Lage Manufacturing have uploaded new videos of their long-in-development-not-for-sale prototype machine gun / shotgun patterned after the famous M-41A Pulse Rifle (from the Aliens movies). The MAX-41A incorporates an unmodified M-11/9 lower receiver (registered machine gun) and a Remington 870 short barreled shotgun. It holds 50 rounds of 9mm and 2+1 rounds of 12 gauge.

Thanks to Robert for the tip.