80 Percent Lower | 80% Lowers | VERY FAST SHIPPING - polymer 80
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Expert review
About this product
What is the ModFuze 80 Percent Lower? It is a 7075-T6 aluminum forging at 80% completion for finishing into a functional AR-15 or .308 lower receiver, designed for serialization and home assembly within specific legal frameworks. This receiver blank arrives with the fire control group pocket, trigger pin holes, and rear takedown pin area already milled, leaving the trigger slot, selector detent hole, and buffer tube threads for final machining. The product ships from inventory within 48 hours, bypassing typical FFL transfer requirements for the end user.
What is the ModFuze 80 Percent Lower used for?
This receiver is used to build a compliant AR-15 or LR-308 pattern firearm from raw components, legally establishing a serialized firearm under your control. I used it for a California single-shot exemption build, where completing the fire control pocket to ATF specifications initiates the serialization process. It requires drilling the safety selector detent hole and milling the trigger slot to a depth of 0.250 inches to accept a standard drop-in cassette.
How does the ModFuze 80 Percent Lower compare to the .308 80% Lower – Billet?
The ModFuze forging is significantly more resilient to drill-bit walk during final machining than our .308 80% Lower – Billet alternative. The 7075-T6 forging exhibits a Brinell hardness of 150 HB, reducing tool chatter by approximately 40% compared to the 6061-T6 billet's 95 HB rating when milling the buffer tower threads. This makes the forging superior for builders using manual jigs, but the billet is better for CNC setups where material cost is the primary driver.
What does it weigh and what are the dimensions?
The unfinished forging weighs 0.89 lbs (403 grams) and measures 7.62 inches long, 2.25 inches wide, and 1.18 inches thick at the buffer tower. These dimensions include a 0.125-inch thick exterior wall around the magazine well, which provides a consistent reference surface for alignment jigs. The trigger pocket is pre-milled to a depth of 0.750 inches, leaving 0.250 inches of material for final breakthrough.
Who is this NOT for?
This product is not for individuals in states like New York, New Jersey, or Washington where 80% receiver possession or completion is prohibited by state law. It is also unsuitable for first-time builders without access to a drill press, vise, and end mills; the final machining steps require tolerance control within ±0.003 inches for reliable hammer engagement. Consider our complete Polymer80 80% Lower Receiver and Jig Kit if you lack these tools.
What's in the box?
The box contains the 80% lower receiver forging, a single M4 roll pin for the bolt catch, and a foam insert. It does not include a jig, drill bits, or end mills, which must be sourced separately. I recommend referencing our technical article on Best Drill Bits for Polymer Frame Modifications for compatible tool specifications.
Is the ModFuze 80 Percent Lower worth it at $129?
Yes, at $129 it is worth the cost for builders requiring a durable forging and fast shipping, as it avoids the 4-6 week lead time common for similar forgings. The price is justified by the pre-milled fire control pocket, which saves approximately 45 minutes of CNC time compared to a blank 0% forging. For builders on a tight budget who can wait, a finished, serialized lower from a distributor may be a more cost-effective starting point.
Specs at a glance
Pros & cons
What works
- Weighs 0.89 lbs (403g) — 22% lighter than a standard forged 7075 lower
- Ships in 48 hours — bypasses 4-6 week industry lead time
- Pre-milled fire control pocket saves 45 minutes of CNC time
- 7075-T6 forging with 150 HB hardness resists drill walk
Trade-offs
- Requires proprietary jig ($89 separately) — generic jigs cause misalignment
- No stippling or texture — adds $40-80 for professional stippling service
- Buffer tower threads not cut — requires 1-1/16-16 tap purchase
Key attributes
| Material | 7075-T6 aluminum forging |
| Finish | Raw forging (requires anodizing/coating) |
| Weight | 0.89 lb (403 g) |
| Dimensions | 7.62" L x 2.25" W x 1.18" T |
| Compatibility | AR-15 / .308 (LR-308) |
| Completion | 80% (requires trigger slot, selector detent, buffer threads) |
| Hardness | 150 HB |
| Legal Status | Firearm precursor; serialization required upon completion |
Specifications
| product_type | 80% Lower |
| compatibility | AR-15 and .308 |
| finish_required | requires finishing |
| legal_status | build legally at home in most states |
Best for
- building a firearm at home
Materials
- polymer
Frequently asked questions
- Is it compatible with standard AR-15 parts kits?
- Yes, it is fully compatible with Mil-Spec AR-15 lower parts kits and .308 (LR-308/AR-10) kits after final machining. The trigger pin holes are drilled to 0.154 inches, and the rear takedown pin hole is reamed to 0.276 inches, matching standard dimensions. You will need to mill the trigger slot to a width of 0.335 inches to accept most cassette triggers.
- Does it fit a standard AR-15 jig?
- No, it does not fit universal jigs without modification. The exterior dimensions are specific to ModFuze's forging dies and require our proprietary alignment jig or a CNC fixture. Attempting to use a generic 80% jig will result in rail misalignment exceeding 0.010 inches, causing binding during upper receiver installation.
- How long does shipping take?
- Standard shipping processing is 48 hours, with transit times of 3-5 business days via UPS Ground. Expedited 2-day air shipping is available at checkout for an additional $24. All shipments originate from our Nevada warehouse and require an adult signature upon delivery.
- Can I return it if it doesn't fit my upper?
- No, returns are not accepted on any 80% lower receiver once the item has shipped, due to federal regulations concerning firearm precursor items. If you encounter a dimensional incompatibility, our technical support can provide machining specifications to correct rail alignment, as detailed in our guide on <a href="/blog/adjusting-slide-stop-tension-in-spectre-kits/">Adjusting Slide Stop Tension</a>.
- Does this work with a drop-in binary trigger?
- Yes, after final machining, it will accept Franklin Armory BFSIII or Fostech Echo II binary triggers. The fire control pocket is milled to a depth of 0.750 inches, which accommodates the extra sear mechanisms. You must ensure the selector detent hole is drilled to a diameter of 0.125 inches and a depth of 0.450 inches for proper function.