.300 Winchester Magnum - Design and Specifications

Design and Specifications

The .300 Winchester uses the same case head design of the .375 H&H Magnum, its parent cartridge. The taper of the cartridge was reduced to provide the cartridge with more volume so as to increase its potential powder capacity. The lengthening of the case and the move of the shoulder forward over the .338 Winchester Magnum allowed for the reaming of the .308 Norma Magnum or .30-338 Winchester chamber to dimensions of the .300 Winchester Magnum. The down side was a neck which was shorter than the caliber of the bullet it fired, which meant that the bullet had to be seated more deeply in the case.

Both SAAMI and CIP have provided specifications for the .300 Winchester Magnum cartridge. No divergence between CIP and SAAMI dimensional values exist for this cartridge. SAAMI recommends a bore diameter of 0.300 inches (7.6 mm) and a groove diameter of 0.308 inches (7.8 mm). SAAMI recommended a six-groove barrel with each groove being 0.110 inches (2.8 mm) wide. Recommended twist ratio is 1:10.

While case volume will vary from manufacturer to manufacturer, the typical Winchester case capacity is of 93.8 grains of H₂O (6.08 cm3). The maximum pressure of the cartridge given by CIP is 4,300 bar (62,000 psi) and SAAMI recommended maximum pressure is 64,000 psi (4,400 bar).