Hey Guys,
For what it's worth, Reloder 15 is the powder that Lake City is currently using in the military's M118LR Match ammo, under a Sierra 175 HPBT, Lake City case (obviously) and a No. 43 primer. Instrumental velocity is 2,580 @ 78 ft, which will keep this bullet supersonic out to 1,000, no problem. Varget is another excellent choice here, good velocities and outstanding accuracy. Beyond these, there's still no flys on the old standby, 4895. Give 'em a whirl, and you can't really go wrong with any of these for this particular weight range (168-175 grains).
As for the original question here, that 1x12" twist is pretty much standard fro the 308 Win, and will do a wonderful job with just about anything you'll want to run through it, up to and including a 190 VLD.
Kevin Thomas
Berger Bullets