Ahhhh - Varget- That should work.
Here's a quote from a forum I found.

"Latest update on my .416 Ruger: now using 350 grain TSX bullets with 80 grains Varget and 215 federal primers. This load shows no signs of high pressure, and puts bullets in EXACTLY the same place at 50 and 100 yards as Hornady DGX and DGS 400 grain bullets. I plan to try it on Leopard and Bushbuck this year in Zimbabwe."

On Nosler's site, they went from 66.0gr. Varget to 70gr. Varget with 400gr. bullets and the top speed was from 1,100fps to just under 2,300fps. Reloader 15 did better with the 400's on the Nosler site.

here's another quote

"I did some more shooting with the 416 Ruger on Sunday. When I reached 78.5 grains of W748, the bolt did seem a little sticky, although the primers were fine and case head expansion was minimal. The velocity was an average of 2365 fps, equating to 4967 ft/lbs of energy with a 400 grain A-Frame. Not bad for a 20 inch barrel.

I think I will load some more at this charge and do a little more rigorous accuracy testing before I settle on this load.

This would be a tough load to beat for big Alaskan browns and moose. Now, if I can only quit buying guns for a while and put some money away for that trip!!"