The SIG Sauer M400 is a family of AR-15-style rifles and pistols that cater to a variety of shooting applications, including self-defense, recreational shooting, and professional use. The M400 is built on a direct impingement gas system, which is similar to the original AR-15 design. This system allows for smoother operation and ease of maintenance. The M400 is chambered in 5.56×45mm NATO, .223 Remington, and .300 AAC Blackout, making it versatile for different calibers and shooting preferences. Depending on the variant, barrel lengths range from 9 to 20", allowing for a variety of applications from compact models ideal for maneuverability to longer-barrel rifles focused on precision. The SIGM400 line offers several configurations, including the SIGM400 Predator for hunting, with a 16" barrel, and the SIGPM400 Elite PSB, which is a pistol variant featuring an 11.5" barrel in 5.56 NATO or a 9" barrel in .300 Blackout. The Pistol Stabilizing Brace (PSB) is a key accessory in the pistol models, offering better control and stabilization. The M400 features a free-floating aluminum handguard, offering ample rail space for optics, lights, and other accessories. Variants like the SIGM400 TREAD emphasize modularity, allowing shooters to add components like suppressors or optics to suit their preferences. The M400 rifles and pistols are praised for their reliability, accuracy, and customization options.