RE: 338 Win Mag
Using Weatherby Ammo a 200 gr. Nosler Partition in the .300 Wby. Mag. @ 400 yds. has a Velocity of 2308 f/s, and 2366 ft/lb of energy.
Using Federal Ammo a 210 gr. Nosler Partition in the .338 Win. Mag. @ 400 yds. has a Velocity of 1980 f/s, and 1835 ft/lb of energy.
Good luck.