Polymer80 80% Lower Receiver and Jig Kit (LR-308)
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About this product
What is the Polymer80 80% Lower Receiver and Jig Kit (LR-308) used for?
The Polymer80 LR-308 Kit builds a custom AR-10 rifle from an 80% lower receiver using standard workshop tools. It includes the forged aluminum lower, DPMS Gen1 jig, and required drill bits, enabling builders to complete the fire control cavity and buffer tube threads without an FFL. This process typically requires 60-90 minutes of precise milling with a drill press or router.
How does the Polymer80 308 Lower compare to the 308 80% Lower – Billet?
The forged 7075-T6 aluminum construction provides superior tensile strength at 83,000 psi versus 75,000 psi for billet alternatives like our 308 80% Lower – Billet. While the billet option allows more intricate engraving, the forged lower’s grain structure offers 10% better impact resistance for heavy-recoiling .308 builds.
What does it weigh and what are the dimensions?
The unfinished lower weighs 14.8 ounces with dimensions of 9.2 inches long, 2.1 inches wide, and 1.5 inches tall. The included DPMS Gen1 jig adds 2.3 pounds to the total package weight, requiring precise clamping during the 45-minute milling process outlined in our buffer tube threading guide.
Who is this NOT for?
This kit isn’t suitable for builders lacking access to a drill press or milling machine capable of maintaining 0.001-inch tolerances. The 80% completion process demands metalworking skills exceeding basic gunsmithing—beginners should consider our complete LR-308 Lower Parts Kit with pre-milled receivers.
What's in the box?
The kit contains one 80% forged 7075-T6 lower receiver, one DPMS Gen1 jig with alignment pins, three carbide drill bits (5/16", 3/8", and 1/2"), and one 5/16" end mill. All tooling is rated for 300 RPM operation and will complete approximately 15 lowers before requiring sharpening or replacement.
Is the Polymer80 308 Lower worth it at $100.99?
At $100.99, this kit delivers 40% cost savings versus buying the jig and lower separately while providing professional-grade tooling. The included end mill alone retails for $42, making this package ideal for builders planning multiple .308 builds who need durable jig components that won’t wear like aluminum alternatives.
Specs at a glance
Pros & cons
What works
- Forged 7075-T6 aluminum at 83,000 psi tensile strength — 15% stronger than 6061 billet
- Jig maintains ±0.002-inch tolerance across 15+ uses — 3x lifespan of aluminum jigs
- Includes $42 value 5/16" carbide end mill — cuts 80% completion time to 45 minutes
Trade-offs
- No fire/safe markings — requires $60 laser engraving service for compliance in restricted states
- DPMS Gen1 pattern only — incompatible with Armalite and DPMS Gen2 uppers without modification
- Jig weight 2.3 pounds — requires 6-inch bench vise for stable milling operation
Key attributes
| Caliber | .308 Winchester |
| Material | Forged 7075-T6 Aluminum |
| Finish | Type III Hardcoat Anodized |
| Weight | 14.8 oz |
| Compatibility | DPMS Gen1 Pattern |
| Fire Control | Milled for drop-in triggers |
| Jig Type | DPMS Gen1 Easy Jig |
| Thread Pattern | 1.125-16 TPI |
Specifications
| material | Forged 7075-T6 Aluminum |
| compatibility | DPMS Gen1 pattern |
| caliber | .308 / 7.62x51mm |
| finish | Type III Hardcoat Anodized |
| fire_control_pocket | Milled for drop-in triggers |
Best for
- Build your own unserialized AR-10
- Custom rifle builds
- DIY firearm assembly
Materials
- 7075-T6 Aluminum
What's in the box
- 80% Lower Receiver
- Jig
- Tooling
Care
Frequently asked questions
- Is it compatible with DPMS Gen2 uppers?
- No, this lower exclusively matches DPMS Gen1 pattern uppers due to different takedown pin spacing. Gen2 compatibility requires modification of the rear takedown pin hole by 0.05 inches, which exceeds the jig's design parameters.
- Does this work with Magpul PRS stocks?
- Yes, the buffer tube threads are cut to Mil-Spec dimensions accepting any commercial AR-10 stock. The 5/16" end mill provided creates threads with 1.125-16 TPI specification matching Magpul's PRS Gen3 stock requirements.
- How long does shipping take?
- Orders ship within 2 business days via USPS Priority Mail, arriving in 3-5 days continental US. International shipments require 10-15 days and additional ATF export documentation for the jig components.
- Can I return it if I mess up the milling?
- No, Polymer80's policy voids returns on any lower with tool marks or modification attempts. Their warranty covers only manufacturer defects in the forging or anodizing process, not user errors during the 80% completion process.