High Quality Content by WIKIPEDIA articles! The .357 SIG pistol cartridge is the product of Swiss-German firearms manufacturer SIG-Sauer, in cooperation with the American ammunition manufacturer Federal Cartridge. While it is based on a .40 S&W case necked down to accept 0.355-inch (9.0 mm) bullets, the .357 SIG brass is slightly longer (0.009-inch (0.23 mm) to 0.020-inch (0.51 mm)). The cartridge is used by a number of law enforcement agencies and has a good reputation for both accuracy and stopping power.