Aero Precision APAR600033C: The M4E1 PRO lower receiver is the next evolution of the M4E1 lineup. Machined from a solid 7075-T6 forging- this lower receiver is fully ambidextrous and seamlessly incorporates mirrored controls into the construction of the lower allowing for a reliable and intuitive user experience. All proprietary componentry of this lower receiver comes preinstalled and is compatible with mil spec parts and components giving the builder the freedom to configure as they see fit. Includes: M4E1 Stripped Lower Receiver - Anodized Black Bolt Catch Assembly Magazine Release Assembly