The PMAG 20 AR 300 B GEN M3 is a purpose-built magazine for rifles chambered in .300 Blackout (300 BLK). Similar in every way to the PMAG 30 AR 300 B, the PMAG 20 is more compact for increased maneuverability and creates a more concealable package for use in small format firearms. Product Specifications Manufacturer: Magpul Model: SR15, M4, M16 Caliber: 300 Blackout Magazine Capacity: 20