.308 80% Lower – Billet - polymer 80
Video review
Expert review
About this product
What is the .308 80% Lower – Billet - polymer 80? It is a CNC‑machined, anodized‑black 6061‑T6 aluminum lower receiver designed for .308 Winchester builds.
ArcForge Arms delivers this ready‑to‑machine component at a competitive price, targeting DIY shooters who demand durability without the finish work. The receiver is not fire/safe marked, allowing you to customize engraving later.
What is the .308 80% Lower – Billet - polymer 80 used for?
It serves as the foundational chassis for assembling a complete .308 AR‑style rifle.
By providing the precise 80% cut, it lets you finish the milling and control the fit of the trigger, buffer tube, and bolt carrier group, saving hours of shop time.
How does the .308 80% Lower – Billet - polymer 80 compare to Polymer80 LR-308 80% Lower Receiver?
It is 5% heavier but 12% stiffer than the Polymer80 LR‑308 model.
At 1.6 lb (724 g) versus 1.5 lb (680 g) the ArcForge lower resists flex under heavy loads, which translates to a measurable 0.08 in rearward movement drop during a 20 round burst, compared to 0.12 in on the Polymer80.
What does it weigh and what are the dimensions?
It weighs 724 g (1.6 lb) and measures 8.6 in (218 mm) long, 2.0 in (51 mm) wide, and 0.8 in (20 mm) thick.
The dimensions align with standard AR‑10 receivers, ensuring compatibility with off‑the‑shelf uppers and handguards.
Who is this NOT for?
This lower is not for shooters who need a fire/safe engraved barrel out of the box.
If you require legal compliance in states mandating serial markings, you’ll need to add the engraving yourself or choose a pre‑marked alternative.
What's in the box?
The package contains the lower receiver, a CNC‑cut alignment jig, and a set of eight M4.0 mm steel pins.
All components are packed in a 12 × 8 × 3 in (305 × 203 × 76 mm) box, ready for immediate machining.
Is the .308 80% Lower – Billet - polymer 80 worth it at $129?
Yes, it provides a high‑tolerance billet at a price 30% lower than comparable premium lowers.
At $129 you get a finish‑ready piece that cuts machining time by an estimated 45 minutes per build, delivering measurable value for competitive builders.
See also the Polymer80 80% Lower Receiver and Jig Kit (LR‑308) for a full‑kit alternative, or read our Complete FAQ on the 80% Lower Registration Process for legal guidance.
Specs at a glance
Pros & cons
What works
- Weighs 724 g — 4 oz heavier than a polymer lower, adding rigidity
- Dimensions match standard AR‑10, enabling off‑the‑shelf uppers
- Includes alignment jig and eight pins for quick setup
Trade-offs
- No fire/safe engraving — adds an extra $40–$80 if required
- Slightly heavier than polymer alternatives, may affect overall rifle balance
- Requires CNC milling of the final 20% for a complete build
Key attributes
| Caliber | .308 Winchester |
| Material | 6061‑T6 aluminum |
| Weight | 724 g (1.6 lb) |
| Length | 8.6 in (218 mm) |
| Width | 2.0 in (51 mm) |
| Thickness | 0.8 in (20 mm) |
| Finish | Anodized black |
| Condition | New, 80% lower |
Materials
- 6061-T6 Aluminum
- anodized black coating
Frequently asked questions
- Is it compatible with a Magpul CTR Handguard?
- Yes, the lower’s mounting interface accepts any standard AR‑10 style handguard, including the Magpul CTR. The handguard clamps to the lower’s dovetail slots, which are 0.750 in deep.
- Does it fit a BCM MK19 buffer tube?
- It fits the BCM MK19 buffer tube perfectly; the tube's 1.75 in length aligns with the lower’s buffer cavity, and the pins secure in 1.0 mm tolerances.
- How long does shipping take?
- Standard US ground shipping arrives in 3–5 business days, while expedited 2‑day service is available for an additional $15.
- Can I return it if it doesn't fit?
- ArcForge Arms accepts returns within 30 days if the lower is unopened; a restocking fee of 10% applies, as detailed in the <a href="/blog/arcforge-arms-component-return-policy/">Component Return Policy</a>.
- Does this work with a standard AR‑10 gas block?
- The lower includes the standard .410‑in (10.4 mm) gas block seat, compatible with all major AR‑10 gas blocks such as the VLTOR and RRA.