SIG Sauer P320

Design

The P320 evolved from the SIG Sauer P250, replacing its double action only hammer system with a striker-fired mechanism. The trigger pull, listed at 29 N, results from a combination of a tensioned striker spring, trigger shoe and trigger bar dimensions, sear/striker engagement, and a balanced trigger system. The pistol can be chambered in 9×19mm Parabellum, .357 SIG, .40 S&W, .45 ACP, and 10mm Auto, with caliber conversions possible; a change from .357 SIG to .40 S&W requires only a barrel change, while switching between 9mm and .357 SIG or .40 S&W uses a caliber exchange kit. However, .45 ACP and 10mm require larger components and are not interchangeable with smaller calibers.

The P320 is ambidextrous, featuring a catch lever on both sides of the slide and a user-reversible magazine release. It can be field-stripped without tools and without depressing the trigger, an added safety measure. The fire control unit is removable, allowing grip size changes. The trigger shoe is available in solid all-metal, curved, or straight variants from SIG and third-party suppliers.

Variants

The full-sized model is designated the M17, and the compact carry-sized model the M18. The X Series lineup includes grip modules in full size, which fits any SIG P320 full-size slide in 9mm, .40 S&W, and .357 SIG, and compact size. In January 2019, SIG Sauer announced the XCompact handgun, available as of March 2020 in 9mm only; its grip module is the smallest SIG currently carries, with no subcompact X Series grip module released. In May 2022, SIG Sauer announced the P320 XTEN, a 10mm Auto variant.

The U.S. Army's Modular Handgun System requirements led to the XM17 Procurement, for which SIG Sauer submitted a modified P320. Features included a 3.9 in barrel in carry size, 4.7 in barrel in full size, ambidextrous thumb safety, chambering in 9×19mm Parabellum (adaptable to .357 SIG, .40 S&W, and .45 ACP), an improved slide sub-assembly, an improved trigger mud flap, a loaded chamber indicator, standard 17-round magazines with optional 21-round extended magazines, and a slide cut-out for a reflex sight. On January 19, 2017, the P320 MHS variant won the U.S. Military's Modular Handgun System trials, becoming the M17 and M18 in service, remaining in 9×19mm Parabellum.

Problems

Initial production P320s exhibited a drop safety vulnerability when dropped at a specific angle and height outside SAAMI and NATO standards, potentially causing discharge. SIG Sauer later refitted the pistol and offered a voluntary upgrade program for early models. In late July 2017, the Dallas Police Department instructed personnel to stop carrying the P320 pending investigation, citing concerns about discharge when dropped at a 33-degree angle, thought to relate to trigger weight inertia. On August 8, 2017, SIG Sauer announced an upgrade involving an alternate design that reduces the physical weight of the trigger, sear, and striker and adds a mechanical disconnector.

Issues of drop firing or holster discharge continued sporadically, with at least six departments removing the P320 from service. Around 400 P320s procured for Canadian Joint Task Force 2 in 2019 were withdrawn after a misfire injured a soldier during a training exercise in November 2020; the earlier P226 pistols were reinstated. A June 2021 technical investigation attributed the misfire to partial trigger depression by a foreign object combined with slide movement while holstered, with a contributory factor being use of a holster designed for a different pistol. The pistols remained in storage pending a third-party safety assessment, which concluded by June 2022, leading to a decision to reinstate the P320.

Lawsuits

The P320 has been involved in several lawsuits. In May 2017, Steyr Arms sued SIG Sauer in federal court in Alabama, claiming the P250 and P320 infringed on a Steyr patent for a handgun with a removable chassis. Steyr asked for an injunction to stop sales. In February 2020, a New Hampshire court ruled in SIG Sauer's favor, finding no patent infringement and dismissing the case.

In August 2017, a Stamford police officer sued SIG Sauer in Connecticut after his holstered P320 allegedly fell from his vehicle and fired into his knee. SIG Sauer settled that case in June 2018. In May 2018, a Virginia deputy sheriff sued after her holstered P320 allegedly discharged while she was removing it, breaking her femur. That case settled in May 2019, on the second day of trial.

In March 2019, Glock challenged the Danish military's adoption of the P320 X-Carry, arguing it did not meet a specification that no part could be assembled incorrectly. Glock and its Danish distributor won, proving the ejector could be misassembled. They were awarded 30,000 Danish kroner, and the purchase was canceled. The contract was later reissued with different requirements, which the P320 then met.

Did You Know?

• In April 2017, Caracal International was made a licensed producer for the P320.
• In December 2025, the SIG Sauer P320 replaced the SIG P220 as the Swiss Army's new service pistol.