The M4 H2O applies a full Titanium Cerakote finish to all metal components of the standard M4 for maritime and coastal use. The H2O designation indicates the corrosion-resistant treatment — functionally the most corrosion-resistant semi-automatic shotgun from any major manufacturer. Type: Shotgun Action: Semi-Automatic Caliber: 12 Gauge Capacity: 7 Year introduced: 2008, Italy Weight: 112 oz Overall length: 40" Status: Active Intended use: Maritime, Law Enforcement, Coastal