.270 Winchester Short Magnum
Date: Mar 06 2014
The .300 Winchester Short Magnum was introduced to the shooting public in 2001. It featured a short, fat, beltless case with a comparatively sharp 35-degree shoulder. Overall cartridge length was 2.860 inches, which allowed it to be housed in .308 Winchester length bolt-action rifles, reducing rifle weight and overall length.
The .270 WSM was introduced in 2002, based on the above case, but with slight alterations to the shoulder position. Powder capacity is increased when compared to the .270 Winchester, which typically results in velocity increases of around 170 to 250 fps, depending on load. The .270 WSM offers a flat trajectory and is an excellent choice for deer sized game in open country. With correct bullets it is suitable for elk and African plains game.
There were no difficulties in developing high performance handloads; however, a rather large swing in case neck thickness was noticed. Most currently available cases measure between .014 to .018 inch, but there were some Winchester manufactured cases that were as much as .022 inch thick. If these cases are used in a chamber that is on the minimum side of industry specifications, pressures will rise prematurely. These out-of-specification cases have caused grief among die manufacturers, and due to increased pressures should generally be avoided when assembling handloads. As a reminder, never begin with maximum loads; begin with "start" loads and carefully watch for signs of excess pressure as powder charges are increased.
Large rifle magnum primers are generally suggested to obtain reliable ignition with all powders and in a wide range of temperatures.
Several powders proved accurate and yielded low extreme spreads. Examples include Alliant RL-15, RL-19; Hodgdon H-4350, H-4831; Vihtavuori N-160, N-165 and IMR-4350.