This is a Ergo Grip Rubber known as the Sure Grip, model 4045BK.
The ERGO AR15/M16 Tactical Deluxe Suregrip is a larger more rounded grip than the original Ergo Grip providing exceptional comfort and control for those with medium to large hands. This grip features hand filling palm swells for both left and right handed shooters. Rubber over molded grip with an integral rear upper extension that provides the web of your hand additional support; the textured finish provides a positive grip even when wearing gloves. Uses the existing hardware that is already present on your rifle's grip.
Features:
Fits AR-15/AR-10 type firearms in .223 and .308
Over molded SUREGRIP material with heavy texture
Ambidextrous palm swell
Fits medium to large hands