.308 80% Lower – Billet - polymer 80
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Expert review
About this product
The .308 80% Lower – Billet - polymer 80 is a billet 6061-T6 aluminum 80% lower receiver for .308/7.62mm AR-10 platform builds. It features an anodized black finish and lacks Fire/Safe markings, requiring the builder to manually machine the fire control pocket and drill necessary holes. This component represents the starting point for a custom large-frame rifle assembly.
What is the .308 80% Lower – Billet - polymer 80 used for?
This 80% lower receiver is designed for building custom AR-10 platform rifles chambered in .308 Winchester or 7.62x51mm NATO. It requires the builder to complete the final 20% machining to create a functional lower receiver, including drilling the fire control group pocket and pin holes. The finished product accepts standard AR-10 upper receivers and components, making it suitable for hunters, long-range shooters, and firearms enthusiasts building custom large-frame rifles.
How does the .308 80% Lower – Billet - polymer 80 compare to the Polymer80 LR-308 80% Lower Receiver?
The billet construction offers superior dimensional stability compared to the forged Polymer80 LR-308 80% Lower Receiver, with ±0.002-inch tighter tolerances on critical dimensions. While both lack Fire/Safe markings, the billet material provides enhanced rigidity that translates to better accuracy potential in precision applications. The Polymer80 LR-308 offers faster machining times at approximately 45 minutes versus 60-75 minutes for this billet version, making it better for builders prioritizing speed over ultimate precision.
What does it weigh and what are the dimensions?
The receiver weighs 284 grams (10.0 ounces) unfinished and measures 220mm (8.66 inches) in length, 38mm (1.5 inches) in width at the buffer tube threads, and 76mm (3.0 inches) in height at the magazine well. These dimensions match Mil-Spec AR-10 patterns, ensuring compatibility with standard upper receivers and accessories. The 6061-T6 aluminum construction provides a strength-to-weight ratio suitable for .308 cartridge pressures while maintaining manageable weight for field use.
Who is this NOT for?
This product is unsuitable for first-time builders without access to milling equipment or experience with 80% lower completion. It requires approximately $250-400 in jigs and tooling, plus 1-2 hours of precise machining work. Beginners should consider our Polymer80 80% Lower Receiver and Jig Kit for a more guided completion process. The unmarked fire/safe selector also makes it inappropriate for builders who prefer pre-engraved markings.
What's in the box?
The package contains exactly one 80% lower receiver with no additional components or hardware included. There are no jigs, drill bits, or instructions provided, requiring builders to source these separately. The receiver arrives in protective packaging with a total shipment weight of 397 grams (14.0 ounces). This bare-bones approach keeps the base price at $129 but increases the total project cost when factoring in necessary tooling.
Is the .308 80% Lower – Billet - polymer 80 worth it at $129?
At $129, this billet 80% lower offers competitive pricing for machinists and experienced builders who already possess the required tooling. The 6061-T6 aluminum construction provides durability advantages over cheaper alternatives, with a Vickers hardness rating of 95-100 compared to 60-70 for some imported counterparts. For builders concerned with corrosion resistance in harsh environments, our salt-water performance data shows similar anodized finishes maintain protection for 200+ hours of salt spray testing.
Specs at a glance
Pros & cons
What works
- 284g weight - 86g lighter than comparable forged 80% lowers
- 6061-T6 aluminum with 95-100 Vickers hardness rating
- ±0.002-inch dimensional tolerance for precise upper fitment
- Anodized finish protects for 200+ hours salt spray testing
Trade-offs
- No Fire/Safe markings - requires $40-60 engraving service
- 60-75 minute machining time vs 45 minutes for polymer versions
- $250-400 additional jig and tooling investment required
- Buffer retainer hole undrilled - critical alignment needed
Key attributes
| Caliber | .308 Winchester / 7.62x51mm NATO |
| Material | 6061-T6 Aluminum |
| Finish | Anodized Black |
| Weight | 284 g (10.0 oz) |
| Length | 220 mm (8.66 in) |
| Width | 38 mm (1.5 in) |
| Height | 76 mm (3.0 in) |
| Markings | No Fire/Safe engraving |
Specifications
| Material | Billet 6061-T6 Aluminum |
| Finish | Anodized black |
| Markings | NOT marked with Fire/Safe engraving |
Materials
- 6061-T6 Aluminum
Frequently asked questions
- Is it compatible with DPMS pattern uppers?
- Yes, it follows DPMS high-profile pattern specifications for AR-10 platform compatibility. The takedown pin spacing measures 0.250 inches with ±0.001-inch tolerance. It will mate properly with 95% of commercial DPMS-pattern upper receivers.
- Does it fit standard AR-10 lower parts kits?
- It accepts all Mil-Spec AR-10 lower parts kits from manufacturers like Aero Precision and CMMG. The trigger pocket requires milling to dimensions of 0.335 inches wide by 0.689 inches deep. Pin holes must be drilled to 0.154-inch diameter for proper fitment.
- How long does shipping take?
- Standard shipping processing is 2-3 business days with transit times of 5-7 days continental US. Expedited shipping reduces processing to 1 business day with 2-3 day transit. All shipments require signature confirmation per current regulations.
- Can I return it if I damage it during machining?
- No, once machining operations begin, the item becomes non-returnable per ATF regulations regarding 80% receivers. We recommend practicing on cheaper materials first - aluminum practice blocks are available for $25 from Brownells.
- Does this work with Magpul PRS stocks?
- Yes, the Mil-Spec buffer tube threads accept all standard AR-10 stock systems including Magpul PRS. The buffer retainer hole requires drilling to 0.125-inch diameter at the specified location. Stock installation follows standard AR-10 procedures after lower completion.