M26 MASS (Modular Accessory Shotgun System)

Available from Morphys here:
https://auctions.morphyauctions.com/_N__VERTU_CORP_C_MORE_COMPETITION_M26_MASS_12_GAUG-LOT661207.aspx

The M26 Modular Accessory Shotgun System (MASS) was designed by C-More Products company as a new shotgun option for the US military. First prototyped in 1999, it was not actually adopted until 2012, but had been purchased in significant numbers since then. The idea is that the M26 can function as either a standalone weapon or attached under the barrel of an M4 Carbine, thus replacing a couple of different items in inventory. It weighs just 3.5 pounds in the under barrel configuration, significantly less than the Masterkey system, and is much more convenient for a breacher to carry than an M4 along with a separate Mossberg 500.

The M26 is a bolt-action 12ga shotgun that feeds from both 3- and 5-round magazines. It has folding integrated aperture sights and is envisioned for use in a wide variety of roles. Military ammunition supplies include #7.5 and #9 birdshot, classic #00 buckshot, rubber buckshot, rubber slugs, and breaching rounds (powdered metal in a wax binder). For use with breaching, the M26 includes a retractable breaching muzzle device.