I've found that IMR 7977 works great in my 7MM Rem Mag(Win. 70). Velocities(chronographed by me) and accuracy were both better than IMR7828(my former "go to" powder for 7mm) in my rifle pushing Barnes 140gr T-TSXs. Tried Reloader 26 to no avail.
IMR7977 produced 4 shots into 0.6" groups at 100yds; vel. = 3,100fps with none of the usual "high pressure" signs(heavy bolt lift, flat primers, shiny marks on the case head...). Not exactly temperature extremes but two different days on the range at 30 deg. and 60 deg. produced slightly under 0.6" and velocities were unchanged. I stopped there since accuracy was so good but probably could have pushed it a bit more(but why?).
Leftybolt
