High-capacity aftermarket magazines for AR-15 style rifles manufactured by Schmeisser and imported by American Tactical INC (ATI). The magazines are built using heavy-duty fiberglass polymer and feature a high-capacity, quad-stack design allowing for up to 60 rounds to be carried while retaining a classic magazine profile for better compatibility with magazine pouches and carriers compared to drum-style magazines. A unique two-piece follower ensures reliable feeding while the ribbed texture on the walls of the magazine ensure a firm grip even under high stress environments. The Generation 2 series features a more reliable bolt hold open engagement mechanism along with a viewport to allow the user to keep track of their remaining ammunition. These magazines are chambered for 5.56x45mm NATO and .223 Remington ammunition only and are not compatible with .300 AAC Blackout ammunition.