I shoot a 6.5-284 Phoenix 1 in 9 twist with 140 Bergers. I'm getting between 1/2" and 3/4" groups. According to Berger 1 in 8 would be better! I've taken an antelope and an elk in the past two years. Both with one shot right at 300 yards. The elk stumbled 2 steps and dropped. I stay closer to 1/2" groups with 142 SMKs and H4831 but the 59 grains of Retumbo and Bergers put me at 3050 fps and I wanted that for the elk. It looks like I'll be taking it back to Wy for trophy mulie this year for the trifecta!
Good luck gun)