The M&P15 Whisper was Smith & Wesson's early entry into the .300 Blackout market, featuring a 16-inch barrel with a threaded muzzle and a 1:8 twist rate optimized for subsonic 220-grain projectiles. Discontinued as the M&P15 line was consolidated. Type: Rifle Action: Semi-Automatic Caliber: .300 Blackout Capacity: 30 Year introduced: 2012, USA Weight: 64 oz Overall length: 32" Status: Discontinued Intended use: Suppressor Host, Home Defense