This is a Magpul Industries Stock known as the Buttpad, model MAG350-BLK.
The PRS Extended Rubber Buttpad" 0.80" replaces the standard rubber buttpad" adding approximately 0.50" to the original length of pull. Compatible with PRS AR15/M16 and AR10/SR25 models as well as the MOE(R) Rifle Stock and MOE(R) Fixed Carbine Stock. Mounts with existing hardware.
Features:
Made in the U.S.A.
Utilizes existing hardware
Rubber Material