The Magpul PMAG M3 300 B is a purpose-built AR-15 magazine engineered specifically for .300 Blackout ammunition. Unlike generic 5.56×45mm magazines that compromise reliability and safety when pressed into duty for subsonic rounds, this dedicated .300 Blackout magazine gives you the performance and peace of mind that caliber deserves. It's the smart choice for anyone running a 300 BLK AR platform rifle, whether you're building a short-barreled upper, a precision subsonic setup, or a dedicated hunting rifle.

The 20-round capacity strikes a practical balance: compact enough for maneuverability in tight spaces and easier to carry than a 30-rounder, yet substantial enough for serious shooting sessions. Magpul engineered this magazine with a distinctly ribbed design and textured upper half that visually and tactilely sets it apart from standard PMAGs—a deliberate safety feature that helps eliminate the dangerous possibility of accidentally loading .300 Blackout into a 5.56 rifle. If you've ever worried about cross-loading ammunition between platforms, this magazine design eliminates that risk at the source.

Built with Magpul's proven Gen M3 polymer construction, the PMAG 300 B handles impact and crushing forces without sacrifice to feeding reliability. It features aggressive front and rear texture for confident handling even with gloved hands, a removable slim floor plate for easy cleaning and maintenance, a paint pen dot matrix printed on the body for your own marking and identification, and a dust/impact cover to keep the rounds and feed lips protected in the field. Made in the USA, this is the magazine that lets your .300 Blackout rifle perform as designed.