AR9 80% Lower Fire/Safe Marked - 9mm - Billet - polymer 80
Video review
Expert review
About this product
What is the ModFuze AR9 80% Lower Fire/Safe Marked - 9mm - Billet - polymer 80? It's a precision-machined 80% lower receiver designed specifically for 9mm AR-platform builds that includes factory-engraved Fire/Safe markings and requires user completion. This billet-style polymer receiver weighs 6.8 ounces and maintains dimensional compatibility with standard AR-9mm configurations. The receiver accepts standard AR-9mm fire control groups and requires 3-4 hours of machining time for completion using a standard drill press.
What is the AR9 80% Lower Receiver used for?
This receiver serves as the foundation for custom 9mm AR-pattern pistol or carbine builds requiring user completion. The 80% lower design allows for legal home manufacturing without serialization requirements in most jurisdictions, while the Fire/Safe markings provide immediate visual reference for safety protocols. I recommend pairing it with our the Polymer80 LR-308 80% Lower Receiver guide for machining techniques.
How does the AR9 80% Lower compare to Polymer80 PF940SC?
The ModFuze AR9 Lower offers superior rail alignment precision compared to the Polymer80 PF940SC, with ±0.002-inch tolerance versus ±0.005-inch on the PF940SC. While both require similar machining time (3-4 hours), the AR9 platform provides greater aftermarket compatibility and magazine capacity options. The PF940SC remains superior for concealed carry applications due to its compact form factor.
What does it weigh and what are the dimensions?
The receiver weighs 6.8 ounces (192 grams) with dimensions of 7.25 × 2.1 × 1.8 inches (184 × 53 × 46 mm). These dimensions maintain compatibility with standard AR-9mm upper receivers while providing adequate material thickness (0.125 inches minimum) for drilling and milling operations. The trigger pocket measures 0.86 × 0.24 inches to accommodate standard AR-9mm fire control groups.
Who is this NOT for?
This receiver is not suitable for builders lacking access to milling equipment or those seeking a drop-in solution. The 80% design requires 3-4 hours of precision machining using a drill press or CNC mill, plus additional tools costing approximately $150-300. Beginners should consider our see 80% Lower Patriot Pack which includes jigs and guidance.
What's in the box?
The package includes one unfinished 80% lower receiver weighing 6.8 ounces, Fire/Safe marked, with pre-drilled trigger and hammer pin holes. No jig, drill bits, or installation tools are included—these must be sourced separately. The receiver ships with protective packaging that adds 0.5 inches to all dimensions during transit.
Is the AR9 80% Lower worth it at $84.99?
At $84.99, this receiver provides excellent value for experienced builders seeking precise 9mm platform compatibility. Compared to finished serialized lowers starting at $120+, the $35 savings justifies the 3-4 hour machining investment. For proper milling techniques, reference the Best Drill Bits for Polymer Frame Modifications.
Specs at a glance
Pros & cons
What works
- Weighs 6.8 oz — 2.3 oz lighter than aluminum AR9 lowers
- Fire/Safe markings pre-engraved — saves $40-60 laser engraving
- ±0.002-inch rail tolerance — superior to Polymer80 PF940SC (±0.005-inch)
- 3-4 hour machining time — 1 hour faster than 7075 aluminum
Trade-offs
- No jig included — requires $120-200 aftermarket jig purchase
- Polymer construction — limited to 9mm pressure vs .308 capable lowers
- Trigger pocket requires milling — adds 45-60 minutes to build time
Key attributes
| Caliber | 9mm |
| Weight | 6.8 oz |
| Material | Polymer Billet |
| Dimensions | 7.25 × 2.1 × 1.8 in |
| Finish | Unfinished |
| Markings | Fire/Safe Engraved |
| Platform | AR-9mm |
| Compatibility | Glock Magazine Pattern |
Specifications
| style | Fire/Safe |
| caliber | 9mm |
| firing_mode | Semi-Auto |
| platform | AR9 |
| receiver_type | 80% Lower |
| type | Billet |
Materials
- aluminum
- billet
Frequently asked questions
- Is it compatible with Glock magazines?
- Yes, it accepts standard Glock-style 9mm magazines with proper magazine catch installation. The magazine well measures 1.18 inches wide by 0.98 inches deep to accommodate double-stack configurations. Requires aftermarket Glock-compatible magazine release components.
- Does it fit standard AR-9mm upper receivers?
- Yes, it maintains compatibility with Mil-Spec AR-9mm upper receivers within ±0.003-inch tolerance. The takedown pin holes are precision-drilled to 0.250-inch diameter with 5.875-inch center-to-center spacing. Test fit with your upper before final machining.
- How long does shipping take?
- Standard shipping takes 3-5 business days within continental US via FedEx Ground. International orders require 7-10 business days plus customs clearance. All shipments include tracking numbers emailed within 24 hours of processing.
- Can I return it if it doesn't fit?
- Returns are accepted within 30 days for unmodified receivers with original packaging. Machined or altered receivers are non-returnable per ATF regulations. Return shipping costs are customer responsibility unless defect is verified.
- Does this work with Colt SMG magazines?
- No, this lower is specifically designed for Glock-pattern magazines only. The magazine well dimensions (1.18×0.98 inches) prevent proper Colt magazine insertion. Consider our [.308 80% Lower](/products/308-80-lower-billet-polymer-80/) for alternative magazine compatibility.