My best shot groups with IMR4064 w/Winchster primers and federal cases came using 34.1 grains @2900fps. However I've switched to Varget for the same reason, it's not temp sensitive. I also use Varget in my .223. My Varget load came out @ 36.9 @ 2975fps. Both the Imr4064 and Varget loads are in a Mod 12 VLP DBM in .243.