.300 Winchester Short Magnum (also known as .300 WSM) is a .30 caliber rebated rim bottlenecked center fire short magnum cartridge that was introduced in 2001 by Winchester. The .300 WSM cartridge overall length is 72.64 mm, cartridge case is 53.34 mm in length and the bullet diameter is .308 in (7.62 mm), which is common to all U.S.A .30 caliber cartridges. The principle at work in the .300 WSM short magnum cartridge is the advantage of fitting larger volumes of powder in closer proximity to the primer’s flash hole, resulting in more uniform, consistent ignition. In field use, the .300 WSM round mirrors the performance of its older counterpart, the .300 Winchester Magnum, which is based on a modified.375 Holland & Holland belted magnum casing.
The advantage to the .300 WSM round is ballistics that are nearly identical to the .300 Winchester Magnum, but in a lighter rifle with a shorter action. 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 in a radial direction .