The 300 Winchester Short Magnum (WSM) was introduced in 2001, the first of what would be several short, fat, unbelted magnums from Winchester, Remington, and Hornady. The theory (and reality) is that burning is more efficient when the propellant column is wider in relation to its length, allowing the primer to ignite a greater percentage of the charge. The burning curve is more efficient, and slightly more energy per grain of propellant is produced. Using a 2.1-inch case, the 300 WSM fits into a short (308 Winchest-length) action, yet produces velocity almost equal to the 300 Winchester Magnum, as examples a 150-grain bullet at 3270 feet per second and a 180-grain bullet at 2970. The 300 WSM was first in its class, and America loves its 30-calibers. As a result the 300 WSM has been the most popular of the new short, fat magnums, with ammunition from multiple sources and rifles chambered by numerous manufacturers.
