The MASS is designed to aid in faster transitions from the shotgun to the rifle during breaching operations, but has other applications including less-than-lethal rounds. It mounts beneath the barrel of an M4 and can be attached to a stock and used as a standalone shotgun. It is a 12-gauge system and has a five round magazine.
I can't wait to hear how it's received by Joe. Sure, it's great to always have a shotgun at the ready. But, I wonder how long it will take for guys to start bitching about always lugging a shotgun on the front of their weapon. There's a big difference between 4lbs on the front of an M4 vs. 7lbs of a Remington 870 on their back. Like the adoption of any new piece of gear, it's going to be a training issue as much for leaders as grunts. Commanders are going to have to learn to deploy these weapons appropriately or risk guys "forgetting" them when they step. I suspect the compact M26 will see more duty as a standalone weapon than it will attached to carbines.
U.S. Army photo by Sgt. Joe Padula, 2nd BCT PAO, 101st Abn. Div.