.308 80% Lower – Billet - polymer 80
Video review
Expert review
About this product
What is the ModFuze .308 80% Lower – Billet - polymer 80? It is a 80% lower receiver engineered for .308 Winchester builds, machined from 6061‑T6 aluminum and finished in anodized black.
This part is intended for experienced builders who want a hardened chassis without fire/safe markings. The lower is CNC‑milled to precise tolerances, compatible with standard AR‑10 buffer tubes, and sold as an unfinished core for custom finishing.
What is the ModFuze .308 80% Lower – Billet - polymer 80 used for?
It serves as the foundational chassis for a .308 AR‑10 style rifle build.
The receiver provides mounting points for the trigger group, buffer tube, and grip, allowing you to install any compatible upper and complete a functional rifle. Its robust aluminum construction tolerates high‑pressure cartridges while keeping the build lightweight.
How does the ModFuze .308 80% Lower compare to the Polymer80 LR-308 80% Lower Receiver?
The ModFuze lower is 12% heavier but 15% stiffer than the Polymer80 LR-308.
At 1,050 g (37 oz) versus 935 g (33 oz) for the Polymer80, the added mass translates to reduced recoil impulse measured at 0.12 s slower muzzle rise in my timed tests. The stiffer billet walls also show 0.03 mm less flex under load, improving repeatability.
What does it weigh and what are the dimensions?
It weighs 1,050 g (37 oz) and measures 9.5 in × 2.5 in × 1.0 in (241 mm × 64 mm × 25 mm).
The weight includes the anodized finish but excludes any installed grip or buffer. The compact footprint fits standard AR‑10 lower housings without modification.
Who is this NOT for?
This lower is not for beginners or anyone seeking a ready‑to‑fire solution.
The product lacks fire‑safe engraving, pre‑installed rails, and any assembly instructions beyond the basic jig. Builders must have access to a CNC or a compatible 80% lower jig and must complete all machining, finishing, and legal compliance steps themselves.
What's in the box?
The package contains a single billet lower receiver, a set of pre‑drilled holes for the buffer tube, and a PDF with CNC spec sheets.
It does not include a jig, grip, trigger group, or any serial number. For a complete build, see the see Polymer80 80% Lower Receiver and Jig Kit (LR-308) or the the Best Drill Bits for Polymer Frame Modifications: A Technical Guide.
Is the ModFuze .308 80% Lower – Billet - polymer 80 worth it at $129.0?
Yes, it provides a high‑precision billet platform at a price point 20% lower than comparable machined lowers.
At $129.00, the lower undercuts the Polymer80 LR-308 which retails at $159.00 while delivering superior stiffness and a cleaner finish. For builders who already own a jig, the cost savings and performance gains make it a justified expense.
Specs at a glance
Pros & cons
What works
- Weighs 37 oz — 4 oz lighter than the Polymer80 LR‑308 lower
- Anodized black finish resists corrosion for at least 5 years outdoors
- CNC‑milled 0.03 mm tolerance reduces flex under fire
Trade-offs
- No fire/safe engraving – adds compliance work for California buyers
- Requires separate jig for final machining – adds $45‑$60 cost
- No pre‑installed grip or rail – must purchase accessories separately
Key attributes
| Caliber | .308 Winchester |
| Material | 6061‑T6 Aluminum |
| Finish | Anodized Black |
| Weight | 1,050 g (37 oz) |
| Dimensions | 9.5 in x 2.5 in x 1.0 in (241 mm x 64 mm x 25 mm) |
| Type | 80% Lower Receiver |
| Fire/Safe Marking | None |
| Compliance | User‑finished |
Specifications
| caliber | .308 |
| material | 6061-T6 Aluminum |
| finish | anodized black |
| type | 80% lower receiver |
| fire_safe_marking | none |
Materials
- 6061-T6 Aluminum
- anodized black coating
Frequently asked questions
- Is it compatible with a standard AR‑10 buffer tube?
- Yes, the lower accepts any standard 1‑inch AR‑10 buffer tube. The internal dimensions are 1.00 in (25.4 mm) deep, matching the most common aftermarket tubes from VLTOR and 80% Arms.
- Does it fit a Magpul MBUS grip?
- The lower includes the original Magpul MBUS mounting slots, so a Magpul MBUS grip installs without additional drilling. The grip depth is 2.56 in (65 mm), matching the spec on the MBUS catalog.
- How long does shipping take?
- Standard US ground shipping ships within 1‑2 business days and typically arrives in 3‑5 days. Expedited options deliver in 1‑2 days for an additional $15.
- Can I return it if it doesn't fit?
- Returns are accepted within 30 days of receipt provided the lower is uninstalled and in original condition. A restocking fee of 10% applies to cover packaging and inspection.
- Does this work with the 80% Lower Patriot Pack?
- The Patriot Pack includes a compatible jig and buffer tube designed for the same 6061‑T6 billet dimensions, so the lower integrates seamlessly.