I know that the relative burn rate ranking of powders depends on many variables. Case to bore capacity ratios, pressure, etc. The first source I checked showed in close order from slow to fast Big Game, 2000-MR, R-15 and then a big jump to Varget. A second reference I just found shows in close order from slow to fast 2000-MR, R-15, Big Game and then a big jump to Varget. So maybe any of these first 3 powders could reach about the same velocity as Johns published Big Game loads with 286gr bullets.
I'll carefully push past the Nosler manual with the R-15 I ave watching very, VERY carefully for any signs of pressure.
