The PMAG 30 AR 300 B GEN M3 is a purpose-designed magazine for rifles chambered in 300 BlackoutA(R) (300 BLK). Since its inception, 300 BLK shooters have had to use a magazine designed for another cartridge, limiting its ultimate performance and compatibility. One of the key features of 300 BLK is the compatibility with 5.56x45mm parts, but with the magazine, it is a compromise to do so. Due to the wide variety of projectile weights and profiles potentially decreasing overall reliability, a dedicated 300 BLK magazine was a logical step for the PMAG line. In addition to the performance gained by a dedicated mag, the PMAG 30 AR 300 B also offers a safer way to feed your 300 Mfg: Magpul