.300 Remington Short Action Ultra Mag
Date: Apr 15 2020
Remington developed the .300 Short Action Ultra Mag (aka .300 Remington SAUM) during the 1990s, along with the .300 Remington Ultra Mag. Each was based on a beltless case inspired by the .404 Jeffery, but was distinctly different. The .300 RUM was introduced first (1999), while introduction of the RSAUM was delayed a couple of years to allow the furor of the .300 RUM to settle down. Winchester beat Remington to the punch and in 2001 began offering the .300 Winchester Short Magnum (.300 WSM), with the .300 RSAUM being introduced soon thereafter. In spite of these two short magnum cartridges being almost ballistically identical, and each functioning in .308 Winchester action lengths, the Winchester version had a head start and offered a slight velocity edge, and remains most popular. Nonetheless, the .300 RSAUM is an outstanding cartridge. It features a 30-degree shoulder (as opposed to the 35-degree shoulder of the .300 WSM), and there are other slight dimensional differences preventing interchangeability.
In developing the accompanying data, extreme spreads were often unusually low and accuracy outstanding. Many of the better powders and loads produced extreme spreads between 5 to 10 fps for a five-shot string.
In spite of the test rifle featuring a comparatively short 22-inch barrel, it still produced over 3,000 fps with 150- and 165-grain bullets, while 180- and 190-grain bullets reached around 2,900 fps with select powders. The Hornady 220-grain Round Nose bullet tends to seat deeply into the case and reduces precious powder capacity, and is a less popular choice in all short magnums. Nonetheless, it can be pushed to around 2,600 fps and easily outperforms the proven .30-06 Springfield loaded with the same bullet.
Several powders produced excellent accuracy and velocity including IMR-4895, 4064 and 4350; Vihtavuori N-140, Hodgdon Varget, H-4895, H-4350; Winchester 748 and 760; Alliant Reloader 15 and Accurate 4064. Many of the accompanying handloads feature a compressed powder charge; however, none required the use of a drop tube to allow bullets to seat to their correct overall length.
Industry Maximum Average Pressure is established at 65,000 psi, with none of the accompanying loads exceeding that figure.