I wouldn't have thought of using Big Game, but obviously it works!
By the way, 100-grain Nosler Partitions in Weatherby factory loads regualrly shot in the 5/8" range in my rifle. The buys at Nosler tell me their test standards are the same for Partitions as any of their other bullets. I suspect one of the reasons some people don't get good accuracy out of Partitions is they don't expect it, so don't take the time to try different stuff, whether seating depth or different powders.
