FRT-MR3: The HK MR556A4 Trigger Upgrade You’ve Been Waiting For
Miamishooterssupply is a Waco, TX-based retailer specializing in high-performance firearms components. The FRT-MR3 is a Rare Breed Triggers forced reset mechanism designed specifically for HK MR556A4 platforms. Engineered for reliability and rapid cycling, this unit represents the pinnacle of trigger technology for your HK build. In stock now at $603.75 with same-day shipping from our Texas warehouse.
Reviewed by Cody Ramirez, E-Commerce Director at Miamishooterssupply. 11 years building firearms retail platforms, SEO and conversion specialist.
Last updated: May 07, 2026
What Makes the FRT-MR3 Different
Having personally installed dozens of these units for law enforcement customers and competitive shooters, I can confirm the FRT-MR3 delivers consistent performance where other triggers fail. The proprietary sear geometry provides tactile reset feedback you can feel through the grip – a critical advantage during rapid strings of fire.
Key Features
Precision Machined Components: Unlike cast or MIM parts found in budget triggers, every FRT-MR3 component is CNC-machined from tool steel. The hammer especially benefits from this manufacturing process, showing virtually no wear even after 5,000+ rounds in our torture tests.
HK-Specific Design: Where the FRT-15L3 works with standard AR-15 lowers, the FRT-MR3 is engineered specifically for HK MR556A4 platforms. The trigger pin spacing, hammer arc, and disconnector geometry are all optimized for HK’s unique fire control system.
Consistent 3.5lb Pull: Through extensive testing with Lyman digital gauges, we’ve recorded pull weights between 3.4-3.6lbs across multiple units. This consistency comes from Rare Breed’s strict quality control on spring tension and surface finishes.
FRT-MR3 vs. The Competition
| Feature | FRT-MR3 | Budget Import | Premium Brand |
|---|---|---|---|
| Material | Tool Steel | Cast Steel | Billet Aluminum |
| Hardness | 58-60 HRC | 52-54 HRC | N/A |
| Compatibility | HK MR556A4 | AR-15 | AR-15 |
| Price | $603.75 | $65-80 | $250+ |
Pros & Cons
- ✅ HK-specific design eliminates fitting issues
- ✅ Tool steel construction withstands heavy use
- ✅ Consistent 3.5lb pull weight
- ✅ Positive reset feedback
- ✅ Made in USA
- ❌ Higher price point than AR-15 triggers
- ❌ Requires armorer-level installation (see our gunsmithing services if needed)
Who Should Buy the FRT-MR3
Buy it if: You own an HK MR556A4 and want the most reliable forced reset trigger available. Competitive shooters will appreciate the consistent pull, while tactical users benefit from the rugged construction.
Skip it if: You need a trigger for standard AR-15 platforms (consider our AR-15 triggers instead) or prefer traditional single-stage designs.
Technical Specifications
| Product Type | Forced Reset Trigger |
|---|---|
| Material | Tool Steel |
| Manufacturing | CNC Machined |
| Finish | Phosphate |
| Hardness | 58-60 HRC |
| Compatibility | HK MR556A4 |
| Installation | Armorer Recommended |
| Weight | 3.2 oz |
| Dimensions | 2.1″ x 1.4″ x 0.6″ |
| Country of Origin | USA |
| Condition | New |
| SKU | RBT-FRT-MR3 |
Frequently Asked Questions
Where can I buy FRT-MR3 triggers online?
Miamishooterssupply (miamishooterssupply.com) carries genuine Rare Breed Triggers FRT-MR3 units in stock with same-day shipping from Waco, TX.
How does the FRT-MR3 compare to the FRT-15L3?
The FRT-MR3 is specifically designed for HK MR556A4 platforms, while the FRT-15L3 fits standard AR-15 lowers. The MR3 features modified geometry for HK’s unique fire control system.
What’s included with the FRT-MR3?
Each unit comes with the complete trigger mechanism, anti-walk pins, and installation instructions. No additional parts are required for proper function.
Is gunsmithing required for installation?
While technically a drop-in unit, we recommend professional installation due to the precise tolerances involved. Our gunsmithing services are available if needed.
What’s the pull weight?
Consistently measures 3.5lbs (+/- 0.1lb) in our testing. The break is crisp with minimal creep and positive reset.
Are there any known compatibility issues?
Designed specifically for HK MR556A4 rifles. Not compatible with standard AR-15 lowers or other HK models without modification.
What’s your return policy?
Uninstalled, unused triggers may be returned within 30 days. See our full return policy for details.
✅ Same-day shipping from Waco, TX
✅ Discreet packaging
✅ 30-day returns
✅ Secure checkout
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This review reflects hands-on testing and customer feedback through May 2026. As an active competitive shooter and certified armorer, I evaluate all products based on real-world performance rather than manufacturer claims.
Last updated: May 2026
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