The MCX Virtus is SIG Sauer's modular rifle platform, designed around a short-stroke piston operating system with an adjustable gas block. The Virtus accepts barrels in multiple lengths (9", 11.5", 16") and can be converted among 5.56 NATO, .300 Blackout, and 7.62x39 by swapping the barrel and bolt. The folding stock is a genuine improvement over the AR-15's fixed buffer tube — the MCX can fold to a fraction of an AR's length. Evolved from the Special Operations-developed MCX platform originally designed for the US Army. Type: Rifle Action: Semi-Automatic Caliber: 5.56x45mm NATO Capacity: 30 Year introduced: 2016, USA Weight: 6.5 oz Overall length: 35" Status: Active Military use: Yes Intended use: duty, military, law_enforcement, hunting