Who in the world would be shooting at big game with a .45-70 out to 400 yds. This is a post Civil War carbine caliber. No stretch of the imagination would call this a flat shooting caliber. It's more like an inverted "U" !

Look at your charts. A .45-70 405 gr soft point at 400 yds is 918 ft./sec (slow), 758 ft/lbs of energy. If it were zeroed at 100 yds, at 400 yds it would be 170 inches below zero point of aim!! Thats over 14 ft. of drop! You'd never kill a big game or much else at that distance with this caliber.

Better look for a .300 WM, 7 mm mag or other rifle that actually can carry that far with a reasonable probability with practice could hit a paper target at 400 yds. Then let that trophy animal youshould show some respect to pass on by rather than take some wild shot with a caliber from the 19th century.