Sig Compact S

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Sig Compact S

The SIG Sauer P320 is a modular semi-automatic pistol made by SIG Sauer, Inc. of Exeter, New Hampshire, and SIG Sauer GmbH of Eckernförde, Germany. It is a further development of the SIG Sauer P250, utilizing a striker-fired mechanism in lieu of a double action only hammer system. The P320 can be chambered in 9×19mm Parabellum.357 SIG, .40 S&W, and .45 ACP, and can be easily converted from one caliber to another—a change from .357 SIG to .40 S&W requires only a barrel change; a 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 15 January 2014, followed by the .45 ACP compact model at the SHOT Show in January 2015. On 19 January 2017, it was announced that a customized version of the SIG Sauer P320 had won the United States Army‘s 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.


From the beginning, the P320 was built to be a pistol that could adapt to meet the user’s specific needs. From grip modules and magazines to custom slides, barrels, and optics, the P320 can be configured in thousands of different ways to make your P320 unique and exactly the pistol you are looking for.

The P320 CustomWorks Studio FCU program takes that idea and brings it to an unprecedented new level. Take a look at the video to get a more in-depth overview of what this program has to offer. You can also click one of the buttons above to either start building your custom P320 or to purchase your CustomWorks P320 FCU.

  • Exclusive Titanium Nitride Frame
  • Titanium Nitride Skeletonized Trigger
  • Custom “FCU ******” Serial Number
  • Compatible with all 9mm/357SIG/40SW P320 Post-Upgrade accessories
  • Build a custom P320 with a full line of performance parts and accessories

Design details


The P320 was designed to be ambidextrous in handling, sporting a catch lever on both sides of the slide and user-reversible magazine release, and all other operating controls are designed so they can be operated from either side. The firearm can be field stripped with no tools. Additionally, the firearm can also be field stripped without depressing the trigger, an additional safety feature to prevent negligent discharge of the weapon.

SIG Sauer P320 Full Siz

SIG Sauer P320 RX (with Romeo 1 optical reflex sight)

The X Series lineup includes the following grip module sizes:

SIG Sauer P320 fire control unit

Trigger system

The P320 trigger is available in standard (solid) and tabbed (with trigger safety).

M17 and M18

When the requirements were formulated for a new handgun for the US Army one of the tenets of the proposal was that an existing model handgun was desired to fulfill the requirements laid out in the Modular Handgun System Request for Proposal, known as the XM17 Procurement. SIG Sauer submitted a P320 with a number of modifications and submitted them for the XM17 Modular Handgun System competition.

Modifications include:

  • Slide cut-out to facilitate the addition of a reflex sight. (This is the slide from the RX Series)
  • Ambidextrous thumb safety
  • Loaded chamber indicator
  • Improved slide sub-assembly to capture small components when disassembled
  • Improved trigger “mud flap” to prevent foreign debris from entering the pistol action
  • 4.7-inch (120 mm) barrel length in full size pistol
  • 3.9-inch (99 mm) barrel length in compact pistol
  • chambered in 9×19mm Parabellum (can be adapted to fire larger calibers like .357 SIG and .40 S&W)
  • Pistols chambered in 9mm can feature a 17-round magazine as standard with optional 21-round extended magazines available.

On 19 January 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 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.

In May 2017, the Army announced that the first unit that will receive the M17 would be the 101st Airborne Divisionby 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.

On 17 November 2017, soldiers of the 101st Airborne received the first XM17 and XM18 pistols, with over 2,000 handguns delivered. The XM17 has better accuracy and ergonomics and tighter dispersion than the M9. It will also be fielded more widely, being issued down to squad and fireteam leaders; while special forces would dual-arm all of its members with a pistol and rifle, previously junior leaders in regular infantry units were excluded from carrying sidearms but policy was changed to give them more choices and options in close quarters battle situations. All Army units are planned to have the M9 replaced with the M17 within a decade.


Initial production models of the P320 were noted to have a ‘drop safety’ issue if the firearm was dropped on a specific angle causing it to discharge. Sig has since refitted the P320 with a new trigger with reduced mass and a new striker disconnect that makes it drop safe. Sig also offers a voluntary exchange program to fix any defective P320s.

Apart from initial teething issues, the P320 has proven itself to be an extremely reliable pistol for civilian, law enforcement and military use. Many police departments in the US and around the world have started issuing their officers P320s.

Drop firing problem

In late July 2017, the Dallas Police Department in Texas instructed all personnel to stop carrying the P320 pending an investigation. There were concerns that the firearm may discharge when it is dropped and the back of the slide hits the ground at a 33-degree angle. The problem was thought to be related to the trigger weight; some triggers were heavy enough that they essentially continued to move due to inertia after the gun hit the ground. Internet publications, such as, conducted independent tests that appeared to confirm potential drop firings (at a 40% rate).

On 8 August 2017, SIG Sauer issued a notice that they would upgrade all P320s to address the issue. The upgrade is described on the company’s website as: “This will include an alternate design that reduces the physical weight of the trigger, sear, and striker while additionally adding a mechanical disconnector.” The P320 upgrade program is detailed on the SIG Sauer website at: P320 Voluntary Upgrade Program.


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