Bushmaster 0020010BLK M4 Built Lower Receiver

The Bushmaster M4 Built Lower Receiver (model 0020010BLK) is a fully assembled, FFL-regulated component that serves as the serialized foundation for modern sporting rifle builds. This lower receiver is designed for shooters, armorers, and tactical professionals who demand a mil-spec platform capable of accepting standard M4/AR-15 upper assemblies. As a registered firearm component, the built lower comes ready for immediate integration into your rifle configuration without additional machining or fitting work.

Built to military specifications, the Bushmaster lower receiver features a rigidly-machined aluminum construction that ensures dimensional consistency and reliable cycling across field and tactical environments. The integrated trigger assembly pocket, magazine well, and control group housing are precision-finished to mil-spec tolerances, enabling seamless compatibility with any standard AR-15 upper receiver assembly. The black anodized finish provides durable corrosion resistance and reduced light reflection—critical for duty and precision applications. Weighing 2.92 pounds, the lower receiver distributes weight efficiently and works in concert with properly-matched upper assemblies to achieve balanced rifle ergonomics.

Law enforcement, military personnel, and civilian shooters rely on Bushmaster lower receivers for both patrol rifles and precision build platforms. The FFL designation means this component must be transferred through a licensed dealer—a safeguard that reflects its status as the regulated firearm portion of an AR-platform rifle. Installation requires a compatible upper receiver, charging handle, and bolt carrier group; all of which seat into the lower's standardized receiver extension and rail system. Whether you're building a 5.56 NATO duty rifle, a .308 Winchester precision platform, or a specialized tactical configuration, this Bushmaster lower provides the mil-spec foundation that professional and competitive shooters demand.