The MCX Rattler is Sig Sauer's most compact MCX variant, with a 5.5-inch barrel designed for maximum concealability in NFA SBR configuration. Type: Rifle Action: Semi-Automatic Caliber: .300 Blackout Capacity: 30 Year introduced: 2017, Germany Weight: 63 oz Overall length: 25.5" Status: Active Intended use: Special Operations, Law Enforcement