Why the Lower Receiver Matters
The lower receiver is legally the firearm in an AR-15 system. It’s the serialized component that houses the fire control group, accepts the magazine, and connects to the buffer tube and stock assembly. While the upper receiver, barrel, and bolt carrier group may get more attention from accuracy enthusiasts, the lower receiver is the foundation that everything else depends on.
Choosing the right lower receiver affects your rifle’s trigger feel, magazine compatibility, ergonomics, and overall build quality. It’s a decision worth getting right from the start.
Stripped Lower Receivers
A stripped lower is just the machined receiver body with no internal parts installed. This is the choice for builders who want complete control over every component in their trigger group, grip, and stock selection. Stripped lowers typically cost between $50 and $300 depending on the manufacturer, material, and features.
Building from a stripped lower allows you to select exactly the trigger, safety selector, bolt catch, magazine release, and buffer assembly you want. It also provides an educational experience that deepens your understanding of how the AR-15 functions. For experienced builders, a quality stripped lower and carefully selected components often yield a better rifle than many factory complete options.
Complete Lower Receivers
A complete lower comes fully assembled with the fire control group, pistol grip, buffer tube, buffer, buffer spring, and stock already installed. This option simplifies the build process to a single step: attach the upper receiver with two pins. Complete lowers are ideal for builders who want to focus their attention and budget on the upper half while getting a reliable, professionally assembled lower.
Factory complete lowers from reputable manufacturers ensure proper torque specifications on the castle nut, correct staking, and quality-checked component fit. For first-time builders, this removes the most common sources of assembly errors.
Forged vs Billet Aluminum
Most AR-15 lower receivers are made from 7075-T6 aluminum, but the manufacturing method differs significantly between forged and billet options. Forged lowers start as a rough shape created by forcing heated aluminum into a die under extreme pressure. This process aligns the metal’s grain structure, creating a very strong part. The forging is then machined to final specifications. Forged lowers are the military standard and generally offer the best strength-to-cost ratio.
Billet lowers are machined entirely from a solid block of aluminum on CNC machines. This process allows more creative design features like integrated trigger guards, unique aesthetics, and tighter tolerances. Billet lowers are typically more expensive but offer a premium look and feel that many builders appreciate.
Polymer and Alternative Materials
Polymer lower receivers have improved dramatically in recent years. Modern reinforced polymer lowers offer significant weight savings and adequate durability for most applications. However, they remain controversial among serious shooters. The buffer tube mounting area and takedown pin holes are stress points where polymer can fail under heavy use. For a dedicated range rifle or lightweight build, quality polymer lowers are viable. For a duty or defensive rifle, aluminum remains the standard.
Key Specifications to Check
Regardless of which type you choose, verify these critical specifications: proper mil-spec dimensions for the trigger pin holes (0.154 inches), correct magazine well dimensions for reliable feeding, proper buffer tube threading, and a quality Type III hard-coat anodized finish for corrosion resistance. At G2 Precision, every lower receiver meets or exceeds mil-spec requirements because there’s no room for compromise in the foundation of a precision rifle.
Making Your Choice
For most builders, a quality forged stripped lower from a reputable manufacturer provides the best starting point. It gives you control over component selection while keeping costs reasonable. If you prefer simplicity, a complete lower with a good mil-spec trigger is a reliable foundation that you can upgrade over time as your preferences develop.
