These standard capacity magazines are designed to hold 30 rounds of .223 Remington or 5.56A-45. Lightweight, they are made from 6061-grade aluminum. They are heat-treated and anodized per MIL-A-8625 Type III Class I for durability. Specifications Weight: 0.3lbs Compatibility: AR-15 / M16 / M4 Caliber: .223 / 5.56x45mm Capacity: 30 Rounds Body Material: Aluminum Spring Material: Stainless Steel Finish: Anodized