This is a ALUMINUM 30-round magazine for AR-15 rifles in 300 AAC BLACKOUT.
D&H Tactical aftermarket magazines transcend the industry standard for AR-15/M4 magazines. Thanks to their cutting-edge robotic manufacturing technology and commitment to using only the highest quality All-American materials, D&H delivers the ultimate magazine—every time.
Lightweight, affordable, and manufactured 100% in the U.S.A. D&H magazines are made from 6061 T6 aluminum, 17-7PH stainless springs pre-compressed and passivated for ultimate consistent performance and a long service life. 
D&H uses a proprietary limited tilt follower in red that will not get stuck and will assure you stay solid and smooth at the range.
Keeping a few extra factory magazines around is never a bad idea; extra magazines save loading time at the range and also serve as a backup for those days when you simply cannot remember where you put your primary magazine.