Mil-Standard Complete SA-4 Non-Folding Lower (BLEM)

A Complete AR-15 Lower Built the Right Way

The Shield Arms Mil-Standard Complete SA-4 Non-Folding Lower gives AR-15 builders and shooters a professionally assembled lower receiver that skips the guesswork and gets them running. At its core is the SA-4 billet lower receiver—CNC-machined from 7075-T6 aircraft-grade aluminum with mil-spec dimensions and finished to Mil 8625 Type 3 Class 2 hard-coat anodizing—paired with a proven mil-standard trigger, A2 grip, A2 stock, and mil-spec safety selector. Every component meets or exceeds military specification, delivering the reliability, interchangeability, and longevity that mil-spec standards were designed to guarantee.

Whether you're completing your first AR-15 build, replacing a worn lower, or stocking a reliable training rifle, the SA-4 Non-Folding Complete Lower is the straightforward answer. Drop on your preferred mil-spec upper receiver, and you're done. No fitting, no gunsmithing, no compatibility questions. This is a working rifle lower—built in the USA, and assembled to the standard that military, law enforcement, and serious civilian shooters have trusted for years.

For shooters who want a no-frills, professionally built AR-15 lower that just works, the Mil-Standard Complete SA-4 Non-Folding Lower is the answer. Proven components. Tight tolerances. American manufacturing. Zero compromises.

Key Features

• SA-4 Billet Lower Receiver: CNC-machined from 7075-T6 aircraft-grade aluminum billet with mil-spec dimensions—tighter fitment and improved consistency compared to standard forged or cast lowers, and marked "MULTI" for maximum caliber flexibility
• Mil 8625 Type 3 Class 2 Hard-Coat Anodized Finish: Matte black hard-coat anodizing to the military standard for aluminum finish—exceptional wear resistance, corrosion protection, and consistent appearance through years of hard use
• Upper Tension Screw: A threaded hole behind the grip screw accepts the included hardware, allowing you to dial out any vertical slop between upper and lower without aftermarket accessories—a feature rarely found at this price point
• Threaded Bolt Catch Pin: Threaded bolt catch pin hole with hardware included eliminates the roll pin punching that plagues standard lower builds, making assembly and future service significantly easier
• Precision Beveled Magazine Well: Machined mag well with beveled feed lip provides faster, more reliable magazine changes—accepts all standard AR-15 magazines
• Mil-Standard Trigger Group: A proven, mil-spec trigger providing consistent pull weight, reliable reset, and the durability to handle high round counts across years of training and field use
• A2 Grip: The original mil-spec grip profile—durable, ergonomic, and compatible with virtually every AR-15 accessory on the market
• A2 Stock: Fixed A2 buttstock delivers a solid, consistent cheek weld and length of pull with a rugged design that withstands hard use in any environment
• Mil-Standard Safety Selector: Mil-spec safety selector with positive detent engagement and clear Safe/Fire position feedback
• Broad Parts Compatibility: Compatible with most standard AR-15 components and the majority of aftermarket parts—build it your way without compatibility headaches
• Made in USA: Manufactured in Bigfork, Montana, with American materials and precision CNC machining throughout

What Does "Mil-Standard" Mean?

Military Specification (Mil-Spec): When components are described as "mil-standard" or "mil-spec," they meet the dimensional, material, and performance standards established by U.S. military procurement specifications for the M16/M4 platform. This matters because mil-spec components are manufactured to consistent tolerances, ensuring reliable interchangeability across thousands of AR-15 and M4-pattern rifles and components from different manufacturers. Mil-spec is the industry benchmark—not a marketing term—and it means your trigger group, safety selector, and stock will fit, function, and interchange with any other mil-spec AR-15 component without modification.

Mil 8625 Type 3 Class 2 Anodizing: The SA-4's hard-coat anodized finish meets MIL-A-8625 Type III Class 2—the same anodizing specification used on U.S. military aluminum components. Type III hard-coat anodizing is significantly more wear-resistant than standard Type II anodizing, providing a surface hardness comparable to case-hardened steel and corrosion protection that holds up in any operating environment.

Technical Specifications

Performance Advantages

Builder-Friendly Design Details That Matter

The SA-4's threaded bolt catch pin hole is one of those features that builders notice immediately. Standard AR-15 lowers use a roll pin for the bolt catch, which requires a punch, a block, and patience—and often leaves cosmetic marks on the lower during assembly. The SA-4's threaded design eliminates that entirely, making assembly and future service significantly easier and cleaner. Combined with the precision beveled magazine well for faster reloads and the upper tension screw for fit adjustment, the SA-4 is engineered with the builder and the end user in mind.

Mil-Spec Reliability Built In

Every component in this complete lower—trigger, safety, grip, stock—meets mil-spec standards. That means consistent pull weights, positive safety engagement, and parts that interchange with any mil-spec AR-15 component in your inventory. For training builds, duty rifles, or range workhorses that need to run hard and be easily serviced, the mil-spec foundation of this complete lower is a feature, not a compromise.

Ready to Run with Any Mil-Spec Upper

Because the SA-4 lower is assembled to mil-spec tolerances, it mates directly with any standard mil-spec AR-15 upper receiver without fitting or modification. Whether you're pairing it with a Shield Arms upper, a factory upper from a major manufacturer, or a precision custom upper, the SA-4 complete lower provides a rock-solid foundation that installs in seconds.