300 Winchester Short Magnum (also known as 300 WSM) is a .30 caliber rebated rim bottlenecked centerfire short magnum cartridge that was introduced in 2001 by Winchester.
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 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.
The advantage to this round is ballistic performance 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.
The .300 WSM is adequate for hunting all big game including (but not limited to): moose, black bear, brown bear, elk, mule deer, and white-tailed deer in forests and plains where long range, flat shots are necessary. The .300 WSM is also used in benchrest shooting.
IT has a standard bullet diameter of .308 or 7.62mm and takes advantage of the numerous bullet options available in that caliber.