Stripped lower receiver for AR-style firearms manufactured by Aero Precision. The M4E1 series combines mil-spec dimensions with a sleek, updated design aimed at improving ergonomics while maintaining full compatibility with aftermarket parts. The receiver features a flared magwell for improved reloading ability along with an integrated trigger guard for greater overall strength. The PRO series seamlessly integrates ambidextrous controls into the receiver, allowing the user to easily manipulate all the vital controls without changing their grip. This model features an all-black finish. The receivers are multi-caliber rated and are compatible with standard mil-spec upper receivers and lower parts kits. This receiver includes the ambidextrous control parts but will require a lower parts kit to complete functionality.