Polymer80 LR-308 80% Lower Receiver
- Firearms ship to the FFL dealer you choose, in any state
- Free shipping on orders over $99 · ships in 1–2 business days
- 30-day returns on unused parts and accessories
About this product
The Polymer80 LR-308 80% Lower Receiver is a raw, unfinished component designed for building a custom .308/7.62x51mm AR-10 pattern rifle using common machining tools. It is compatible with the DPMS Gen1 platform, requiring the builder to complete critical fire-control areas to create a functional firearm. This receiver starts as precision-forged 7075-T6 aluminum, offering a robust foundation for a high-pressure long-range rifle build.
What is the Polymer80 LR-308 80% Lower Receiver used for?
This 80% lower receiver serves as the foundation for building a custom, serial-number-free .308 caliber AR-10 rifle. You use a dedicated jig, like the 80% .308 Easy Jig® Gen 1, and standard workshop tools to mill out the fire control cavity, drill the selector and trigger pin holes, and finish the buffer tube threads. The completed assembly then accepts a DPMS Gen1 upper receiver, buffer system, and a .308 lower parts kit to form a legal firearm.
How does the Polymer80 LR-308 compare to the 308 80% Lower – Billet?
The Polymer80 LR-308 is forged, while the alternative 308 80% Lower – Billet is machined from a solid block of aluminum. The forged 7075-T6 receiver has superior grain structure and tensile strength, making it approximately 10-15% more resistant to flex under heavy recoil, which is critical for maintaining zero on a long-range .308 platform. The billet receiver offers more complex external machining options but at a higher base weight of 14.8 ounces versus the forged unit's 12.1 ounces.
What does it weigh and what are the dimensions?
The raw receiver blank weighs 12.1 ounces (343 grams) and measures 8.7 inches in length, 2.1 inches in width, and 1.5 inches in height at the buffer tower. The fire control pocket requires the removal of approximately 1.8 cubic inches of aluminum during milling, which takes about 25-35 minutes with a proper end mill like the 5/16" High Speed End Mill. Thread engagement for the buffer tube measures 0.85 inches deep.
Who is this NOT for?
This receiver is not suitable for first-time builders without access to a drill press, milling vise, or a dedicated 80% jig. It is also not compatible with Armalite AR-10 pattern uppers or DPMS Gen2 components—attempting a fit will result in a 0.045-inch misalignment at the takedown pin. Furthermore, it is not for builders seeking a pre-finished anodized part; this receiver ships raw or with a basic black oxide finish that requires final treatment.
What's in the box?
The box contains only the 80% lower receiver blank. It does not include a jig, tooling, parts kit, or finishing supplies. This aligns with our methodical approach: you select the jig for your specific tools, the drill bits for your material, and the parts kit for your intended use, preventing tolerance stacking from mismatched component lots.
Is the Polymer80 LR-308 worth it at $50.99?
At $50.99, the Polymer80 LR-308 represents a measurable cost advantage for experienced builders prioritizing material integrity over external finish. A comparable finished DPMS Gen1 lower typically costs $95-$130. The savings of roughly $45-$80 directly funds higher-quality components, like a better trigger or barrel. The investment only makes sense if you already own or budget for the required $180-$250 in jigs and tooling; otherwise, a complete lower is the efficient choice.