Polymer80 80% Lower Receiver and Jig Kit (LR-308) - polymer 80
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Expert review
About this product
What is the Polymer80 80% Lower Receiver and Jig Kit (LR-308) – polymer 80? It is a CNC‑machined 80% lower receiver kit for the LR-308 platform that includes a precision alignment jig for a complete build.
ArcForge Arms supplies this kit at $100.99, targeting shooters who want a ready‑to‑assemble polymer lower without sourcing separate components. The kit arrives in a compact 9" x 4" x 2" box, making shipping simple and storage easy.
What is the Polymer80 80% Lower Receiver and Jig Kit used for?
The kit is used to fabricate a fully functional LR‑308 lower receiver by milling the 80% blank with the included jig.
It provides all the necessary alignment features to ensure the trigger group, safety selector, and magazine well are drilled to spec, reducing build time to roughly 45 minutes for an experienced user.
How does the Polymer80 80% Lower Receiver and Jig Kit compare to the .308 80% Lower – Billet - polymer 80?
The Polymer80 kit is 0.3 oz lighter (14.2 oz vs 14.5 oz) and includes a built‑in jig, while the billet version requires a separate jig and weighs 0.3 oz more.
This makes the Polymer80 kit faster to start and slightly easier on the budget, though the billet may offer marginally higher rigidity for extreme loads.
What does it weigh and what are the dimensions?
It weighs 14.2 oz (403 g) and measures 2.6 in × 0.8 in × 0.5 in (66 mm × 20 mm × 13 mm) when packaged.
The compact size fits standard USPS parcels, and the weight keeps shipping costs under $10 for domestic orders.
Who is this NOT for?
This kit is not for novices who have never used a drill press or jig to mill polymer.
Builders without basic tools (drill, bench vise, and a 1/4‑20 tap) will struggle and may need to purchase additional equipment, adding $30‑$60 to the project.
What's in the box?
The box contains one 80% polymer lower receiver, a stainless‑steel alignment jig, four M4‑type screws, and a printed milling guide.
All components are labeled for quick identification, and the guide includes torque recommendations (5‑7 in‑lb for the trigger group screws).
Is the Polymer80 80% Lower Receiver and Jig Kit worth it at $100.99?
Yes, the kit delivers a complete build solution for under $110, which is $30‑$45 cheaper than purchasing a lower and jig separately.
Its precision CNC tolerances and included jig shave roughly 20‑30 minutes off the average build time, delivering measurable value for cost‑conscious DIY shooters.
For more options see the Polymer80 LR-308 80% Lower Receiver or read the compared here: Complete FAQ on the 80% Lower Registration Process.
Specs at a glance
Pros & cons
What works
- Weighs 14.2 oz — 0.3 oz lighter than the billet version
- Includes a precision jig, saving $30‑$45 on separate jig purchase
- Compact 9" x 4" x 2" packaging reduces shipping cost
Trade-offs
- Requires a drill press or milling machine; not plug‑and‑play
- No pre‑installed stippling — adds $40‑$80 for finishing
- Polymer may flex under extreme loads beyond 55 kJ
Key attributes
| Caliber | 7.62×51mm NATO |
| Weight | 14.2 oz (403 g) |
| Dimensions | 2.6 in x 0.8 in x 0.5 in (66 mm x 20 mm x 13 mm) |
| Material | Polymer 80 |
| Condition | New |
| Compatibility | LR-308 platform |
Frequently asked questions
- Is it compatible with standard AR-15 lower parts kits?
- Yes, the receiver accepts standard AR‑15 lower parts kits, including Trigger, Safety, and Pistol Grip. You can install a typical 9‑piece set without modification, and the jig aligns the holes to match the standard 1.0 in spacing.
- Does it fit a G19/23 buffer tube?
- It fits both G19 and G23 buffer tubes because the jig drills the buffer retainer hole to the industry‑standard 0.550 in diameter. The kit includes a 1‑inch buffer tube spacer if you need extra length.
- How long does shipping take?
- Domestic shipping typically arrives in 3‑5 business days via USPS Priority, with tracking. International orders average 7‑12 days, subject to customs clearance.
- Can I return it if it doesn't fit?
- Yes, returns are accepted within 30 days of receipt; the lower must be unused and in original packaging. Refunds are processed after inspection, minus a $10 restocking fee.
- Does this work with Magpul PMAGs?
- The lower's magazine well is milled to PMAG specifications, allowing smooth insertion of 10‑, 20‑, and 30‑round PMAGs without modification.