The SIG MCX is a series of self-loading rifles[disambiguation needed] designed and manufactured by SIG Sauer, featuring a short-stroke gas piston system, carried over from the SIG MPX submachine gun. The rifle is produced in both selective fire and semi-automatic configurations. It is available in rifle, short-barreled rifle, and pistol (generally considered as a compact carbine) configurations.
The SIG MCX was first introduced at SHOT Show 2015.
In 2016, SIG recalled some of the rifles that had the first generation bolt carrier group.
The SIG MCX series features a short-stroke gas piston system to reduce recoil and improve the reliability of the weapon; this was based on the design of the earlier SIG MPX. The MCX features a system that allows for conversion between 5.56×45mm NATO, .300 AAC Blackout, and 7.62×39mm ammunition, using standard 5.56 mm STANAG magazines for 5.56×45mm NATO and .300 AAC Blackout, and specially designed STANAG-compatible magazines for 7.62×39mm.The MCX is designed to deliver optimal performance with .300 AAC Blackout and an optional suppressor.
The barrel's profile is tapered at the crown to allow the installation of muzzle devices and direct-thread sound suppressors without the use of washers that degrade performance and allows the devices to self-center on installation. The barrel can be changed in a matter of seconds to another length or a different caliber. Additionally the barrels are nitride coated for corrosion resistance. It features hardened steel wear points.
All MCX variants have a forend made of aluminum with a KeyMod system to add accessories. Controls are mostly ambidextrous including the charging handle but not the bolt release. Four types of stocks are available for the MCX carbine.
SIG designed the upper receiver to be compatible with standard AR-15 and M16 lower receivers with the help of an adapter. The overall layout of the two rifles is similar.
