.300 Winchester Short Magnum (Using Sierra Bullets)
Date: Apr 29 2015
Notes from the Lab: .300 Winchester Short Magnum (Using Sierra Bullets)
The .300 Winchester Short Magnum (WSM) was introduced in 2001 as a joint effort between Winchester Ammunition, Browning and Winchester/USRAC. The short magnum concept was not a new idea, as wildcatters developed similar cartridges even before World War II, but there was renewed interest in similar wildcat cartridges in the decade previous to the .300 WSM’s introduction.
With trends toward lighter field rifles, the .300 WSM could be housed in a .308 Winchester length action, which reduced weight and overall rifle length. When loaded with 150- to 180-grain bullets, it nearly duplicates .300 Winchester Magnum ballistics and uses slightly less powder. It is suitable for all North American game and African plains game. Most major U.S. rifle manufacturers chamber the .300 WSM; Winchester, Remington, Federal, NoslerCustom and others offer a variety of factory loads for it. In spite of its many virtues, it has not supplanted the .300 Winchester Magnum.
In developing the accompanying data, many of the best loads often resulted in low extreme spreads, often ranging from 5 to 20 fps for a 5-shot string.
Maximum loads should be approached with caution, as the pressure curve can increase rather quickly. Ball powder (or spherical) loads should not be reduced below start charges. It is suggested to keep their load density to at least 85 percent or higher, or erratic pressures and even hangfires can occur. When proper ball powder loads are used, overall accuracy and performance can be excellent. Particularly good performance (accuracy and velocity) was achieved with Winchester 760, Hodgdon H-414, Accurate Magpro and 2700, and Ramshot Big Game. Notable extruded powders included IMR-4350, IMR-4831, Hodgdon 4350, Alliant RL-19, RL-22 and Vihtavuori VV-N560.
Industry maximum overall cartridge length is 2.860 inches, and all loads were within that limit with the exception of the Sierra 190-grain HPBT, 200-grain SBT and 200-grain HPBT bullets. As noted in the charts, these were seated to 2.900 inches and are intended to be fired in single shot mode, as most .300 WSM magazines will not accept cartridges of this length.