The Windham Weaponry RMCS-4 (Rifle Multi-Caliber System) is designed for easy caliber conversion between 5.56, .300 BLK, and .450 BM with upper receiver swaps. The 16-inch 5.56 configuration is the base model. The RMCS-4 lower is specifically designed to accept multiple upper caliber families, making it a versatile platform for shooters who want caliber flexibility without purchasing multiple complete rifles. Type: Rifle Action: Semi-Automatic Caliber: 5.56x45mm NATO Capacity: 30 Year introduced: 2013, USA Weight: 64 oz Overall length: 32.5" Status: Active Intended use: Home Defense, Hunting, Target Shooting