This is a Ergo Grip , model 4453.
Use ERGO's Remington 870 Stock Adapter to install AR-15 type stocks and pistol grips on your Remington shotgun. It can be used to shorten the length of pull on your favorite scattergun to a more manageable length.
Features:
Accepts any standard AR-15 buffer tube and grip
Has the proper drop designed in so factory sights can be used;Includes mounting hardware
