Vihtavuori answered to my questions and were again very helpful. They suggest, with a Sierra RN 85 grains (.308) :
2,8 grains N-310, Vo +/- 1100 f/s = starting load
3,5 grains N-310, Vo +/- 1200 f/s) = maximum load
or
3,7 grains N-320, Vo +/- 1200 f/s = starting load
4,3 grains N-320, Vo +/- 1300 f/s = maximum load
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