The 5.56/.223/.300BLK DURAMAG SS is designed for serious shooters who require the most out of their magazines so when performance and durability are paramount, make the switch to DURAMAG SS(TM) and never look back. Constructed from premium 410 Stainless Steel for maximum durability. This material, coupled with advanced interior and exterior geometries, ensure ultimate reliability and feeding. DURAMAG will not flex or swell like polymer and are safe for extended storage while loaded without any add ons. These magazines utilize our T-360 coating to ensure not only incredibly smooth performance and ease of loading, but also product longevity through the harshest conditions. These are the ultimate magazine of choice for shooters that are running 300 Blackout especially round with long load length or even the heaviest of sub-sonic loads.