The .338-378 Weatherby Magnum is one of the most powerful production .338-caliber cartridges available, formed by necking down the enormous .378 Weatherby Magnum case. It delivers .338-caliber bullets at velocities significantly exceeding the .338 Lapua Magnum, generating over 7,000 ft-lbs of muzzle energy with 200-grain bullets. The cartridge is chambered exclusively in the Weatherby Mark V action — the only commercial rifle with a bolt face large enough to accommodate the .378 parent case.
Type: Rifle
Introduced: 1998, United States
Parent case: .378 Weatherby Magnum
Standardization: SAAMI
Bullet diameter: 0.338" (8.59 mm)
Case length: 2.908" (73.86 mm)
Overall length: 3.648" (92.66 mm)
Max pressure: 62,000 PSI
Rim type: Belted
Primer: Large Rifle Magnum
Typical twist rate: 1:10
Muzzle velocity: 2900–3250 fps
Muzzle energy: 3732–7041 ft-lbs
Effective range: 600 yd
Common bullet weights: 200, 225, 250, 300 gr
Primary use: hunting_large_game, hunting_dangerous_game, long_range_hunting
Production status: Active
Also known as: 338-378 Weatherby · .338-378 WM
History: Developed by Weatherby as part of their tradition of extreme high-velocity cartridges. The .338-378 was initially a wildcat embraced by hunters seeking maximum .338-caliber performance before Weatherby standardized it in 1998. It targets dangerous game hunters who want the penetration and sectional density of .338-caliber bullets with velocity approaching .378 Weatherby levels. Recoil is extreme…
Notable firearms: Weatherby Mark V