The SIG Sauer P320 can be chambered in 9×19mm Parabellum (referred to here as simply 9mm), .357 SIG, .40 S&W, and .45 ACP. The handguns made in 9mm, .357 SIG, and .40 S&W calibers can be easily converted among each to be the other. A change from .357 Sig to .40 S&W requires only a barrel change. The change between 9mm to .357 Sig or .40 S&W and vice versa are accomplished using a caliber exchange kit
The P320 chambered in 9×19mm Parabellum was introduced in the North American market on January 15, 2014 followed by the .45 ACP compact model at the SHOT Show in January 2015. The P320 is a further development of the SIG Sauer P250 utilizing a striker-fired mechanism in lieu of a double action only hammer system. On January 19, 2017, it was announced that a customized version of the SIG Sauer P320 had won the United States Military XM17 Modular Handgun System competition. The full sized model will be known as the M17 and the carry sized model will be known as the M18.