The Sig Sauer MCX-R is built on Sig's MCX platform and uses a short-stroke gas piston system for reliable cycling and reduced recoil. It chambers 5.56 NATO, .300 Blackout, and 7.62x39mm, and features a monolithic upper receiver that allows quick barrel swaps for caliber and length changes. The gas piston system holds up under adverse conditions, making it suitable for tactical work, hunting, and competition.