This is a Magpul Industries known as the Enhanced AR Mag Release chambered in 223 Remington, model MAG568-BLK.
The Magpul AR Enhanced Magazine Release provides an enlarged contact surface for quick and fumble free magazine changes. With easy bolt-on installation with no gunsmithing required" the Enhanced AR Magazine Release is made of Mil-Spec hard anodized aluminum to provide durability and light weight. Made in U.S.A.
Features:
Machined from milspec anodized aluminum
Provides larger contact surface for positive activation
Compatible with most 5.56 and 7.62 pattern receivers
