SIG Sauer SIGM400

The SIGM400 is a family of firearms manufactured by SIG Sauer. The M400 is an air-cooled, direct impingement gas-operated, magazine-fed carbine that is based on the earlier AR-15 rifle. Depending on the variant, it can be chambered for 5.56×45mm NATO or .300 AAC Blackout cartridges, and may have a fixed or telescoping stock.
Design details.
Operating mechanism.
The SIGM400 is a semi-automatic firearm in either rifle as the SIGM400 Classic, SRP, Tread, Elite, Predator or pistol as the Elite PSB, intended for law enforcement, military and civilian markets. It fires from a closed bolt and uses a direct impingement gas system.
Features.
The SIGM400 Predator is a rifle while the SIGPM400 Elite PSB is a pistol. The rifles are chambered for either 5.56×45mm NATO with , , , or barrels threaded 1/2x28, or chambered for .300 AAC Blackout with or barrels which are threaded 5/8x24 for muzzle devices such as sound suppressors. There are California compliant ("featureless") models for both. The .300 AAC Blackout model is tailored specifically for efficient use with suppressors. The Picatinny rail supports optical, electro optical, or iron sights. SIG Sauer also manufactures suitable suppressors.
The SIGPM400 Elite PSB pistol is chambered for 5.56×45mm NATO with an barrel and is chambered for .300 AAC Blackout with a barrel. Both use a Pistol Stabilizing Brace accessory.
Ergonomically, the SIGM400 is an AR-15 style rifle. It has a safety lever on the left side, to be used by the thumb of the shooting hand. Some newer models have an ambidextrous safety selector. The front gas block is railed to accept the front sight with a flip-up sight post. All models accept AR-15-style box magazines. The rifle is hammer-fired with a single-stage trigger in most models. Some models include a two-stage trigger from the factory.
The SIGM400 has a telescoping skeletonized buttstock. The ACE-style stock moves forward and rearward in six positions. A spring-loaded release underneath the buffer tube area locks the stock into each position.