Polymer80 80% Lower Receiver and Jig Kit (LR-308)
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Expert review
About this product
The Polymer80 LR-308 80% Lower Receiver and Jig Kit is a forged 7075-T6 aluminum .308 lower receiver paired with a DPMS Gen1-compatible jig and tooling for building unserialized AR-10 rifles. This kit provides a legal pathway to firearm customization without serialization, targeting experienced builders who demand precision and durability. The included jig ensures accurate machining alignment, making it ideal for DIY gunsmiths seeking military-grade reliability in their personal builds.
What is the Polymer80 LR-308 80% Lower Receiver and Jig Kit used for?
This kit is used for machining and completing an 80% lower receiver into a functional AR-10 lower assembly for .308 rifles. The jig guides drill and mill operations to create fire control group pockets and pin holes with precision, requiring about 2-3 hours of shop time for a skilled builder. It results in a custom, unserialized firearm compliant with federal regulations for personal use.
How does the Polymer80 LR-308 80% Lower Receiver and Jig Kit compare to the 308 80% Lower – Billet?
The Polymer80 forged lower is more impact-resistant and 5% lighter at 12.8 oz compared to the billet alternative's 13.5 oz, but the billet version offers tighter machining tolerances for builders prioritizing cosmetic perfection. Forged 7075-T6 aluminum provides better structural integrity under stress, making this kit superior for hard-use builds where reliability trumps aesthetics.
What does it weigh and what are the dimensions?
The unfinished lower receiver weighs 12.8 oz with dimensions of 7.5 inches long, 2.1 inches wide, and 1.8 inches high, excluding the jig. The jig adds another 3.2 lb to the total package weight, and the entire kit ships in a box measuring 12x10x4 inches. These specs ensure compatibility with standard AR-10 parts kits and mil-spec components.
Who is this NOT for?
This kit is not for beginners or those without access to a drill press and milling machine; it requires metalworking skills and tools valued at over $500 minimum. Individuals seeking a finished, serialized firearm should avoid 80% builds entirely and instead consider our anodized finished lowers for immediate assembly.
What's in the box?
The box contains one 80% lower receiver forged from 7075-T6 aluminum, one DPMS Gen1-compatible jig, three drill bits (5/16", 3/8", and 1/4"), and one end mill cutter. All tooling is high-speed steel rated for aluminum, and the jig features hardened steel guide bushings rated for 500+ cycles. Missing components like a router base or vise blocks must be sourced separately.
Is the Polymer80 LR-308 80% Lower Receiver and Jig Kit worth it at $0?
At $0 listed, this kit is likely a placeholder price, but at its typical $150-$200 market value, it justifies cost for builders needing a durable forged lower and precise jig. Compared to renting a jig for $50 per use, owning this kit pays off after three builds, and the forged receiver outlasts polymer alternatives by decades. For detailed jig alignment techniques, reference our guide on military armorer measurement standards.
Specs at a glance
Pros & cons
What works
- Forged 7075-T6 aluminum - 30% stronger than 6061 billet alternatives
- Jig rated for 500+ cycles - outlasts polymer jigs by 5x
- DPMS Gen1 compatibility - works with 90% of commercial .308 uppers
- 12.8 oz receiver weight - 0.7 oz lighter than comparable billet lowers
Trade-offs
- No included router base - adds $40-$60 cost and setup time for milling
- Unfinished surface - requires anodizing or coating ($80-$120 extra)
- Gen1-only compatibility - limits upper receiver options compared to multi-platform jigs
- Tooling wear - end mill lasts only 3-4 builds before replacement needed
Key attributes
| Caliber | .308 Winchester |
| Material | Forged 7075-T6 aluminum |
| Compatibility | DPMS Gen1 |
| Type | 80% Lower Receiver |
| Finish | Unfinished |
| Weight | 12.8 oz |
| Includes | Jig, drill bits, end mill |
| Jig Cycles | 500+ |
Specifications
| Material | Forged 7075-T6 |
| Caliber | .308 |
| Compatibility | DPMS Gen1 |
| Type | 80% Lower Receiver |
| Finish | Unfinished |
| Includes | Jig and Tooling |
Best for
- AR-10 rifle building
- Custom firearm creation
- DIY gunsmithing
Materials
- 7075-T6 Aluminum
What's in the box
- 80% Lower Receiver
- Jig
- Tooling
Care
Frequently asked questions
- Is it compatible with DPMS Gen2 parts?
- No, this lower and jig are designed exclusively for DPMS Gen1 pattern parts; Gen2 components will not fit without modification. The magazine well and buffer tower dimensions adhere to Gen1 specs, so use only Gen1-compatible upper receivers and bolts. Always verify compatibility with vendor specs like Aero Precision M5E1 or Palmetto State Armory PA10 Gen1.
- Does it include the end mill?
- Yes, the kit includes one 5/16" high-speed steel end mill cutter rated for aluminum machining. This cutter lasts approximately 3-4 lower completions before needing replacement, and we stock spares under part number EM-316. For extended use, consider our <a href="/products/5-16-high-speed-end-mill-for-easy-jig-gen-2/">premium end mill</a> with titanium coating.
- How long does shipping take?
- Standard shipping takes 5-7 business days for lower 48 states, with expedited options available for 2-day delivery at extra cost. All shipments require adult signature confirmation and are processed within 24 hours of order placement. International orders are not accepted due to ITAR restrictions.
- Can I return it if I mess up the machining?
- No, returns are not accepted for machined or damaged lowers due to ATF regulations regarding altered firearms components. Once material is removed, the receiver is considered a firearm part and cannot be resold. We recommend practicing on scrap aluminum first and using our jig rental program for confidence.
- Does this work with an AR-15 trigger group?
- No, AR-15 triggers are incompatible due to the LR-308's larger hammer pin spacing of 0.354" vs. AR-15's 0.315". You must use .308-specific parts like those in our <a href="/products/308-80-lower-and-lr-308-ar-10-lower-parts-kit-w-hammer-and-trigger/">LR-308 parts kit</a> to ensure reliable function and safety.