The RMCS-4 (Rifle Multi-Caliber System) was Windham's modular platform — a single lower receiver with quick-change uppers in 5.56 NATO, .300 BLK, 7.62x39mm, and .450 Bushmaster. Positioned as a one-lower-many-calibers solution, it competed with the ACR concept at a fraction of the price. Type: Rifle Action: Semi-Automatic Caliber: 5.56x45mm NATO Capacity: 30 Year introduced: 2013, United States Weight: 100.8 oz Overall length: 32.5" Status: Active Intended use: Recreational Shooting, Hunting