The PMAG(R) 20 AR 300 B GEN M3(TM) is a purpose-designed magazine for rifles chambered in 300 Blackout(R). 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. In addition to the performance gained by a dedicated mag, the PMAG 20 AR 300 B also offers a safer way to feed your 300 Blackout rifle. When using 5.56x45mm mags, the potential to chamber and fire a 300 Blackout round in a 5.56x45mm rifle with catastrophic results requires diligent ammunition management by the shooter. The PMAG 20 AR 300 B's distinct rib design and smoother upper-half texture provides the shooter a distinct visual and tactile difference from any other PMAG to mitigate dangerous cross-loading issues.