The .338-378 Weatherby Magnum

By Chuck Hawks

As the name implies, Weatherby's ultimate .338 is based on a necked-down .378 Weatherby Magnum case. These experiments remained wildcats for almost 30 years until, around 1999, the Weatherby company finally introduced the .338-378 Weatherby Magnum as a commercial cartridge. The .338-378 shoots a little flatter than the .340 Wby. Magnum, but in practical killing power there is little difference. Actually, the .338 Win. Mag. achieves about all the performance practical from a .338 hunting cartridge and the larger capacity .338 magnums are largely superfluous, even for Alaskan brown bear. They do kick harder, though!

Factory loaded ammunition is available from Weatherby with 200 grain, 225 grain, and 250 grain spitzer bullets. The 250 grain bullet is the popular Nosler Partition. The MV of this load is 3060 fps and the ME is 5197 ft. lbs. The 400 yard figures are 2297 fps and 2927 ft. lbs. Weather ballistics are as follows: +3.5" at 100 yards, +4.2" at 200 yards, 0 at 300 yards, -9.8" at 400 yards, and -26.4" at 500 yards.

Handloaders can come pretty close to these velocities. The fifth edition of the Hornady Handbook of Cartridge Reloading shows that 85.8 grains of H1000 powder behind a 250 grain bullet yields a MV of 2500 fps, and 107.8 grains of H1000 pushes the MV to 3000 fps. The maximum H1000 load in the Nosler Reloading Guide is very similar. The "Rifle Trajectory Table" shows that a 250 grain bullet with a BC of .473 at 3000 fps has a maximum point blank range (+/- 3") of 297 yards. The Optimum Game Weight Formula shows that a 250 grain .338 bullet at a MV of 3000 fps has an optimum game weight of 1100 pounds at 400 yards.

Note: A complete article about the .338-378 Wby. Mag. can be found on the Rifle Cartridge Page.

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Copyright 2004, 2016 by Chuck Hawks. All rights reserved.