AR-15 Lower Receivers

Stripped vs. Complete Lower: Which Should You Buy?

A stripped lower is the bare serialized receiver with no internal components — the starting point for a custom build where you select and install every trigger, grip, stock, and fire control group yourself. A complete lower comes with all lower parts installed (trigger group, safety, grip, stock, buffer tube, and buffer) and is ready to accept an upper receiver. For first-time builders, a complete lower from a reputable manufacturer eliminates the complexity of sourcing and fitting lower parts kits. For experienced builders who want to specify every component, a stripped lower gives maximum control.

Mil-Spec vs. Billet Lower Receivers: Understanding the Difference

Mil-spec AR-15 lower receivers are forged from 7075-T6 aluminum to military specifications — the same material and process used in military M4 carbines. Forged lowers are the most proven design, with excellent strength-to-weight ratio and consistent dimensions that guarantee compatibility with any mil-spec upper. Billet lowers are machined from a solid block of aluminum (typically 7075-T6 as well) rather than forged, allowing more complex shapes, tighter tolerances, and aesthetic features like integrated trigger guards and distinctive profiles. Billet lowers are heavier and more expensive but offer premium fit-and-finish. For a practical build, forged mil-spec is the right choice.

Best AR-15 Lower Receiver Brands: Aero Precision, Anderson & More

Aero Precision is the most popular aftermarket lower receiver brand — their M4E1 lower features a threaded bolt catch roll pin hole (eliminating the most frustrating step in lower assembly), a built-in trigger guard, and tight mil-spec tolerances that pair well with any upper. Anderson Manufacturing produces the most affordable forged lowers that reliably meet mil-spec dimensions. Geissele produces premium forged and billet lowers as part of their Super Duty line. For budget builds, Anderson; for best all-around value, Aero Precision; for premium builds, Geissele or Noveske.

AR-15 Lower Parts Kit: What’s Inside and What to Upgrade

A standard lower parts kit (LPK) includes the trigger and hammer with mil-spec springs, disconnector, safety selector, bolt catch, magazine release, takedown and pivot pins, grip, and all associated springs and detents. The trigger group is the component most worth upgrading — mil-spec triggers typically break at 6–8 lbs with significant creep. A drop-in replacement from Geissele transforms the feel of any AR-15 for $150–$300. Other LPK components are largely interchangeable; mil-spec parts from reputable manufacturers like Spike’s Tactical, Daniel Defense, or Aero Precision are all equivalent in quality.

AR Pistol Lower Receivers: What Makes a Lower “Pistol”

An AR-15 lower receiver becomes a “pistol lower” when it is built as a pistol from the start — fitted with a pistol brace rather than a rifle stock, with a barrel under 16″. A lower that has ever been built as a rifle cannot legally be converted to a pistol configuration. If you intend to build an AR pistol, start with a stripped lower that has never had a stock attached. Since January 1, 2026, the NFA $200 tax stamp has been eliminated, making short-barreled rifle (SBR) registration via Form 1 a straightforward option if you prefer a traditional stock on a short barrel.

Frequently Asked Questions: AR-15 Lower Receivers

Is an AR-15 lower receiver a firearm?
Yes — the AR-15 lower receiver is the serialized component that is legally classified as the firearm under the Gun Control Act. All other AR-15 components (upper receiver, barrel, handguard, stock) are unregulated parts. Purchasing a stripped lower receiver requires the same FFL transfer process as purchasing a complete firearm — a Form 4473 background check through a licensed dealer. Complete lower receivers (with trigger group and stock installed) are also transferred through an FFL.

What is the difference between a stripped and complete lower?
A stripped lower is just the lower receiver casting or forging — no trigger group, no grip, no stock. The buyer installs all lower parts (LPK — Lower Parts Kit) themselves. A complete lower has everything installed below the upper: trigger group, pistol grip, and stock or pistol brace. A complete lower attached to an upper is a fully functional rifle. For builders who want to choose their own components, stripped lowers are the starting point; for buyers who want to complete a rifle quickly without assembly, a complete lower is more practical.

What materials are AR-15 lowers made from?
Most production AR-15 lowers are forged 7075-T6 aluminum — the mil-spec standard. Billet lowers are machined from a solid aluminum block and allow more design freedom at higher cost. Polymer lowers (Aero Precision, Plum Crazy) are lighter and less expensive but generally considered less durable under sustained hard use. For a standard defensive or sporting rifle, forged 7075-T6 aluminum is the appropriate choice.

See Also: AR-15 Rifles • AR-15 Uppers • AR-15 Parts • Triggers • Aero Precision