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The Ultimate Reloading Manual
Wolfe Publishing Group
  • reloading manual
  • alliant reloading data
  • reloading brass
  • shotshell reloading
  • bullet reloading
The Ultimate Reloading Manual
hodgdon load data

.375 Weatherby Magnum (using Hornady bullets)

Author: Brian Pearce / Wolfe Publishing Co.
Date: May 30 2014

After developing the .270, .300, 7mm and .257 Weatherby Magnum cartridges, around 1944/45 Roy Weatherby developed his .375 Magnum. Based on the .375 H&H Magnum case with the shoulder blown out to increase case capacity and velocity, it proved capable of pushing a 270-grain bullet to 2,940 fps or a 300-grain to 2,800 fps, a notable increase when compared to standard (US) .375 H&H velocities of 2,690 and 2,530 fps, respectively. The result was a comparatively flat trajectory similar to the .30-06 when loaded with a 165-grain bullet of similar profile. Incidentally, since the .375 H&H Magnum cartridge headspaces on the belt, they can be fired in a .375 Weatherby Magnum rifle, which also fire-forms cases. In spite of the large .378 Weatherby Magnum being developed almost 10 years later, Weatherby continues to offer .375 rifles and ammunition.

Reducing ball powder loads may cause erratic pressures and velocities and is generally not recommended. Hodgdon Varget gave outstanding accuracy with 270- and 300-grain bullets, while Hodgdon H-4350 produced almost equal accuracy with more velocity.

Large rifle magnum primers are suggested to achieve proper powder ignition under all temperatures and circumstances. Ammunition to be used in magazine rifles should have a crimp applied to prevent bullets from becoming "deep seated" when subjected to recoil.

Weatherby cases were used exclusively to develop the accompanying handload data and handled maximum loads with ease. Cases made by another manufacturer, or that are fire-formed from .375 H&H Magnum brass, may not handle maximum pressure loads.