The SGM Tactical® .45 ACP 10-Round Extended Magazine for Glock 21 Pistols is a performance-enhanced aftermarket centerfire pistol magazine designed to deliver factory-like performance at a low, budget-friendly price. Constructed of an advanced polymer with a full-length, heat-treated steel lining, this SGM Tactical Glock-pattern pistol magazine is manufactured using computer-assisted design technologies for superior performance and reliability.