The PMAG 30 AR 300 B GEN M3 is a purpose-designed magazine for rifles chambered in 300 Blackout. Since its inception, 300 Blackout shooters have had to use a magazine designed for another cartridge, limiting its ultimate performance and compatibility. One of the nice features of 300 Blackout 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 Blackout magazine was a logical step for the PMAG line