I use 78.0 grains of IMR4350 with 300 A-Frames, which gets around 2550 from the 22" barrel of my semi-custom Mark X Mauser, and sub-inch groups. I use 81.0 grains with 300 Partitions and Siiera GameKings in the same rifle, for just about the same muzzle velocity and accuracy, but A-Frames tend to produce somewhat more pressure, due to the pure copper jacket.
Have tried H4350, R15, Varget, Big Game and some other newer powders over the nearly three decades I've owned the rifle, but so far none has done as well as IMR4350. Have also tested the load at zero degrees Fahrenheit, and it only loses a few fps, probably because it's pretty compressed.
