<Li> chambered in 9 × 19mm Parabellum (can be adapted to fire larger calibers like . 357 SIG and . 40 S&W) </Li> <Li> Pistols chambered in 9mm can feature a 17 - round magazine in standard with optional 21 - round extended magazines available . </Li> <P> On January 19, 2017, it was announced that the SIG Sauer P320 MHS variant had won the United States Military's Modular Handgun System trials . The P320 will be known as the M17 (full size) and M18 (compact) in U.S. Military service . Though the pistol will remain chambered in 9 x 19mm Parabellum rather than a larger caliber, the contract allows the Army and other services to procure Sig Sauer's proposed XM1152 Full Metal Jacket and XM1153 Special Purpose ammunition . The ammunition chosen to go with the pistol is a "Winchester jacketed hollow point" round . </P> <P> In May 2017, the Army announced that the first unit that will receive the M17 would be the 101st Airborne Division by the end of the year . At the same time, the rest of the U.S. Armed Forces revealed they also intend to acquire the handgun, making it the standard sidearm for the entire U.S. military . The services plan to procure up to 421,000 weapons in total; 195,000 for the Army, 130,000 for the Air Force, 61,000 for the Navy (XM18 compact version only), and 35,000 for the Marines . </P>

What is the difference between the m17 and m18