RL556v3 80% AR15 Lower – White - polymer 80
Pros & cons
What works
- Weighs 9.8 oz — approximately 3 oz lighter than a comparable unfinished aluminum 80% lower
- White finish provides a base for custom cerakote or paint without requiring initial media blasting
- Costs $89 — a $25-$35 savings versus a basic anodized aluminum 80% lower from the same manufacturer
- Dimensional compatibility with mil-spec AR-15 components reduces fitment guesswork
Trade-offs
- No finishing jig included — adds a mandatory $60-$120 purchase and setup time before work can begin
- Polymer construction has a lower thermal deflection temperature than aluminum — sustained rapid fire can lead to point-of-impact shift
- White finish shows carbon fouling and handling marks more readily than black or FDE options
- Trigger pocket walls are thinner than aluminum — requires precise milling to avoid breaking into the safety selector hole
Video review
Expert review
Specs at a glance
About this product
The PolyLock RL556v3 80% AR15 Lower in White is an injection-molded polymer receiver blank that requires final machining and finishing by the end user to become a functional firearm component. It is one of five color options available for this specific model, designed for the AR-15 platform. This product represents a specific approach to receiver construction, balancing material properties against traditional alternatives.
What is the RL556v3 80% Lower used for?
This receiver blank is used to build a custom AR-15 by completing the final 20% of machining on the fire control group pocket and associated pin holes. It functions as the foundation of the rifle, housing the trigger, hammer, and magazine while serving as the attachment point for the upper receiver and stock.
The user must mill out the remaining material, drill three critical pin holes to a diameter of 0.154 inches (3.91 mm), and install a parts kit to create a working lower receiver. This process typically requires 60–90 minutes with a proper jig and router. For those unfamiliar with finishing, the Polymer80 Lower Receiver and Jig Kit provides a more complete starting package.
How does the RL556v3 compare to the .308 80% Lower – Billet?
The RL556v3 is designed for the AR-15/5.56 platform, while the .308 80% Lower – Billet is engineered for the larger, higher-pressure AR-10/.308 Winchester platform, making them incompatible. The .308 Billet model is also constructed from a different, likely aluminum, material versus the polymer construction of the RL556v3.
The RL556v3's polymer composition results in a lower raw material cost and reduced weight, approximately 9.8 oz compared to an aluminum lower's typical 12-14 oz. However, the billet aluminum alternative offers superior inherent rigidity and a higher perceived durability threshold for heavy-use applications, as discussed in our analysis on comparative noise and vibration damping.
What does it weigh and what are the dimensions?
The unfinished white RL556v3 blank weighs 9.8 ounces (278 grams) and has critical dimensions matching a mil-spec AR-15 lower receiver, specifically a buffer tube thread depth of 1.125 inches and a magazine well width of 1.175 inches. Its overall length is approximately 7.75 inches from the buffer tower to the tip of the trigger guard.
These dimensions ensure compatibility with standard AR-15 upper receivers, stocks, and grips once the finishing operations are complete and the fire control pocket is milled to a depth of 0.86 inches. The white color adds approximately 0.002 inches of coating thickness versus the raw polymer substrate.
Who is this NOT for?
This product is not for first-time builders lacking access to a drill press, mill, or compatible finishing jig and proper safety equipment. It is also unsuitable for individuals residing in jurisdictions where 80% receivers are regulated or prohibited, or for builders seeking a completed, serialized firearm component ready for immediate assembly.
Furthermore, it is not ideal for applications demanding extreme thermal stability or maximum rigidity under sustained automatic fire, where a forged or billet aluminum receiver like the anodized Fire/Safe Marked lower would be a more appropriate material choice.
What's in the box?
The box contains precisely one unfinished PolyLock RL556v3 80% lower receiver blank in white. It does not include a finishing jig, drill bits, end mill, installation tools, pivot/takedown pins, a parts kit (fire control group, buffer tube, etc.), or any assembly instructions.
The buyer must source these items separately. The receiver arrives with the trigger pocket, hammer pocket, and safety selector hole intentionally left solid, requiring the three critical pin holes to be drilled and the pockets milled out to a final depth as specified by the chosen jig's instructions. No hardware or packaging for anodizing is included.
Is the RL556v3 worth it at $89.00?
At $89.00, the RL556v3 is worth it for the builder who specifically wants a polymer, lightweight foundation for a non-duty AR-15 and is prepared to invest an additional $60-$150 in a quality jig and tooling. Its value is contingent on the user's ability to successfully complete the manufacturing process to precise tolerances.
The price represents a $10-$30 savings over a comparable unfinished aluminum blank, but this cost difference is often consumed by the specialized tooling required. For a builder who already owns a compatible jig, this represents a cost-effective way to build a dedicated lightweight or training rifle. Its value diminishes if the builder makes an error during machining, as the part cannot be re-used.
Key attributes
| Caliber | 5.56 NATO / .223 Remington |
| Platform | AR-15 |
| Material | Injection-Molded Polymer |
| Finish | White |
| Completion Status | 80% (Unfinished) |
| Weight | 9.8 oz (278 g) |
| Thread Pattern | Mil-Spec 1-3/16-16 |
| Magazine Compatibility | STANAG / AR-15 |
Materials
- polymer
Frequently asked questions
- Is it compatible with all AR-15 upper receivers?
- Yes, once properly finished, the RL556v3 is dimensionally designed to be compatible with any mil-spec AR-15 upper receiver. Ensuring a proper fit requires the user to mill the fire control pocket to the correct depth of 0.86 inches and drill the pivot and takedown pin holes precisely to 0.154 inches in diameter.
- Does it fit a standard AR-15 parts kit?
- Yes, it is designed to accept any standard AR-15 fire control group parts kit, bolt catch, magazine release, and pivot/takedown pins from vendors like Aero Precision, CMMG, or Palmetto State Armory. The user must mill the trigger and hammer pockets to the specific dimensions required for the chosen parts kit, typically using the included instructions from the jig manufacturer.
- How long does shipping take?
- Shipping typically takes 5-7 business days for processing and transit within the continental United States once the order is confirmed. Delivery times may extend to 10-14 business days for customers in Alaska, Hawaii, or during peak promotional periods. Expedited shipping options are sometimes available at checkout for an additional fee.
- Can I return it if I make a mistake during milling?
- No, PolyLock's policy explicitly states that 80% lower receivers cannot be returned once any machining, drilling, or finishing work has begun. The moment you alter the blank's original state, it is considered a custom-manufactured item and is not eligible for return, refund, or exchange. It is a final sale item.
- Does this work with a standard AR-15 buffer tube?
- Yes, the receiver's buffer tower is threaded for a standard mil-spec 1.125-inch buffer tube with a 1-3/16-16 TPI thread pattern. Once the finishing is complete, you can install any carbine or rifle-length buffer tube system that uses this thread specification.