308 80% Lower – Billet
Video review
Expert review
About this product
The FrameSmith 308 80% Lower Billet is an unfinished DPMS-pattern AR-10 lower receiver requiring final machining of the fire control pocket and trigger pin holes. Crafted from 7075 T6 aluminum, it maintains material integrity superior to cast alternatives while demanding precise tooling. This component ships unfinished with no FFL requirement, targeting builders comfortable with mill operations exceeding simple drilling.
What is the 308 80% Lower Billet used for?
This billet serves as the foundation for custom AR-10 rifles chambered in .308 Winchester or 7.62x51mm. It accepts standard DPMS-pattern parts kits, requiring completion of the fire control pocket and drilling of three pin holes (hammer, trigger, and selector) to functional status. Builders must supply their own jig system, like the 80% .308 Easy Jig® Gen 1, to guide machining operations within ±0.005 inch tolerances.
How does the 308 80% Lower Billet compare to a forged 80% lower?
The FrameSmith billet offers thicker wall sections than typical forged 80% lowers, adding approximately 3.5 ounces of material around critical stress points. This provides superior rigidity for heavy-barrel builds but requires 15-20% more milling time to complete the fire control pocket. Forged lowers like the Aero Precision M5 80% weigh less and machine faster, but the FrameSmith billet proves better for sustained fire applications exceeding 90 rounds consecutively.
What does it weigh and what are the dimensions?
The raw billet weighs 14.8 ounces with overall dimensions of 9.75 inches long by 2.1 inches wide. The buffer tube thread depth measures 1.125 inches, requiring verification with proper thread gauging techniques before assembly. Total milling removal volume averages 1.8 cubic inches when using a 5/16" end mill.
Who is this NOT for?
This lower is unsuitable for first-time builders lacking access to a bench vise and milling machine. The 7075 T6 aluminum requires carbide tooling and flood coolant to prevent work hardening during the 45-60 minute machining process. Builders seeking a drop-in solution should consider completed lowers requiring FFL transfer instead.
What's in the box?
The package contains exactly one unfinished 308 80% lower receiver with protective foam packaging. No jig, drill bits, or lower parts kit are included—purchasers must source these separately. The raw aluminum surface arrives with light machining oil applied to prevent oxidation during shipping.
Is the 308 80% Lower Billet worth it at $129?
At this price point, the billet justifies its cost for builders requiring extreme durability beyond forged receivers. The additional $40 over basic forged 80% lowers buys measurable material redundancy in high-stress areas like the buffer tower. For precision .308 builds where receiver flex impacts accuracy beyond 600 yards, this investment returns measurable group tightening of 0.2-0.3 MOA.
Specs at a glance
Pros & cons
What works
- 7075 T6 aluminum construction—62,000 psi yield strength exceeds MIL-SPEC
- 14.8 oz weight provides 18% more material at stress points than forged equivalents
- DPMS pattern compatibility verified against 12 component brands
- Raw finish allows for custom anodizing without stripping existing coating
Trade-offs
- No integrated jig system—adds $89-150 to total project cost
- Requires carbide end mills—standard HSS tools dull after 15 minutes of cutting
- Buffer tube threads may need chasing with 1-3/16"-16 tap due to shipping handling
- Fire control pocket depth requires precise measurement—varies ±0.008" across batch
Key attributes
| Material | 7075 T6 Aluminum |
| Type | 80% Lower Receiver |
| Caliber | .308 Winchester / 7.62x51mm |
| Platform | AR-10 / LR-308 |
| Finish | Unfinished (Raw Billet) |
| Weight | 14.8 oz |
| Length | 9.75 in |
| Width | 2.1 in |
Specifications
| Material | 7075 T6 Aluminum |
| Type | 80% Lower Receiver |
| Caliber | .308 Winchester / 7.62x51mm |
| Platform | AR-10 / LR-308 |
| Finish | Unfinished (Raw Billet) |
| Compatibility | DPMS-pattern |
| Jig Required | Yes (Separate Purchase) |
| FFL Required | No |
| Shipping | Same-day discreet shipping |
Best for
- Custom AR-10 rifle builds
- DIY firearms projects
- Platform for .308 caliber builds
Materials
- 7075 T6 Aluminum
What's in the box
- Unfinished 80% lower receiver
Care
Frequently asked questions
- Does this work with DPMS Gen 1 parts?
- Yes, the FrameSmith 308 billet maintains full DPMS Gen 1 compatibility. All pin locations match spec within 0.003 inch tolerance when measured against military drawings. You'll need a standard AR-10 lower parts kit like the one we offer.
- What jig is required for milling?
- The Polymer80 80% .308 Easy Jig Gen 1 is the tested compatible system. It provides guide bushings for 5/16" end mills and ensures proper fire control pocket depth of 0.860 inch. Allow 2-3 hours total setup and machining time for completion.
- How long does discreet shipping take?
- Orders ship same day via USPS Priority Mail, arriving in 2-3 business days. The package weight is 1.8 pounds including protective packaging, with exterior labeling indicating 'Machine Parts' only.
- Can I return it if I mess up the milling?
- No returns are accepted once machining has begun, as the product becomes unserialized firearm territory. We recommend practicing on aluminum scrap first—maintain spindle speeds below 2500 RPM to prevent chatter marks in critical areas.