What is the SA-4 Complete Non-Folding Lower Receiver?
The SA-4 is a premium complete lower receiver assembly machined from 7075-T6 aircraft-grade billet aluminum, designed to be the perfect starting point for your AR-15 build. This complete unit comes equipped with quality components including a B5 Systems Bravo stock, B5 Type 22 grip, ALG Advanced Combat Trigger, and Radian safety selector—eliminating the need to source individual parts.
Complete your build with these popular accessories:
Premium Billet Lower Receiver Built for Performance
The SA-4 Complete Non-Folding Lower Receiver represents the pinnacle of precision manufacturing and thoughtful component selection. Unlike forged receivers that rely on stamping and forming processes, this billet lower is CNC-machined from a solid block of 7075-T6 aircraft-grade aluminum, ensuring superior dimensional consistency and structural integrity. Every surface, radius, and angle is precisely controlled to deliver true mil-spec dimensions that guarantee compatibility with virtually any upper receiver and aftermarket components you choose.
What sets the SA-4 apart is not just the exceptional lower receiver itself, but the carefully selected components that come pre-installed. The B5 Systems Bravo stock offers a perfect balance of strength and weight savings, while the B5 Type 22 grip provides excellent ergonomics for extended shooting sessions. The ALG Advanced Combat Trigger delivers a crisp, reliable trigger pull that enhances accuracy without compromising reliability. The Radian safety selector adds ambidextrous functionality with its smooth, positive engagement. This complete assembly saves you the time and expense of sourcing individual components while ensuring compatibility and quality throughout.
Finished with a matte black hard-coat anodizing per Mil 8625 Type 3 Class 2 specifications, the SA-4 provides exceptional corrosion and wear resistance. The precision-machined magazine well features beveled feed lips that facilitate rapid magazine changes, while the threaded bolt catch pin and upper tension screw allow for precise adjustment of fitment—eliminating any play between upper and lower receivers. Marked with "MULTI" caliber designation, this versatile lower supports multiple caliber configurations, making it ideal for builders who want maximum flexibility in their AR-15 platform.
Key Features
- Premium Billet Construction: Machined from 7075-T6 aircraft-grade billet aluminum for superior strength and dimensional accuracy
- Complete Assembly: Includes B5 Systems Bravo stock, B5 Type 22 grip, ALG Advanced Combat Trigger, and Radian safety selector
- Precision Magazine Well: Beveled feed lips for rapid, fumble-free magazine changes
- Adjustable Upper Tension: Threaded upper tension screw behind grip allows elimination of any play between receivers
- Threaded Bolt Catch Pin: Threaded hole with included hardware for secure, anti-rotation installation
- True Mil-Spec Dimensions: Accepts all standard AR-15 magazines and components
- Durable Hard-Coat Anodizing: Matte black finish per Mil 8625 Type 3 Class 2 specifications
- Multi-Caliber Marking: "MULTI" caliber designation provides maximum build flexibility
Built with Quality Components
The SA-4 comes complete with premium components that would cost significantly more if purchased separately. The B5 Systems Bravo stock is a favorite among serious shooters for its reinforced polymer construction and storage compartment. The B5 Type 22 grip features an aggressive texture pattern and reduced angle for improved ergonomics. The ALG Advanced Combat Trigger is known for its smooth pull and positive reset, making it suitable for everything from precision shooting to tactical applications. The Radian safety selector provides ambidextrous operation with a short 90-degree throw and crisp engagement. Quality mil-spec castle nut and end-plate complete the assembly.
Technical Specifications
| Specification |
Details |
| Material |
7075-T6 Aircraft-Grade Billet Aluminum |
| Finish |
Matte Black Hard-Coat Anodized (Mil 8625 Type 3 Class 2) |
| Dimensions |
Mil-Spec |
| Caliber Marking |
MULTI |
| Magazine Compatibility |
All Standard AR-15 Magazines |
| Weight |
2.1 lbs (Complete Assembly) |
| Buttstock |
B5 Systems Bravo |
| Grip |
B5 Type 22 |
| Trigger |
ALG Advanced Combat Trigger |
| Safety Selector |
Radian Ambidextrous Safety |
| Upper Tension Adjustment |
Yes (Threaded Screw with Hardware Included) |
| Bolt Catch Pin |
Threaded (Hardware Included) |
Why Choose Billet Over Forged?
| Feature |
SA-4 Billet Lower |
Standard Forged Lower |
| Manufacturing Process |
CNC-machined from solid billet |
Forged and stamped |
| Dimensional Accuracy |
Extremely precise, consistent |
Varies by manufacturer |
| Upper Tension Adjustment |
Yes, threaded screw included |
Typically no |
| Threaded Bolt Catch |
Yes, prevents rotation |
Standard pin only |
| Magazine Well |
Precision beveled feed lips |
Standard dimensions |
| Components Included |
Premium B5, ALG, and Radian parts |
Varies or none |
Frequently Asked Questions
What upper receivers are compatible with the SA-4 lower?
The SA-4 features true mil-spec dimensions and will accept virtually any mil-spec AR-15 upper receiver. The included upper tension screw allows you to eliminate any play between the upper and lower, ensuring a perfect fit regardless of which upper you choose.
Does this lower come with a lower parts kit?
Yes, the SA-4 is a complete lower receiver assembly. It includes all internal components: trigger (ALG Advanced Combat Trigger), safety selector (Radian ambidextrous), grip (B5 Type 22), stock (B5 Systems Bravo), buffer tube, buffer, and spring. You only need to add an upper receiver, barrel, bolt carrier group, and charging handle to complete your build.
Can I use this lower for a pistol build?
The SA-4 is equipped with a rifle-length stock and is designed for rifle configurations. If you're planning a pistol build, you would need a pistol-designated lower receiver without a stock attached. Check current ATF regulations before modifying or converting any receiver.
What is the advantage of the threaded bolt catch pin?
The threaded bolt catch pin prevents rotation and potential loosening over time—a common issue with standard roll pins. The threaded design ensures a secure, permanent installation while making installation and removal easier if needed for maintenance or upgrades.
How do I adjust the upper tension screw?
The upper tension screw is located behind the grip screw. After installing your upper receiver, if you notice any play or looseness between the upper and lower, simply tighten the tension screw using the included hardware until the fit is snug. This allows you to achieve a perfect, rattle-free fit with any upper receiver.
What calibers can I build with this lower?
The SA-4 is marked "MULTI" and accepts any caliber that uses the standard AR-15 platform. This includes .223 Remington/5.56 NATO, .300 Blackout, 6.5 Grendel, 6.8 SPC, .350 Legend, and many others. The versatility of the MULTI marking provides maximum flexibility for current and future builds.
Is the ALG trigger adjustable?
The ALG Advanced Combat Trigger is a non-adjustable, mil-spec style trigger designed for reliability and improved performance over standard triggers. It features a smooth pull and positive reset suitable for combat, competition, and recreational shooting.
What magazines work with this lower?
The SA-4 accepts all standard AR-15 magazines including PMAG, USGI aluminum magazines, Lancer magazines, and others. The precision-machined magazine well with beveled feed lips works seamlessly with any AR-15 compatible magazine.
Can I replace the stock or grip?
Yes, both the B5 Systems Bravo stock and B5 Type 22 grip use standard mil-spec attachment points. You can replace either component with any aftermarket AR-15 stock or grip, though the included B5 components are among the highest quality available.
What is the difference between billet and forged lowers?
Billet lowers are CNC-machined from a solid block of aluminum, allowing for tighter tolerances, custom features like the threaded bolt catch and upper tension screw, and superior dimensional consistency. Forged lowers use a stamping process that is faster but may have more dimensional variance. The SA-4's billet construction ensures precision and reliability.
Does this lower come with a warranty?
Yes, the SA-4 Complete Lower Receiver is backed by Shield Arms' 100% lifetime warranty. We stand behind the quality and durability of our products with complete confidence.
Is this lower receiver made in the USA?
Absolutely. The SA-4 is proudly designed, machined, and assembled in the United States using American-made materials and components. Shield Arms manufactures all our receivers domestically to ensure the highest quality standards.
Who Should Buy the SA-4 Complete Lower Receiver?
- AR-15 Builders: Those starting a new build who want a premium foundation with quality components already installed
- Precision Shooters: Marksmen who demand tight tolerances and the ability to eliminate any play between receivers
- Tactical Shooters: Operators who need reliable, combat-proven components like the ALG trigger and Radian safety
- Competition Shooters: Competitors who appreciate the smooth trigger pull and precision machining for consistent performance
- First-Time Builders: New builders who want to avoid the complexity of sourcing and assembling individual lower parts
- Collectors: Enthusiasts who appreciate the craftsmanship and quality of American-made billet receivers
- Upgrade Seekers: Shooters looking to replace a basic forged lower with a precision billet unit featuring premium components
Made in USA with Lifetime Warranty
The SA-4 Complete Non-Folding Lower Receiver is proudly manufactured in the United States using premium American materials. Every receiver is precision-machined to exacting standards and undergoes rigorous quality control before shipping. Shield Arms backs this product with our 100% lifetime warranty—if there's ever an issue with your SA-4 lower due to materials or workmanship, we'll make it right. When you choose Shield Arms, you're investing in American craftsmanship, quality components, and peace of mind that lasts a lifetime.
Complete Your AR-15 Build
The SA-4 provides the perfect foundation, but you'll want to pair it with quality accessories for a complete setup. Consider these popular additions:
For additional guidance on completing your build, visit our installation guides and resources for helpful tips and detailed instructions.
