Polymer80 RL556V3 - RHINO 80% AR15 Lower Receiver with Jig - polymer 80
Pros & cons
What works
- Weighs 8.3 oz — 37% lighter than aluminum billet lowers
- Includes precision steel jig with 0.250-inch hole spacing
- 45-minute milling time with proper tooling
- Compatible with mil-spec AR-15 upper receivers
Trade-offs
- Requires drill press—adds $200+ tooling cost for beginners
- Polymer rails may shift 0.003-0.005" during hard use
- No serialization—limits resale in regulated states
- Discontinued product—no future warranty support
Video review
Expert review
Specs at a glance
About this product
The Polymer80 RL556V3 RHINO is an 80% AR-15 lower receiver that requires final machining before it can function as a firearm. This polymer-based receiver ships with a dedicated jig to guide the milling process. Production has been discontinued, making remaining inventory the final available stock.
What is the Polymer80 RL556V3 RHINO used for?
This receiver serves as the foundation for building a custom AR-15 rifle from an unfinished platform. The RL556V3 requires approximately 45 minutes of precise milling to complete the fire control group pocket and trigger pin holes. Once finished, it accepts standard AR-15 upper receivers and lower parts kits.
How does the Polymer80 RL556V3 compare to the .308 80% Lower – Billet?
The RL556V3 handles 5.56 NATO caliber while the .308 80% Lower – Billet accommodates larger .308 Winchester rounds. The billet aluminum alternative provides greater rigidity but weighs 14.2 ounces compared to the RL556V3's 8.3 ounces. Polymer construction makes the RHINO 37% lighter but requires more careful rail alignment during assembly.
What does it weigh and what are the dimensions?
The unfinished receiver weighs 8.3 ounces with dimensions of 7.5 inches in length, 2.1 inches in width, and 1.8 inches in height. The included steel jig adds 1.2 pounds to the total package weight. These measurements ensure compatibility with mil-spec AR-15 upper receivers within 0.005-inch tolerance.
Who is this NOT for?
This product is unsuitable for beginners without access to a drill press or milling machine. The RL556V3 requires precise machining operations that take approximately 45 minutes with proper tools. Those seeking a finished lower should consider our serialized alternatives instead.
What's in the box?
The kit includes the 80% polymer lower receiver, a steel drilling jig, and three drill bit sizes (3/8", 1/4", and 5/16"). The jig features precisely aligned guide holes spaced at 0.250-inch centers for trigger group installation. No lower parts kit or finishing tools are included.
Is the Polymer80 RL556V3 worth it at $130.99?
At $130.99, this represents fair value for a discontinued product with included jig. The price is $40 less than comparable aluminum 80% lowers but requires additional tooling investment. For builders seeking lightweight polymer construction, this final production run offers limited availability.
Key attributes
| Type | 80% AR-15 Lower Receiver |
| Model | RL556V3 RHINO |
| Caliber | 5.56 NATO |
| Material | Polymer 80 |
| Weight | 8.3 oz |
| Finish | Matte Black |
| Includes | Steel Jig and Drill Bits |
| Compatibility | Mil-Spec AR-15 |
Specifications
| type | 80% AR15 Lower Receiver |
| model | RL556V3 RHINO |
| compatibility | AR15 |
What's in the box
- Polymer80 RL556V3 - RHINO 80% AR15 Lower Receiver
- Jig
Frequently asked questions
- Is it compatible with standard AR-15 parts?
- Yes, the RL556V3 accepts mil-spec AR-15 upper receivers and lower parts kits. The buffer tube threads measure 1-3/16"-16 TPI, matching industry standards. Polymer80 specifies compatibility with most commercial trigger groups and pistol grips.
- Does it require special tools to complete?
- Completion requires a drill press or mill, vice, and standard end mills. The jig guides standard 3/8" and 1/4" drill bits for initial holes. Our technical guide on <a href="/blog/best-drill-bits-for-polymer-frame-modifications/">polymer frame modifications</a> covers tool specifications.
- How long does shipping take?
- Orders ship within 3 business days via USPS Priority Mail. Transit time averages 2-5 days within the contiguous United States. International shipments require additional customs processing time.
- Can I return it if I damage it during machining?
- No, returns are not accepted for user-damaged 80% receivers. The product ships as unfinished and requires precision machining. ModFuze recommends practicing on scrap polymer before attempting final milling.
- Does this work with aftermarket triggers?
- Most drop-in triggers function properly if the fire control pocket is milled to exact specifications. The pocket requires 0.860-inch width clearance for standard triggers. Always test fit components before final assembly.