There are quite a few shotguns already in Aliens: Colonial Marines, but none of them are double barreled. The Sawed-off Double Barreled Shotgun is in your inventory at the start of the game. You won’t get to use them in the Stasis interrupted DLC. After each pull of the trigger, you need to reload it. If the DLC allowed you to upgrade the weapon like other weapons in the standard game, it might cut down on the reload time.
I can’t even say the shotgun is that much better than other shotguns already in the game. You can already kill most aliens with one pull of the trigger from any shotgun. The constant reload feels like a handicap better suited for more skilled players. While testing the weapon in the firing range, I found it did have a wide blast radius, but the other shotguns have a wide radius too.
Its just another shotgun that can’t be customized and upgraded like the others.