This is the ETS Group AR-15 Gen 1 30-round magazine in .223 Remington / 5.56x45mm NATO.

ETS’s AR15 magazine features a no tilt follower with reliable bolt open on the last round. It has a clip on the dust cover to keep dirt and debris out during storage. The AR mag also has fast and easy disassembly for maintenance without tools via ETS’s specially designed floor plate. The ergonomically designed floorplate makes it easy to grab from mag pouches.