I got this load from the late Jack Carter, founder of Trophy Bonded Bullets. He was a fan of the 416 Hoffman, and I had one built shortly before Remington announced their version of the 416. Here's Jack's load, which as he told me "Is one hell of a killing machine".

400 grain Trophy Bonded Bearclaw or Sledgehammer solid.
81 grains of Reloader 15
Federal 215M Magnum primer.

Using Jack's load, I get 2,510 fps out of my rifle. It's one heck of a cape buffalo killing load.