The overall cartridge length is 72.6 mm. The cartridge case length is 53.34 mm. The bullet diameter is .308 in (7.82 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. The .30-06 Springfield holds 69 grains; .308 Winchester holds 56 grains; 30-30 Winchester holds 45 grains. The .300 Winchester Magnum has a case capacity of 93.8 grains. 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.
The advantage to this round is the ballistic performance is nearly identical to the .300 Winchester Magnum in a lighter rifle with a shorter action burning 8 - 10% less gunpowder. A disadvantage of cartridge case designs with relatively large case head diameters lies in relatively high bolt thrust levels exerted on the locking mechanism of the employed firearm. Also, in small ring actions the larger chamber diameter removes more steel from the barrel tenon, making it weaker radially.