The SIG MCX Rattler was first introduced in mid-2017 as a dedicated subcompact version of the SIG MCX family of rifles. It is believed that US-based Sig-SAUER development team produced this specific version upon solicitation from US-SOCOM for a compact PDW (Personal Defense Weapon) conversion kit for the existing M4A1 carbines in use by US military.
This request calls for select-fire upper receivers with 5.5-inch barrels, chambered for 5.56×45 NATO and .300 AAC Blackout ammunition. While results of this solicitation remain unclear as of moment of this writing (Feb, 2018), SIG-Sauer has released two civilian, semi-automatic only versions of the SIG MCX Rattler, the “Short-Barreled Rifle” (SBR), which is an NFA’34 item and requires prior BATF approval for purchase, and as a “handgun with pistol-stabilizing brace”, which does not require any special licensing or subsequent registration, as per US laws. Initial versions of the semi-automatic SIG MCX Rattler are available only in .300BLK, but it possible that 5.56mm /.223 versions could be added later. Also, while MCX Rattler can be used as an upper to convert any existing M4 carbine or AR15 rifle lower receiver to this short configuration, SIG now offers those guns as a complete packages, with dedicated MCX lower receivers.
SIG MCX Rattler is a gas operated, select-fire (military) or semi-automatic only (civilian) weapon. It uses short stroke gas piston operating system with dual position gas regulator, for normal or suppressed use. Bolt group is proprietary, with AR15-style bolt and special bolt carrier. Dual return springs are hosted around guide rods inside the upper receiver, above the bolt, which allows for use of a conventional side-folding stock. Upper and lower receivers are made from aluminum alloy and connected by two cross-pins. Controls are ambidextrous. In military and civilian SBR versions SIG MCX Rattler is equipped with side-folding stock, made from aluminum alloy. It folds to the left and does not interfere with normal operation of the gun when folded. Civilian “pistol” version is equipped with telescoping “pistol-stabilizing brace”. Ammunition is fed from any M16 / AR15 compatible magazines. Barrel is enclosed into aluminum alloy forend with M-LOK interface, and has a flash hider with quick-detach interface for sound suppressor (silencer). Sighting equipment is installed using integrated Picatinny rail on the top of the upper receiver.
|Full text name||SIG MCX Rattler assault rifle, semi-automatic carbine and pistol (USA)|
|Caliber cartridge||.300 Whisper / .300 AAC Blackout (7.62x35)|
|Overall length, mm||597|
|Length, folded, mm||406|
|Barrel length, mm||140|
|Weight empty, kg||2.59|
|Magazine capacity, rounds||30|
|Cyclic rate of fire, rounds/min||700-900|