This is a Magpul Industries Stock known as the MOE, model MAG404-BLK.
The MOE Rifle Stock (Magpul Original Equipment) is a drop-in replacement for AR15/M16 A1 and A2 rifle stocks utilizing the standard rifle-length receiver extension (buffer tube). Designed as a basic upgrade" the stock features integral 1.25" sling loop" optional dual-side front and rear QD mounting points" replaceable anti-slip rubberized butt-pad" and internal storage compartment accessible through the rear storage door.
Features:
The MOE Rifle Stock is a direct replacement for an A1 or A2 fixed stock
Can be fitted to carbine with additional parts