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The Ultimate Reloading Manual
Wolfe Publishing Group
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The Ultimate Reloading Manual
hodgdon load data

.30-378 Weatherby Magnum (using Sierra bullets)

Author: Brian Pearce / Wolfe Publishing Co.
Date: Apr 01 2016

The .30-378 Weatherby Magnum was around for decades as a wildcat cartridge, the large .378 Weatherby Magnum case necked to .30 caliber.  In 1998 Weatherby introduced it as a standard cartridge and began offering rifles and ammunition.  It features the traditional Weatherby double-radius shoulder and has an overall length of 3.648 inches, which requires a large action (such as the Mark V) to house it.  Factory loads are advertised to push Nosler 165-grain Ballistic Tips at 3,500 fps and 180-grain bullets at 3,420 fps, or the Nosler Partition 200-grain at 3,160 fps.  It has enjoyed some popularity in long-range competition as many load and bullet combinations remain supersonic at 1,000 yards, but the cartridge also gained acceptance for hunting big game in open country.  Weatherby indicates that the cartridge remains one of its top sellers.

Case capacity can be as high as 120-grains with some propellants, and there are only a few slow-burning powders suitable to take advantage of its over-bore design.  This performance is not free; recoil and muzzle report are significant (at least in field weight rifles), and throat erosion rate results in rather short barrel life.

To prevent erratic ignition and hang-fires, do not reduce powder charges below “start” loads, and use only large rifle magnum primers with the Federal 215 used to develop the accompanying data.

Ammunition that is to be used in bolt-action repeating rifles should have the bullets crimped in place to prevent their being deep-seated when subjected to pounding recoil while in the box magazine.