7mm STW / Shooting Times Westerner
Date: Apr 01 2015
Notes from the Lab: 7mm STW/Shooting Times Westerner
The 7mm Shooting Times Westerner (STW) was developed as a wildcat cartridge by Layne Simpson around 1989. It was based on the 8mm Remington Magnum case necked to 7mm (although the final version has slight changes). The overall cartridge length is 3.600 inches, the same as the .375 H&H Magnum, so it requires a long action to house it. Simpson was a staff writer for Shooting Times magazine, so the cartridge was promoted and became popular enough that by 1997 Remington began producing ammunition (now discontinued) and SAAMI officially adopted it at about the same time. Federal, A-Square and Nosler Custom also began offering factory loads.
The 7mm STW offers a notable powder capacity increase when compared to the Weatherby or Remington 7mm magnums, and will usually add 125 to 200 fps velocity with the same weight bullets. This performance is not free, as it thrives on long barrels of 26 inches or more, and throat erosion is increased. Nonetheless, it is a good open country big game cartridge.
As expected better overall accuracy was observed with Hornady bullets weighing 154 to 175 grains when compared with the 120- and 139-grain bullets. Generally speaking, as powder charges approached maximum, extreme velocity spreads were reduced and accuracy increased.
None of the powders tried filled the case to 100 percent capacity. The best performing powders included Hodgdon H-1000 and H-4831, Alliant RL-22 and RL-25, IMR-7828 and Vihtavuori VV-24N-41. A large rifle magnum primer is suggested, with the Federal 215 used herein.