Lage Manufacturing made this one off Aliens M41A Pulse rifle. It is a M-11 in 9mm shoved into the body of a M41A Pulse Rifle. They used a Remington 870 AOW/SBS for the grenade launcher portion of the Pulse Rifle. The actual movie prop was based off a Thompson M1A and a Franchi SPAS 12 shotgun. I don’t care what the Lage MFG pulse rifle is made of. It looks really cool and the round counter works. I would love a semi auto version of this.
Source: The Firearm Blog