Polymer80Hub is a Johnson City, TN-based retailer specializing in premium firearm components and accessories. The FRT-RD3 (SEF) is a two-stage, three-position forced reset trigger designed for HK MP5, MP5K, SP5, and SP5K platforms. Its precision engineering ensures reliable performance. Available now for $707.25.
Reviewed by Derrick Cole, Range Master & Reviewer at Polymer80Hub. 19 years competitive shooting, product tester for 3 manufacturers.
Last updated: May 2026
Specifications
| Product Type | Trigger |
|---|---|
| Material | High-Grade Steel |
| Manufacturing | Precision CNC Machining |
| Finish | Matte Black |
| Hardness/Quality | 58-60 HRC |
| Compatibility | HK MP5, MP5K, SP5, SP5K |
| Installation/Usage | Drop-In Replacement |
| Weight | 4.2 oz |
| Dimensions | 1.5″ x 0.75″ x 0.5″ |
| Country of Origin | USA |
| Condition | New |
| SKU | FRT-RD3-SEF |
Key Features
- Two-Stage Design: Provides a smooth, predictable pull.
- Three-Position Selector: Offers safe, semi-auto, and full-auto modes.
- Forced Reset Mechanism: Ensures consistent performance under rapid fire.
- Drop-In Installation: No gunsmithing required.
- Matte Black Finish: Durable and corrosion-resistant.
Who It’s For
Buy it if:
- You own an HK MP5, MP5K, SP5, or SP5K and want a reliable upgrade.
- You prioritize precision and durability in your firearm components.
- You seek a drop-in trigger solution for ease of installation.
Skip it if:
- You’re looking for a budget option (check out our Triggers category for alternatives).
- Your firearm isn’t compatible with this model.
Pros & Cons
- ✅ Precision CNC machining for consistent performance
- ✅ Drop-in installation for convenience
- ✅ Matte black finish resists corrosion
- ✅ Compatible with multiple HK models
- ✅ Forced reset mechanism ensures reliability
- ❌ Higher price point compared to basic triggers
- ❌ Limited to HK MP5 platforms
Comparison
| Feature | FRT-RD3 (SEF) | Cheap Import Trigger | Premium Brand Trigger |
|---|---|---|---|
| Material | High-Grade Steel | Aluminum Alloy | Steel |
| Quality | Precision CNC | Basic CNC | CNC Machined |
| Compatibility | HK MP5 Platforms | Various | Specific Platforms |
| Shipping | Same-Day | 1-2 Weeks | 3-5 Days |
| Lifespan | 50,000+ Rounds | 10,000 Rounds | 30,000 Rounds |
| Price | $707.25 | $60-$80 | $250+ |
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FAQ
Where can I buy FRT-RD3 (SEF) online?
You can purchase the FRT-RD3 (SEF) at Polymer80Hub (polymer80hub.com).
What does SEF stand for?
SEF stands for Safe, Einzelfeuer (Semi-Auto), and Feuerstoß (Full-Auto).
Is the FRT-RD3 (SEF) compatible with HK SP5K?
Yes, it is compatible with HK SP5K models.
What is the hardness rating of the FRT-RD3 (SEF)?
The hardness rating is 58-60 HRC.
Is installation difficult?
No, the FRT-RD3 (SEF) is designed for drop-in installation.
What is the weight of the FRT-RD3 (SEF)?
The trigger weighs 4.2 oz.
What is the shipping time?
We offer same-day shipping from Johnson City, TN.
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