M4 Tactical - Ghost Ring This is the foundation on which all Benelli M4 Auto-Regulating Gas-Operated (A.R.G.O) semi-automatic shotguns are built. The A.R.G.O. system makes them fast cycling and ultrareliable. Optimized for tactical response and personal defense, the M4 features a tactical stock, adjustable rear ghost-ring site, windage-adjustable front sight, and a Picatinny rail for a light or optics. Specifications Caliber or Gauge 12 Barrel length (Inches) 18.5" Chamber (Inches) 3" Choke M Product Type Semi-Auto KEY FEATURES Auto-Regulating Gas-Operated: This piston-driven Auto-Regulating Gas-Operated (A.R.G.O.) system was designed for and approved by the U.S. Marine Corps.