The overall cartridge length is 72.6 mm. The cartridge case length is 53.34 mm. The bullet diameter is .308 in (7.62 mm), which is common to all U.S. .30 caliber cartridges. The principle at work in the short magnum cartridge is the fitting of larger volumes of powder in closer proximity to the primer's flash hole, resulting in more-uniform ignition. .300 WSM has a case capacity of 80 grains of H2O. The .30-06 Springfield holds 69 grains of H2O; .308 Winchester holds 56 grains of H2O; 30-30 Winchester holds 45 grains of H2O. The .300 Winchester Magnum has a case capacity of 93.8 grains of H2O. While providing ballistic performance nearly identical to that of the .300 Winchester Magnum, .300 WSM does this with about 14 grains less powder. The .300 WSM also head-spaces off of the case shoulder, versus the older .300 Winchester Magnum's belted head space design.