The PMAG AR 300 B GEN M3 is a purpose-designed magazine for rifles chambered in 300 Blackout. Since it's inception, 300 Blackout shooters have had to use a magazine designed for another cartridge, limiting it's 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 shapes potentially decreasing overall reliability, a dedicated 300 Blackout magazine was a logical step for the PMAG line. In addition to the performance gained by a dedicated mag, the PMAG AR 300 B also offers a safer way to feed your 300 BLK rifle. When using 5.56 mags, the potential to chamber and fire a 300 BLK round in a 5.56 rifle with catastrophic results requires diligent ammunition management by the shooter. The PMAG AR 300 B's distinct rib design provides the shooter a distinct visual and tactile difference from any other PMAG to mitiga...