This is a TacStar Side Saddle, model 1081157.
The patented TacStar Sidesaddle mounts extra rounds on your shotgun in a convenient and accessible location for fast reloading. The tough" weatherproof shell carrier is attached to an aluminum mounting plate that installs directly on the shotgun receiver. All mounting screws are included.
Features:
Corrosion Resistant Polymer Shell holder
Rugged, Aluminum Backing Plate
Easy Mounting