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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

.300 Weatherby Magnum

Author: Brian Pearce
Date: Apr 15 2020

During World War II Roy Weatherby began working on a series of high velocity cartridges that would ultimately range from .22 through .45 caliber. The .300 Weatherby Magnum was one of the first, based on the .300 H&H Magnum case blown out to increase powder capacity and velocity and featured a unique double radius shoulder. Weatherby first offered proprietary .300 Weatherby Magnum ammunition in 1948, and it has been the most popular cartridge in the product line. It was originally offered in custom built (usually Mauser 98 based) rifles, but by the late 1950s it was offered in the Weatherby Mark V and eventually the Vanguard rifle series. Several other manufacturers were quick to recognize the demand and began offering rifles so chambered, including the German based Colt Sauer, Sako, FN and many others. Beginning in 1994 many Weatherby proprietary cartridges were introduced to SAAMI and became industry standardized cartridges. As a result, major U.S. companies such as Remington, Ruger and Winchester began offering rifles and several domestic (and foreign) companies now offer ammunition.

Traditional advertised velocities typically push a 150-grain bullet at 3,540 fps or a 180 grain at 3,240 fps, both from a 26-inch barrel. Weatherby currently lists 12 loads with a variety of bullets from 150 to 200 grains; velocities vary depending on bullet style. For reference, the Weatherby 180-grain SP factory load was shot in our test rifle with a 24-inch barrel and averaged 3,133 fps.

Weatherby cases, manufactured by Norma of Sweden were used to develop all of the accompanying data. They are of particularly high quality and handle loads that are approaching maximum pressure with ease. In my experience, some cases from other manufacturers manifest pressures much earlier than the Weatherby/Norma cases, which can result in premature sticky extraction.

When loaded with 150- through 220-grain bullets, the .300 Weatherby Magnum thrives on slow burning magnum rifle powders. Notable performers included Hodgdon H-4831 and H-1000; Alliant RL-22 and RL-25; IMR-7828 and IMR-4831. Large rifle magnum primers are strongly suggested to achieve reliable ignition. The current industry pressure guideline is 65,000 psi, with all loads being within that limit.