Congrats on a fine rifle, I have hunted with a 6.5x55 for nearly 35 years, built over 100 of them as gunsmith the last 35+years. I have done extensive load development, trial and error, and using Qwik load software. The one powder that stands above all, is IMR 3031. I have loads that shoot around .300 groups at 100yds, with 85, 120, and 140gr bullets. Pm me if interested, will save you a lot of trial and error. I took my longest shot on a deer this past season, at 510 yds, angled forward, with a 120 Sierra, running around 3000fps. The bullet entered between the last two ribs, angled forward thru the vitals, and blew thru the right front leg, nearly blowing it off.