Polymer80 LR-308 80% Lower Receiver - polymer 80
About this product
The Polymer80 LR-308 80% Lower Receiver is an unfinished polymer firearm lower receiver designed for hobbyist completion using standard shop tools. It is part of Polymer80's discontinued line of 80% components and is sold with a machining jig. This final production run represents the remaining inventory before the product line ends.
What is the Polymer80 LR-308 80% Lower Receiver used for?
This receiver is used for building a custom LR-308/AR-10 pattern rifle by completing the remaining 20% of the machining yourself. The primary functions are to serve as the serialized firearm component once completed and to accept standard AR-10 / LR-308 upper receivers and lower parts kits. Completion requires milling out the fire control group pocket and drilling the selector and pin holes using the included jig and a router or drill press.
How does the Polymer80 LR-308 80% Lower Receiver compare to the .308 80% Lower – Billet?
The polymer LR-308 receiver is over 60% lighter than the aluminum .308 80% Lower – Billet, weighing approximately 15 oz compared to a typical billet aluminum lower's 38 oz. The Polymer80 version is easier to machine with polymer-specific drill bits and requires less tooling force, but the billet aluminum alternative offers superior long-term dimensional stability under thermal stress and higher perceived durability. For a detailed comparison of machining polymer versus aluminum, see our technical guide on Best Drill Bits for Polymer Frame Modifications.
What does it weigh and what are the dimensions?
The unfinished polymer lower weighs 15.2 ounces. Its critical dimensions are a 1.25-inch wide magazine well and a 7.62-inch length from the rear of the buffer tube thread to the front takedown pin lug. The receiver walls have a nominal thickness of 0.187 inches in the stress-bearing areas around the buffer tower and fire control group pocket.
Who is this NOT for?
This product is not suitable for individuals unfamiliar with basic machining using a router or drill press. It is also not for builders seeking a metal receiver for heavy-duty use or those in jurisdictions where manufacturing an 80% receiver for personal use is prohibited. If you require a finished, serialized component ready for immediate assembly, consider our finished 80% Lower Fire/Safe Marked - Anodized Black.
What's in the box?
The package contains one 80% complete Polymer80 LR-308 lower receiver blank and one polymer machining jig. The jig is pre-assembled and includes all necessary drill bushings and guide holes for completing the lower receiver to 100% functional status. No tools, parts kits, or finishing supplies are included.
Is the Polymer80 LR-308 80% Lower Receiver worth it at $50.99?
At its closeout price of $50.99, it represents a significant cost savings compared to a completed serialized lower, which typically starts above $100. The value is contingent on your ability to perform the final machining correctly and your access to the required tools. For the capable hobbyist with the proper equipment, the savings offset the time investment of approximately 90-120 minutes for completion.
Specs at a glance
Video review
Pros & cons
What works
- Weighs 15.2 oz — approximately 60% lighter than standard billet aluminum LR-308 lowers
- Final sale price of $50.99 is typically half the cost of a completed serialized lower
- Includes pre-assembled polymer jig with hardened steel drill bushings
- Mills easily with standard router bits and polymer-specific drill bits in under 120 minutes
Trade-offs
- Final production run — no future warranty support or replacement parts from Polymer80
- Requires user-supplied router, drill press, and vise — adds $200+ minimum tooling cost
- Polymer construction has higher thermal expansion coefficient than aluminum — less ideal for sustained high-volume fire
- No fire/safe markings or serial number plate pre-installed
Expert review
Key attributes
| Platform | LR-308 / AR-10 |
| Completion Status | 80% lower receiver |
| Material | Polymer |
| Included Jig | Yes |
| Weight | 15.2 oz |
| Magazine Compatibility | DPMS pattern .308 magazines |
| Buffer System | .308 rifle-length |
| Condition | New, final production |
Specifications
| platform | LR-308 |
| completion_status | 80% lower receiver |
| included_jig | yes |
| manufacturer | Polymer80 |
Frequently asked questions
- Is it compatible with standard DPMS pattern LR-308 parts?
- Yes, it is designed for DPMS pattern LR-308/AR-10 components. It accepts standard DPMS pattern upper receivers, barrel nuts, and LR-308 lower parts kits from vendors like Aero Precision and Brownells. The buffer system requires a .308 rifle-length buffer tube and spring.
- Does it work with Magpul PRS Gen3 stocks?
- Yes, provided you use a compatible .308 rifle-length buffer tube. The receiver's threaded buffer extension is standard for an AR-10 platform. Ensure the stock kit includes the correct tube diameter for the PRS Gen3's clamping mechanism.
- How long does shipping take?
- Standard processing time is 3-5 business days before shipment. Once shipped, standard ground delivery within the continental U.S. typically takes 5-7 additional business days. Expedited shipping options are available at checkout for an additional fee.
- Can I return it if I damage it during milling?
- No. All sales of 80% lower receivers are final. Damage incurred during the completion process voids any potential warranty coverage. We recommend practicing your technique on scrap polymer material first. For warranty details on completed products, consult our guide on <a href="/blog/calculating-polymer-frame-warranty-coverage-limits/">Calculating Polymer Frame Warranty Coverage Limits</a>.
- Does this work with a 5.56/223 Wylde upper?
- No. The LR-308 platform is dimensionally larger than the AR-15 platform. This lower receiver is specifically sized for .308 Winchester/7.62x51mm NATO and similar cartridges (e.g., 6.5 Creedmoor) and will not mate with a 5.56 NATO upper receiver.