RE: what powder?
As several people have stated, 777 - (2F is what I am shooting) works great. I just returned from an elk hunt and, while it was only about a 65 yard shot, I smacked a nice 5x5 in the lung area and he side stepped twice, and tipped over like a ton of bricks.
I was holding good groups with 100 grains of this stuff and 348 gr Aerotips out to 150 yard in a .50 caliber.