The 357 SIG round, also designated as 9x22mm, was developed by Swiss-German manufacturer Sig Sauer. Designed after the 10mm auto case, .357 Sig is a 0.355 inch bullet, slightly longer than a .40 S&W round. Note: .40 S&W rounds shouldn’t be used in a .357 Sig barrel, causing possible injury or damage to the firearm. The .357 Sig round is a well regarded, accurate round, used by many law enforcement agencies today.