This is a Magpul Industries Forend known as the Hunter X-22 Takedown Forend, model MAG1065-BLK.
The Hunter X-22 Takedown Forend is intended for use with additional barrels on rifles currently equipped with the Hunter X-22 Takedown Stock. Made from high quality reinforced polymer" the X-22 Takedown Forend features a reversible barrel tray" ensuring proper fit for factory pencil profiles as well as heavy bull barrels with up to 0.920" outer diameter. It features multiple M-LOK(R) slots for accessory attachment and an adjustable barrel-tensioning shim in the forend for setting barrel preload (the barrel may also be free-floated). It also includes a dimpled drill point at the bottom of the forend for installation of sling swivel studs for bipod or sling swivel us
Features:
M-LOK® slots on forend sides and bottom
Reinforced polymer construction for strength and durability
Easy exchange of different barrels for the same rifle