The M4 uses a proprietary action design called the "auto-regulating gas-operated" (ARGO) system, which was created specifically for the weapon.

On May 4, 1998, the United States Army Armament Research, Development and Engineering Center (ARDEC) at Picatinny Arsenal, New Jersey issued Solicitation #DAAE30-98-R-0401 requesting submissions for a new 12 gauge semi-automatic combat shotgun for the U.S.

On August 4, 1998, five samples of the M4 were delivered to Aberdeen Proving Ground, Maryland, and after intense testing, the M4 won the competition.

The short-stroke design uses two self-cleaning stainless steel pistons located just ahead of the chamber to function opposite a rotating bolt, thereby eliminating the need for the complex mechanisms found on other gas-actuated automatics.

The ARGO incorporates only four parts: two symmetrical fore-end shrouds containing two small steel pistons that push directly against the bolt.

[4][note 1] Collapsing the buttstock shortens the weapon by almost 8 in (200 mm), allowing easier storage and transportation; furthermore, it permits better maneuverability around tight corners and over obstacles.

[5] The Picatinny rail built into the top of the shotgun accepts scopes, laser illuminators, night-vision sights and flashlights.

Standard magazine capacity of the civilian version is 5+1, although it is possible to fit 6+1 and two shot extension tubes are sold by Benelli as well as some other companies.