I used Varget (ADI 2208) in the 416 Weatherby with 400 grain Hornadies and from memory used 90 grains. It was very accurate and pressures were mild.

The pressure would be a bit higher in a 416 Rigby with the same load because the case is a little smaller and the 416 Wby has slightly more freebore.

You can get suprising levels of accuracy from the powders in the Varget/4064/4895 burn rate in these big cases.

In my kast 460 Wby 85 grains of IMR 4064 and 500 grain Hornadies did just over 2000 f/s and with excellent accuracy. Pressure extremely mild considering a top load with 4064 is in the 104 to 106 grain area with 500s.

No fillers were used

Mike