The lightweight M26 12-Gauge Modular Accessory Shotgun System (MASS) attaches to the M4 Carbine and zeroes to the host weapon. It is also designed to operate as a stand-alone system, and comes with a recoil-absorbing, collapsible buttstock. With a Picatinny rail on top, the receiver can be used to mount sighting equipment. The bolt handle (charging handle) is mountable on either side for ambidextrous handling.
After over a decade of development, and testing and tweaking, the U.S. Army is finally issuing the M26 12 Gauge Modular Accessory Shotgun Systems (MASS) to the troops. There are two versions of MASS. The one that attaches underneath the barrel of an assault rifle weighs 1.2 kg (2.7 pounds) and is 420mm (16.5 inches) long. The standalone version weighs 1.9 kg (4.25 pounds) and is 610mm (24 inches) long (with the stock collapsed). Both versions of the M26 have a five round magazine and are basically a 12 gauge shotgun that can be operated right or left handed. It fires solid shot for blasting open closed doors or lower velocity, non-lethal (most of the time) rubber slugs for dealing with hostile crowds.