Ammunition Storage Component’s AR-15/M4/M16 Stainless Steel SPC magazines are built with the highest quality to ensure durability guaranteed! Their magazines are completely manufactured in the USA from start to finish, using ,.020″ gauge 410 Stainless-Steel Alloy that is heat-treated for added strength and durability. The stainless steel construction prevents swelling in heat and cracking in cold weather, providing a more reliable alternative to polymer magazines. All this is achieved while maintaining a sleek appearance.