[2] The M26-MASS is a lightweight underbarrel shotgun configured to be secured to a main rifle, developed by C-More Systems and manufactured by Vertu Corporation[3] and originally marketed toward special operations forces.

It attracted the interest of soldiers being deployed to Afghanistan who wanted a lightweight system that could eliminate the need to carry additional weapons.

The idea was to provide soldiers with lightweight accessory weapons which could be mounted underbarrel of the standard issue M16 rifle or M4 carbine.

The M26-MASS improved upon the original Masterkey concept with a detachable magazine option and more comfortable handling, thanks to a bolt-operated system which is manually cycled for reloading and is characterized by a bolt which must be moved backward to remove a spent case and forward to chamber a new cartridge.

The relatively large bolt handle is located closer to the rear rather than the slide on the Masterkey pump shotgun, and thus is easier to cycle in combat.