets will drive pins (they're smaller than tacks) with the right load in good barrels 26" long. Many others have done the same thing.
Powders, many extruded (stick?) ones are suitable for the .308 Win in a 26" barrel for good accuracy. I'd not even try any ball powder if best accuracy's your objective. Too many top ranked competitors tried it over the years and none of it produced the consistant, excellent accuracy levels as extruded powders. Much consternation among competitors prevailed when Winchester put ball powder in M118 Match ammo while they operated Lake City Army Ammo Plant; it did not shoot all that well accuracy wise. Use powders from the following link:
http://www.hodgdon.com/burn-rate.html
... with a burning speed between that of numbers 77 through 100. Slower powders for heavier bullets, faster ones for lighter ones. Favorites in the heyday of .308's in various competition disciplines were IMR4895 or Varget for the 150 grain ones, IMR4064 for the 168 through 180's and IMR 4320 for the 180's and 190's.
If accuracy's important at very long ranges, muzzle velocity numbers have to be a concern. Not the average speed bullets leave at but the spread of the velocities. A 50 fps spread in muzzle velocity from a .308 will cause a 1/10th inch/MOA vertical shot spread on paper at 100 yards. At 1000 yards, the vertical spread will be 20 inches; 2 MOA. Slower bullets drop more than faster ones.