I will toss in my advice. please no hate mail. I built a 270 variant of the 7MM rem mag and the load data was virtually identical to the 7MM. the best powders for me were the slowest ones. I got to the point that the range of 1.2 to 0.8 grains below max gave me the fastest and the most accurate hunting loads. I had a 1:8" barrel twist and was launching 140 and 160 grain slugs for Elk. The 120 grain Barnes X were also very accurate at 1.5 to 0.4 grains below max loads( RL-22 seemed to work the best) for deer. these are the powders I used and found to be accurate with the 140 through 160 grain 270 slugs: H-1000, RL-25, IMR-4831, H-4831SSC. I have lost my data sheet/pet loads for the rifle, along with the rifle itself. but I have the book I used to work up loads and it has notes all over it for what I found. nothing about the final loads for the gun because I had not gotten that far before the gun was lost.
I hope this will help.