Never reloaded the 7.62 X39, but in my experience, the 4895 series of powders, that is H4895/AA2495/IMR 4895 is one of the most flexible rifle powders on the market. It is best in middle sized cases. It was the IMR powder used during WW2 for 30-06 ammunition. The 7.62 Nato was developed with this powder before the Army went ball powder. I have used it in the 30-30, 30-06, 223. It should do just fine in the 7.62 X 54R and the 8mm Mauser.