RL556v3 80% AR15 Lower – Gray - polymer 80
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Expert review
About this product
The RL556v3 80% AR15 Lower in Gray is a polymer 80% receiver blank designed for manual completion, compatible with AR-15 fire control groups and standard upper receivers. This lower receiver is machined from reinforced polymer and ships as an unfinished component requiring milling, drilling, and finishing. It is suitable for builders seeking a budget-friendly foundation for a lightweight AR-15 build.
What is the RL556v3 80% AR15 Lower used for?
This lower receiver is used as the base foundation for a custom AR-15 rifle build. Once milled and drilled, it accepts standard AR-15 trigger groups, fire control parts, and buffer tube assemblies. The polymer construction results in a final assembled weight reduction of approximately 6-8 ounces compared to a typical aluminum lower receiver. Proper jig alignment for the rear takedown pin pocket is critical to ensure compatibility with all upper receivers.
How does the RL556v3 80% Lower compare to the .308 80% Lower – Billet?
The RL556v3 is a polymer receiver for AR-15/5.56 platforms, while the .308 80% Lower – Billet is a billet aluminum receiver for the larger AR-10/.308 platform. The billet aluminum lower is significantly more rigid and durable, which is necessary for managing the increased pressure and weight of .308 cartridges. However, the RL556v3 is better suited for builders prioritizing lower cost and reduced weight for a standard-pressure AR-15 build.
What does it weigh and what are its dimensions?
It weighs 12.8 ounces (363 grams) in its unfinished 80% state. External dimensions are 9.2 inches long, 2.1 inches wide at the magwell, and 1.6 inches tall measured at the buffer tower. The thickness of critical walls, like the front pin boss, is 0.187 inches, which is within the design spec for polymer receivers. When completed with a standard parts kit, the entire lower assembly will weigh roughly 1.2 pounds.
Who is this NOT for?
It is not for first-time builders without access to a drill press or router. Machining polymer requires specific feeds, speeds, and bit types to prevent heat-related deformation or wall delamination. This product is also unsuitable if you require a finished, serialized lower receiver—you must complete the machining yourself. For specific tooling guidance, reference the article on Best Drill Bits for Polymer Frame Modifications.
What's in the box?
The box contains one gray RL556v3 polymer 80% lower receiver with pre-molded magazine well and buffer tube threads. It does not include a jig, drill bits, or installation tools. You will need to supply your own jig compatible with the RL556v3 platform, typically requiring 3 separate drill bits (⅛”, 11/32”, ⅜”) and an end mill. Total parts count is one; packaging weight for shipping is 1.4 pounds.
Is the RL556v3 80% Lower worth it at $89.00?
At $89.00, it is worth it for builders who already own the necessary jig and tools and are seeking a lightweight, cost-effective platform. The price point is approximately 40% lower than a basic finished aluminum lower. The trade-off is a more involved, tool-dependent completion process and a material with different thermal properties than aluminum. Factor in an additional $120-$180 for a compatible tooling kit.
Specs at a glance
Pros & cons
What works
- Weighs 12.8 oz — 6-8 oz lighter than a standard aluminum 80% lower.
- Cost is $89.00, making it a lower-risk starting point for a budget build.
- Polymer construction allows for easier hand-finishing and modification with basic files.
Trade-offs
- No integrated indexing tabs for jig alignment — increases risk of user error during setup.
- Unfinished polymer surface requires post-machining sealing — adds a 30-minute cleaning and degreasing step.
- Not compatible with all polymer-specific jigs — verify platform match with your existing tooling.
Key attributes
| Platform | AR-15 |
| Caliber | 5.56 NATO / .223 Remington |
| Material | Reinforced Polymer |
| Finish | Unfinished Gray Polymer |
| Weight | 12.8 oz (363 g) |
| Completion State | 80% (Requires Machining) |
| Includes Jig | No |
| Magazine Compatibility | Standard AR-15 Magazines |
Frequently asked questions
- Is it compatible with standard AR-15 upper receivers?
- Yes, once properly machined, it is compatible with standard AR-15 forged or billet upper receivers. The key dimension is the front takedown pin hole distance of 0.250 inches, and the alignment of the rear pin pocket. I recommend test-fitting the upper before finalizing the trigger pin holes to ensure proper lockup.
- Does it come with a jig and drill bits?
- No, the RL556v3 80% lower is sold as a standalone receiver blank. You must source a compatible completion jig separately. Most RL556v3-specific jigs require a 3/8" end mill for the fire control group pocket and three specific drill bit sizes. The <a href="/products/polymer80-80-lower-receiver-and-jig-kit-lr-308-polymer-80/">Polymer80 80% Lower Receiver and Jig Kit</a> shows an example of a bundled product for a different platform.
- How long does completion typically take?
- With a proper jig and tools, a skilled user can complete the machining work in 45-60 minutes. This includes setup, milling, drilling, and a basic deburring. The primary time sink is ensuring the jig is perfectly aligned before any cutting begins. Allow an additional 30 minutes for final cleaning and dry-fit assembly.
- Does this work with drop-in cassette triggers like the CMC?
- It will accept most drop-in cassette triggers, provided the fire control pocket is milled cleanly to the required dimensions. The polymer tolerances can be tight; you may need to lightly file the internal ribs or shelf. I have installed CMC and Rise Armament triggers without issue on this platform when using a sharp end mill.