February 22, 2012: 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.
The first versions of this weapon weighed nine pounds and carried only three rounds. The design evolved, over the last decade, into the current M26. Troops have been testing it in combat for five years. There were complaints about the cocking mechanism, which uses a bolt instead of a pump action (which many troops expressed a preference for). The final design improved the cocking mechanism and the reliability of the magazines.
Currently, troops use a conventional (Mossberg) 12 gauge shotgun for getting locked doors open in a hurry. The M26 proved very reliable during testing, with over 20,000 rounds being fired. Large quantities of the M26 will be reaching the troops soon, although only 2,500 are currently on order.
All this took so long because the army wanted to perfect similar existing designs from the 1980s and 1990s. Many troops bought these earlier weapons with their own money or special funds each brigade or division has for "special" equipment.