The .358 STA was the second cartridge developed by firearms writer Layne Simpson on the 8mm Remington Magnum case, and it is second in popularity to the 7mm STW, which came first. It has been reported that the first version of the .358 STA was formed by necking up the 8mm Remington Magnum with no other change, but this is not true. It is true for the 7mm STW, because the 8mm Magnum case holds all the powder that can be burned in a bore of that size at an acceptable level of efficiency. But, more powder can be burned in a .35-caliber bore and, right from the start, Simpson chose to reform the case to the Improved configuration with minimum body taper and a 35-degree shoulder angle. The case is formed by necking up the 8mm Remington Magnum case and loadingit with a reduced powder charge with 80 grains of H4350 behind a 250-grain bullet for a popular fire forming load. The first rifle chambered for this cartridge was built by gunsmith Kenny Jarrett, and the first commercial rifles chambered for it were built by A-Square. It was also first to offer loaded ammunition. Layne Simpson introduced the cartridge in the September 1992 issue of Shooting Times, soon after using it to bag an Alaskan brown bear.

​Powerful enough to handle any big-game animal in North America, the .358 STA shoots as flat as a .300 Magnum and delivers more energy to the target than the .375 H&H Magnum. When loaded with a 250-grain bullet, it is about 200 fps faster than the .358 Norma Magnum and duplicates the performance of a cartridge of the 1920s called the .350 Griffin & Howe Magnum.​​

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