This is a TacStar known as the Stock Adapter, model 1081230.
TacStar's Stock Adapters are designed to allow the use of any AR-15 type telescoping stocks and pistols grips on your shotgun. Unlike some competitive polymer adapters" TacStar's are made of a tough die cast metal alloy which not only provides greater strength" but also additional weight to reduce felt recoil. Designed to perfectly match the factory receiver contours and mount up seamlessly. The adapters are designed for proper drop to use bead or ghost ring sights. The adapters will accept any standard AR-15 grip without a beavertail" or one having a flexible rubber beavertail" such as Pachmayr" Ergo and some Hogue grips. The adapter also features QD sling attachment ports on both sides. (Does not include buffer tube or stock).
Features:
Die-cast metal alloy design
Accepts most AR-15 grips and buffer tubes