ntg,
I am loading IMR-7977 in both my 270 WSM and my 7mm Rem Mag with very good results. I have not loaded enough in my 270 Win to offer any advise, however I just received the Oct edition of Rifle's Handloader mag and found a article where IMR-7977 was used. This article was written by John Barsness and he used IMR-7977 in a 270 Win. . He was able to get 2816 ft/sec. using 150 grain Sp.out of a 22 inch barreled Winchester Model 70. His load was 60 grains of IMR-7977, Winchester cases, WLR primers loaded to a COL of 3.345. His accuracy was just over an inch for 5 shot groups.
I am going to try this load, working up of course in my 24 inch barreled 270 Win.. I have been very pleased with this powder in the two calibers that I have tried so far and I think it should work well in a 270 Win.