This is the Lancer L7AWM .308/7.62x51mm 10 Round Translucent Magazine from Lancer Systems. The Lancer L7AWM fits AR-10/SR-25-styled rifles chambered in .308 WIN or 7.62x51mm.

The L7AWM is short for L7 Advanced Warfighter Magazine, as it was designed to be the ultimate AR-10/SR-25 magazine for military, law enforcement, and competition. This magazine is compliant in States that require a magazine capacity of 10 rounds or less.

Being the first true steel/polymer hybrid magazine, the Lancer AMW features a hardened steel lip assembly and anti-tilt follower, with an advanced polymer construction. This .308WIN / 7.62NATO magazine offers the reliability and endurance of traditional steel magazines, while still offering the weight and maneuverability of advanced, light polymer. 

Moving on, its advanced polymer body offers micro-stipple pyramids for excellent grip and control. And at the bottom, it offers a L7AWM baseplate for quick access to internals for cleaning if desired.