The AR15 Mil-Spec Blueprint is a detailed, precise diagram that outlines the specifications and dimensions for building or inspecting AR15 lower receivers according to military standards. This blueprint serves as a valuable resource for ensuring that your AR15 components meet the expected tolerances for reliable performance and compatibility. However, it is important to note that not all “mil-spec” lower receivers are manufactured to the exact same standards. Variations in machining processes and quality control can lead to discrepancies in certain dimensions, even when the parts are labeled as mil-spec. Always verify the specific manufacturer’s tolerances and ensure your components align with the blueprint for optimal functionality and safety.