The Aero Precision M4E1 Assembled Lower is a partially assembled lower receiver for AR-15 rifles, offering a reliable and convenient foundation for firearm builds. As an assembled lower, it includes pre-installed components such as the takedown and pivot pins, bolt catch, magazine release, and safety selector, simplifying the assembly process. However, it does not include the fire control group (trigger assembly), buffer system, or stock, allowing builders to select these parts according to their preferences. Machined from high-quality 7075-T6 aluminum, the M4E1 Assembled Lower features an integrated trigger guard for enhanced durability and a flared magazine well for faster and easier reloads. The receiver is precision-machined to Mil-Spec dimensions, ensuring compatibility with a wide range of AR-15 components. Finished with Type III hardcoat anodizing, it offers superior corrosion resistance and durability. Threaded bolt catch roll pins simplify assembly, making the M4E1 Assembled Lower a user-friendly and robust choice for AR-15 enthusiasts seeking flexibility and reliability.