The Benelli M4 Super 90 is an Italian semi-automatic shotgun manufactured by Benelli Armi SpA.
The M4 was the first gas-operated shotgun produced by Benelli. Its function is designed around an entirely new method called the “auto regulating gas operated” (ARGO) system. The short-stroke design uses two stainless-steel self-cleaning pistons located just ahead of the chamber to function opposite the rotating bolt, thereby eliminating the need for the complex mechanisms found on other gas-actuated automatics. The ARGO incorporates only four parts: two symmetrical shrouds containing two small steel gas pistons.
Additionally, the weapon is self-regulating for use with cartridges of varying length and power levels. It can fire 2.75 (70 mm) and 3-inch (76 mm) shells of differing power-levels without any operator adjustments and in any combination. Low-power rounds, such as less-lethal rubber pellets, must be cycled manually.
The sights are military-style ghost ring and are adjustable in the field using only a cartridge rim. The MIL-STD-1913 Picatinny sight rail on top allows use of both conventional and night-vision sights, while retaining use of the original sights.