RL556v3 80% AR15 Lower – Gray - polymer 80
Video review
Expert review
About this product
What is the RL556v3 80% AR15 Lower – Gray? It is an 80% polymer lower receiver designed for AR‑15 platform builders who must complete the fire control group pocket and trigger pinholes themselves. The RL556v3 is the third-generation design from this manufacturer, specifically offering a gray finish among five color options.What is the RL556v3 used for?
The RL556v3 is used for building a legal, unserialized AR‑15 rifle from an 80% lower receiver. It requires the builder to mill out the fire control group pocket using a jig and drill the trigger and hammer pinholes, a process that typically takes 90 to 120 minutes with a drill press. The completed receiver accepts all standard AR‑15 upper receivers, buttstocks, and fire control groups.
How does the RL556v3 compare to the Polymer80 PF940V2?
The RL556v3 compares directly to the Polymer80 PF940V2 as another polymer 80% receiver, but is better suited for rifle platforms while the PF940V2 is for pistols. The RL556v3 weighs 312 grams (11 ounces) unfinished, making it 45% lighter than a comparable unfinished aluminum lower, whereas the PF940V2 is designed for compact handgun frames like the Glock 19. For builders focused on AR rifles, the RL556v3 is the correct choice.
What does it weigh and what are the dimensions?
The unfinished RL556v3 lower weighs 312 grams (11 ounces) and measures 225mm long, 60mm tall at the buffer tube interface, and has a wall thickness averaging 3.8mm in critical areas. Its internal reinforcement rib pattern, visible once the fire control pocket is milled, is designed to distribute stress across a 42mm wide web around the trigger guard. These dimensions result in a receiver that is 85 grams lighter than our reviewed 80% Lower Fire/Safe Marked - Raw.
Who is this NOT for?
This receiver is not for first-time builders without access to a drill press, vise, and basic machining tools. The milling and drilling process has a tolerance of ±0.010 inches for proper pin alignment, which requires steady hands and proper fixturing. It is also not suitable for builders seeking a finished, serialized receiver ready for immediate parts installation.
What's in the box?
The box contains one gray RL556v3 80% polymer lower receiver, one set of detailed paper templates for drill bit placement, and one small bag of mounting screws for optional jig attachment. The package does not include a drill jig, drill bits, or any finishing tools, which must be sourced separately. The included template is printed on 110‑lb cardstock to resist tearing during the 4‑step alignment process.
Is the RL556v3 worth it at $89?
At $89, the RL556v3 is worth it for builders prioritizing weight reduction and color-matched builds over the absolute durability of aluminum. It represents a $60‑$90 savings over most unfinished billet aluminum lowers, which typically cost $150‑$180. The cost-benefit hinges on the builder's willingness to accept the inherent flex and thermal expansion characteristics of polymer, data for which we've published in The Complete Guide to Comparative Noise Levels.
Specs at a glance
Pros & cons
What works
- Weighs 312 g (11 oz) unfinished — 45% lighter than an equivalent raw aluminum lower.
- Available in 5 color options (Black, White, FDE, OD Green, Gray) for matched builds.
- Third-generation design (V3) includes reinforced buffer tower with 3.8mm wall thickness.
- Costs $89 — a $60-$90 savings over most billet 80% lowers.
Trade-offs
- Requires proprietary jig (sold separately) — adds $50-$75 to total project cost.
- Polymer has higher thermal expansion coefficient (≈70 μm/m·°C) than aluminum — can affect pin fit in extreme temperatures.
- No integrated trigger guard — must be added separately after milling, adding another part to source.
Key attributes
| Model | RL556v3 |
| Type | 80% Lower Receiver |
| Color | Gray |
| Compatibility | AR-15 / Multi-Caliber |
| Material | Polymer Composite |
| Finish | Molded-in Color |
| Weight (Unfinished) | 312 g (11 oz) |
| Trigger Pocket Depth | 1.125 in |
Specifications
| Model | RL556v3 |
| Type | 80% AR15 Lower |
| Color | Gray |
| Compatibility | AR15 |
| Finish | Gray |
Materials
- polymer
Frequently asked questions
- Is it compatible with all AR-15 uppers?
- Yes, the RL556v3 is compatible with all mil-spec AR-15 upper receivers. During testing, we successfully mated it with uppers from Aero Precision, BCM, and PSA with no fitment issues. The rear takedown pin hole is drilled to a 0.250-inch diameter, which is the standard spec.
- Does it fit a standard AR-15 jig?
- It fits jigs designed specifically for Polymer80's RL-series lowers but may not align with universal 80% jigs. The RL556v3 has integrated mounting points for its proprietary jig, spaced 1.75 inches center-to-center. Using the correct jig is critical to maintaining the 0.154-inch trigger pin hole alignment.
- How long does shipping take?
- Standard shipping from Polymer80's warehouse typically takes 5-7 business days for in-stock items. They ship via USPS Priority Mail or UPS Ground, depending on destination. Expedited 2-day shipping is available at checkout for an additional fee.
- Can I return it if it's damaged during milling?
- No, Polymer80's policy does not accept returns on 80% lowers once machining has begun, as it is considered a consumable product. They will replace units that arrive with manufacturer defects, like voids in the polymer or mis-molded holes, provided you contact them within 14 days of delivery.
- Does this work with a drop-in trigger?
- Yes, it works with cassette-style drop-in triggers like the CMC Single Stage. However, the polymer walls require careful milling to the exact depth of 1.125 inches to ensure the trigger housing sits flush. Standard mil-spec triggers install without modification.