Snowtrekker--RL-15 is one of the best if not the best powders for a 308. Now the fun side-Rifles are like women
.It;s not to say your's will like it,but it would definetly be my first powder choice I would try. I did mess with Varget a few times ,but with not very good results. As for the COL, Mess around there to.
Bart mentioned 4064 powder, I never tried 4064,might have to give that a shot this summer too.
Group size,,, I can pull 9 inch groups with an accasional flyer
. I jst started shooting 1000 yards last year,so if you ask me I will tell you that I have a lot to learn yet, The wind and mariage (sp) is the biggest factor i am dealing with now.
That load in my rifle ( Savage FVSS in a Dog Tracker Stock ) will do golf balls at 300 yards of a bench.
Good Luck and keep us posted