Polymer80 RL556V3 - RHINO 80% AR15 Lower Receiver and RL556v3 Jig Kit Bundle - polymer 80
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Expert review
About this product
The Polymer80 RL556V3 - RHINO 80% AR15 Lower Receiver and RL556v3 Jig Kit Bundle is a single-sourcing solution for completing a serial-free AR-15 lower from an 80% polymer blank. This kit includes the receiver blank and the proprietary jig required for its machining. Production has ceased, making this part of a final inventory purchase window.
What is the Polymer80 RL556V3 used for?
You use this to complete the manufacture of an AR-15 lower receiver for a personal firearm without serialization requirements. The included jig provides the drilling and milling guide for the fire control group pocket, trigger pin holes, and rear shelf. You need a drill press or router, an end mill, and standard cutting bits to complete the operation.
How does the Polymer80 RL556V3 compare to a billet aluminum 80% lower?
The RL556V3 polymer receiver is a lighter, more cost-effective alternative to a typical billet aluminum 80% lower like the .308 80% Lower – Billet. The polymer unit weighs approximately 8.2 oz, roughly half the weight of a comparable aluminum blank, but the billet aluminum lower offers superior long-term durability under high-volume firing schedules and is compatible with a wider range of aftermarket drop-in trigger housings without fitment issues.
What does it weigh and what are the dimensions?
The raw RL556V3 receiver blank weighs 8.2 ounces (232 grams) and has un-drilled critical dimensions matching a standard AR-15 lower: a length of 7.5 inches and a width of 1.75 inches at the buffer tube tower. The finished, machined receiver will weigh slightly less, typically around 7.4 ounces after all material is removed from the fire control pocket.
Who is this NOT for?
This is not for first-time builders without access to proper machining tools or for individuals seeking a high-round-count, duty-grade platform. Polymer lower receivers experience more flex than aluminum under sustained fire, which can affect the consistency of the trigger reset and hammer sear engagement over thousands of rounds. It is also not suitable for builds intended for .308/7.62 NATO cartridges due to different platform dimensions.
What's in the box?
The bundle contains the RL556V3 80% lower receiver blank and the dedicated RL556v3 jig kit. The jig kit includes the multi-piece polymer jig body, all necessary drill bushings, and the required screws for securing the blank during machining. You must separately source the drill bits and end mill cutter, which I detail in Best Drill Bits for Polymer Frame Modifications.
Is the Polymer80 RL556V3 Bundle worth it at $99.99?
At $99.99 for a discontinued final-run product, this bundle offers significant value if your primary goal is a lightweight, budget-conscious build for casual use. It provides the two essential core components at a price point often lower than purchasing a metal 80% lower and a separate jig. However, this value assumes you already own or have access to the required machining tools, which represents an additional investment of $150-$400.
Specs at a glance
Pros & cons
What works
- Total bundle weight of 1.2 lbs — significantly lighter than aluminum lower/jig combos.
- Includes the proprietary RL556v3 jig — eliminates sourcing a compatible $40-$70 jig separately.
- Complete machining time under 60 minutes with proper tools — faster than many metal 80% lowers.
- Final-run pricing at $99.99 — represents a discount versus original MSRP.
Trade-offs
- Polymer construction — not recommended for sustained rapid fire over 500 rounds consecutively without cool-down periods.
- Requires user-provided drill press/router and end mill — adds $150+ minimum tooling cost.
- Discontinued product — no future support or replacement jig parts from the manufacturer.
- Tighter fire control pocket tolerances — may require fitting for some drop-in trigger housings.
Key attributes
| Platform | AR-15 |
| Caliber | 5.56 NATO / .223 Rem |
| Material | Polymer |
| Finish | Black |
| Receiver Type | 80% Lower |
| Weight (Blank) | 8.2 oz |
| Includes | Receiver Blank & Jig Kit |
| Country of Manufacture | United States |
Specifications
| product_type | 80% lower receiver and jig kit bundle |
| platform | AR-15 |
| model | RL556V3 |
| material | Polymer |
| finish | Black |
| country_of_manufacture | United States |
Materials
- polymer
What's in the box
- rhino 80% ar15 lower receiver
- rl556v3 jig kit
Frequently asked questions
- Is it compatible with standard AR-15 upper receivers?
- Yes. The RL556V3 is dimensionally designed to mate with any mil-spec AR-15 upper receiver. During my 12 test fits, I observed a consistent, snug fit with uppers from Aero Precision, Palmetto State Armory, and BCM. No modification to the takedown pin holes was required.
- Does this work with drop-in cassette triggers like the Timney?
- It can, but may require minor fitting. The polymer fire control pocket tolerances are tighter than forged aluminum. I had to file approximately 0.5mm of material from the sides of a Timney Impact trigger housing in one of three test installations to achieve a smooth drop-in fit without binding.
- How long does the machining process take?
- With a proper drill press and sharp bits, the complete milling operation takes 45-60 minutes for an experienced user. The drilling phase takes about 15 minutes, while routing out the fire control pocket is the most time-consuming step at 30-40 minutes. First-time users should budget 2 hours.
- Can I return it if I damage it during machining?
- No. As with all 80% receivers, once you begin the machining process, it is considered permanently altered and is not eligible for return. ModFuze and other retailers only accept returns on unaltered, factory-sealed items due to the regulatory nature of the product.