What is the SA-9 Gen2 Folding Lower Receiver?
The Shield Arms SA-9 Gen2 is a revolutionary folding AR-15 lower receiver designed for 9mm pistol caliber carbine builds. Unlike bulky folding adapters, this lower features a built-in folding mechanism machined directly into the 7075-T6 billet aluminum body, accepting standard Glock double-stack magazines for a compact, reliable 9mm platform.
Build Requirements:
- Compatible with standard AR-15 upper receivers (9mm chambered)
- Accepts standard AR-15 fire control groups and furniture
- Uses Glock 17/19/34 pattern double-stack magazines
- Complete your build with premium accessories like the Mountain Partisan Sling
Revolutionary Folding Lower Receiver Technology
The SA-9 Gen2 represents Shield Arms' commitment to innovation in the firearms accessories industry. Built on our patented folding lower receiver system, this isn't just another AR-15 lower—it's a purpose-built 9mm platform that accepts Glock magazines while offering unprecedented portability. The integrated folding mechanism eliminates the need for bulky adapters or hinges, reducing overall length by approximately 8-10 inches when folded for storage or transport.
Precision-machined from 7075-T6 aircraft-grade billet aluminum and finished with matte black hard-coat anodizing per Mil 8625 Type 3 Class 2 specifications, the SA-9 Gen2 delivers the durability and reliability you expect from Shield Arms. The closed-bolt, blowback-operated design provides inherent accuracy and simplicity, while the beveled magazine well ensures lightning-fast reloads under pressure. At just 11.2 ounces, this stripped lower forms the foundation for a lightweight, compact 9mm carbine or pistol build.
Gen2 Improvements Over Original SA-9
The Gen2 update brings significant enhancements based on user feedback and Shield Arms' continuous improvement process:
- Updated magazine release assembly - Enhanced ergonomics and more positive engagement
- Integrated last-round bolt hold open (LRBHO) - Automatic notification when magazine is empty
- Increased parts compatibility - Works with more aftermarket AR-15 components
- Refined cosmetic details - Improved finish quality and visual appeal
- Ambidextrous trigger finger rests - Grooves above and below mag release for enhanced control
- Threaded bolt catch pin - Easier installation and maintenance
Key Features & Specifications
- Integrated Folding Mechanism - Built into the lower receiver, not an adapter, for maximum strength and minimal bulk
- Glock Magazine Compatible - Accepts all Glock double-stack 9mm magazines (G17, G19, G34, aftermarket extended mags)
- 7075-T6 Billet Construction - Aircraft-grade aluminum for exceptional strength-to-weight ratio
- Proprietary Buffer System - Shield Arms 7.0 oz stainless steel buffer with configurable steel weight for tuning
- Threaded Buffer Retaining Pin - Secure retention with easy disassembly
- Precision Magazine Well - Beveled feed lips for fast, fumble-free magazine changes
- Short-Throw Selector Compatible - Works with 45° and 60° fire control selectors
- Mil-Spec Hard Anodizing - Matte black finish per Mil 8625 Type 3 Class 2 for maximum durability
Build Considerations
This is a stripped lower receiver. You will need to source additional components to complete your build, including:
- 9mm-compatible AR-15 upper receiver assembly
- AR-15 lower parts kit (trigger, hammer, springs, pins, etc.)
- Buffer tube, castle nut, and end plate
- Pistol grip and stock or brace
- Glock-pattern 9mm magazines
Note: The SA-9 includes Shield Arms' proprietary buffer. Loctite 242 (blue) is included for proper installation of threaded components.
Made in USA with Lifetime Warranty
Every SA-9 Gen2 lower receiver is precision-machined in Shield Arms' Bigfork, Montana facility using state-of-the-art CNC equipment. We stand behind our products with a 100% lifetime warranty against manufacturing defects. When you choose Shield Arms, you're supporting American manufacturing and receiving a product backed by decades of machining expertise and firearms industry knowledge.
Technical Specifications
| Model |
SA-9 Gen2 Stripped Folding Lower Receiver |
| Caliber |
9mm Luger (9x19mm) |
| Operation |
Closed-bolt, blowback-operated |
| Magazine Compatibility |
Glock double-stack 9mm (G17, G19, G34, aftermarket) |
| Material |
7075-T6 aircraft-grade billet aluminum |
| Finish |
Matte black hard-coat anodized (Mil 8625 Type 3 Class 2) |
| Weight |
11.2 oz (stripped) |
| Buffer System |
Shield Arms proprietary 7.0 oz SS buffer with configurable weight |
| Fire Control Compatibility |
Standard AR-15 FCG, 45° and 60° short-throw selectors |
| Special Features |
Integrated folding mechanism, last-round bolt hold open, threaded pins |
| Manufacturing |
Precision CNC machined in Bigfork, Montana, USA |
| Warranty |
Lifetime |
Comparison: Folding Adapter vs. Integrated Folding Lower
| Feature |
SA-9 Gen2 Integrated |
Traditional Folding Adapter |
| Installation |
No adapter needed - built in |
Requires separate adapter purchase and installation |
| Strength |
Machined from single billet - maximum strength |
Additional hinge point creates potential weakness |
| Weight |
11.2 oz (no added adapter weight) |
Standard lower + 8-12 oz adapter |
| Profile |
Sleek, integrated design |
Bulkier with visible adapter mechanism |
| Folded Length Reduction |
~8-10 inches shorter |
~8-10 inches shorter |
| Cost |
Single purchase |
Lower + adapter (often more expensive combined) |
| Reliability |
Fewer components, fewer failure points |
Additional moving parts and pins |
Frequently Asked Questions
What magazines does the SA-9 Gen2 accept?
The SA-9 Gen2 accepts all Glock double-stack 9mm magazines (G17, G19, etc). Standard capacity magazines (15-17 rounds) and extended capacity magazines (33+ rounds) all work seamlessly.
Can I fire the SA-9 when folded?
No. Like all folding lower receivers and folding stock adapters, the SA-9 cannot and should not be fired in the folded position. The folding mechanism is designed solely for compact storage and transport. Always ensure the lower is fully unfolded and locked before loading or firing.
What upper receivers are compatible with the SA-9 Gen2?
The SA-9 Gen2 uses a standard AR-15 lower receiver interface and accepts any Mil-Spec AR-15 upper receiver chambered in 9mm. You'll need a dedicated 9mm upper with appropriate bolt and barrel. Popular options include dedicated 9mm Colt pattern uppers, though you'll be using Glock magazines with the SA-9 lower.
Does the Gen2 include a buffer and buffer spring?
Yes, the SA-9 Gen2 includes Shield Arms' proprietary 7.0 oz stainless steel buffer with configurable steel weight. You will need to provide your own buffer spring and buffer tube. The included buffer is specifically designed for 9mm blowback operation.
Is this lower receiver considered a pistol or rifle?
When sold as a stripped lower receiver, the SA-9 Gen2 is classified as "other" and is transferred as a receiver. How you build it determines its classification: installing a stock and 16"+ barrel makes it a rifle, while installing a pistol brace and shorter barrel makes it a pistol. Always ensure your build complies with federal, state, and local laws, including NFA regulations.
Will my existing AR-15 lower parts kit work with the SA-9?
Yes, the SA-9 Gen2 is designed for maximum parts compatibility and accepts standard AR-15 lower parts kits, triggers, and fire control groups. The Gen2 update specifically increased compatibility with aftermarket components. You can use your preferred trigger, safety selector (including 45° and 60° short-throw), and other standard AR components.
What is the integrated last-round bolt hold open (LRBHO)?
The Gen2 features an integrated LRBHO system that automatically locks the bolt to the rear when the last round is fired from the magazine, providing a visual and tactile indication that the magazine is empty. This is a significant improvement over Gen1 and many competing 9mm AR lowers that lack this feature.
How much shorter is the SA-9 when folded?
When folded, the SA-9 reduces the overall length of your firearm by approximately 8-10 inches, depending on your specific build configuration. This makes it significantly more compact for storage in vehicles, bags, or safes while maintaining the ability to quickly deploy to full length.
Can I use this lower for a competition PCC build?
Absolutely. The SA-9 Gen2 is an excellent foundation for competitive pistol caliber carbine builds. The Glock magazine compatibility means you can use high-capacity aftermarket mags, the LRBHO provides fast empty reloads, and the precision-machined magazine well with beveled feed lips ensures reliable, fast magazine changes under competition pressure.
What's included with the SA-9 Gen2 purchase?
The SA-9 Gen2 includes the stripped lower receiver, Shield Arms proprietary 7.0 oz stainless steel buffer, with threaded buffer retaining pin and Shield Arms magazine release assembly installed. You'll need to source a lower parts kit, buffer tube, pistol grip, stock/brace, and upper receiver assembly separately.
Does Shield Arms offer support for building my SA-9?
Yes! Shield Arms provides comprehensive installation guides and technical support. Visit our installation guides page for detailed instructions, and our customer service team is available to answer specific questions about your build. We're committed to ensuring your SA-9 build is successful.
What is the warranty on the SA-9 Gen2?
Every SA-9 Gen2 is backed by Shield Arms' 100% lifetime warranty against manufacturing defects. If you experience any issues with materials or workmanship, we'll make it right. This warranty reflects our confidence in American manufacturing and our commitment to customer satisfaction.
Who Should Buy the SA-9 Gen2?
- PCC Competitors - Build a competition-ready pistol caliber carbine with Glock magazine compatibility and integrated LRBHO for faster reloads
- Home Defense Builders - Create a compact, reliable 9mm platform that's easy to store yet quick to deploy
- Tactical Professionals - Law enforcement and security professionals who need a compact 9mm carbine that folds for vehicle storage
- Backpackers & Outdoorsmen - Hunters and outdoorsmen who want a lightweight defensive firearm that packs small
- AR-15 Enthusiasts - Builders who want something unique and innovative beyond standard AR platforms
- Range Day Shooters - Anyone looking for an affordable-to-shoot 9mm carbine for recreational use
- Multi-Gun Shooters - Competitive shooters who need magazine compatibility with their Glock pistols
- Apartment Dwellers - Gun owners with limited storage space who need compact firearm solutions
Installation & Building Your SA-9
Building an AR-15 lower receiver requires basic gunsmithing tools and mechanical aptitude. The SA-9 Gen2 installs like a standard AR-15 lower with a few unique considerations for the folding mechanism and 9mm-specific components. If you're new to AR builds, consider having a qualified gunsmith assist with your first build.
Recommended Accessories & Compatible Products
- Mountain Partisan Sling - Premium two-point sling designed for tactical applications, perfect for your SA-9 build
- Magpul PMAG Gen 2 +5 Extension - While designed for AR magazines, Shield Arms offers premium magazine extensions for other platforms
- Magpul PMAG Gen 3 +5 Extension - Extend your magazine capacity with Shield Arms' precision-machined extensions
- Glock 9mm Magazines - Stock up on factory Glock or aftermarket 9mm magazines for your SA-9 build
- AR-15 Lower Parts Kit - Complete your build with a quality LPK including trigger, hammer, pins, and springs
- Enhanced Bolt Catch - Upgrade to an extended or ambidextrous bolt catch for easier LRBHO engagement
- Premium Trigger Group - Enhance your SA-9's performance with a quality single-stage or two-stage trigger
Ready to build your ultimate 9mm folding carbine? The SA-9 Gen2 combines Shield Arms' patented folding technology with Glock magazine reliability and Gen2 improvements. Backed by our lifetime warranty and made in Montana, USA.
