The M4 Tactical shotgun is the combat service shotgun of the U.S. Joint Services today.
The M4 is a unique, Auto-Regulated Gas-Operated (A.R.G.O.) semi-auto 12-gauge.
The metalwork is anodized or coated with heavy phosphate to prevent corrosion under the most grueling conditions.

Ghost-ring sights for quick target acquisition
Picatinny rail for mounting scopes, sights, and optics
Extended magazine will hold seven 2-3/4" or 3" magnum shells

The M4 looks rather similar to the M3 Super 90, but differs in having a gas system instead of the inertia driven system. The double gas piston setup makes the M4 cycle more reliable in arduous circumstances and with multiple attachments, but dispenses of the pump-action ability. A Picatinny rail allows optics to be fitted. The M4 is also fitted with a retracable stock and pistol grip as standard, although a fixed stock is available.