Winchester's .300 WSM was announced early in 2001. Its fat stubby case has a sharp 35 degree shoulder angle and a .535" diameter rebated rim (to allow operation with standard magnum size bolt faces). The case diameter at the base is .555", its body is 1.664" long to the bottom of the shoulder, and its length is 2.1". The overall cartridge length is 2.86". This new short action .300 magnum is a powerful, compact cartridge. It is suitable for game from the size of deer and antelope to the largest thin-skinned game worldwide.

The .300 WSM has slightly less powder capacity than the standard length .300 Winchester Magnum. It is at its best with bullets of 150-180 grains. With bullets in this weight range its performance is essentially identical to that of the established .300 Win. Mag. because, allegedly, the short case burns powder slightly more efficiently than the longer case. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.