The M26-MASS (Modular Accessory Shotgun System) is a shotgun configured as an underbarrel ancillary weapon attachment mounted onto the handguard of a service rifle, usually the M16/M4 family of United States military, essentially making the host weapon a combination gun. It can also be operated as a stand-alone shotgun by attachment to a pistol grip/collapsible buttstock module. Rollout commenced in 2013, replacing the M500 shotguns in service.
