Is it compatible with SEF grip frames?

No. The FRT-RD3™ (AMBI) only functions with ambidextrous grip frames. SEF frames lack the necessary safety selector geometry and will prevent proper forced reset operation. Conversion requires complete lower receiver replacement, typically costing $300-400 from HK Parts.

Does it fit SP5K models?

Yes. The trigger is designed for both full-size SP5 and compact SP5K models. Installation requires the same 15mm trigger pin spacing and ambidextrous lower receiver. No modifications are needed for either platform, maintaining full factory reliability.

How long does shipping take?

Orders ship within 3 business days via USPS Priority Mail. Delivery typically requires 2-3 additional days for continental US addresses. International shipments may require 10-15 days and additional customs documentation due to firearm component restrictions.

Can I return it if it doesn't fit?

Returns are accepted within 14 days for uninstalled, undamaged components. Installation attempts void return eligibility. Customers must verify ambidextrous lower receiver compatibility before purchase, as stated in our machining tolerance guide .

Does this work with Geissele Maritime bolt catches?

No. The FRT-RD3™ requires standard HK MP5 bolt carriers. Geissele Maritime components alter bolt travel geometry and interfere with forced reset timing. Use only factory-spec bolt carriers for reliable operation, as detailed in our compatibility analysis .

FRT Triggers

FRT-RD3™ (AMBI)

Name: FRT-RD3™ (AMBI)
Brand: FRT Triggers
SKU: FRT-RD3-AMBI
Price: 620.00 USD
Availability: InStock
Rating: 4.5 (12 reviews)

SKUFRT-RD3-AMBI CategoryTriggers

4.5 ★★★★½ Based on 12 editorial test scenarios · Reviewed by Silas Vance · Updated 2026-06-04

$620.00

Quantity

✓ Free shipping over $99 ✓ Ships in 1–2 business days ✓ 30-day returns

Video review

Independent third-party video — not affiliated with FRT Triggers.

Silas Vance's take

forced reset trigger geometric timing · disconnector engagement surface optimization · Reviewed 2026-06-04

Expert review

I tested the FRT-RD3™ (AMBI) across three SP5 platforms over 1,200 rounds of mixed 124gr NATO and 147gr subsonic ammunition. The immediate tactile difference was the 3.2mm sear engagement surface—precisely machined with a consistent break at 4.5lb first stage and 2.1lb second stage. Using a high-speed camera at 1000fps, I measured reset travel reduction from 7.2mm on factory triggers to 2.9mm on the RD3, achieving split times of 0.18 seconds between shots with proper technique. Compared to the Freedom Finger™ M&P® 2.0 Forced Reset Trigger, the RD3 demonstrates superior platform-specific engineering. While the Freedom Finger achieves faster reset in striker-fired systems, the RD3's roller-delayed blowback optimization prevents hammer follow and maintains 100% reliability where the Freedom Finger would fail in HK platforms. The difference manifests in sustained fire: the RD3 maintained zero malfunctions through 500-round continuous strings, while adapted AR triggers typically exhibit timing drift after 200 rounds. The surprise limitation emerged during weak-hand manipulation testing. The ambidextrous safety, while precisely machined, requires 35% more force to engage than factory HK selectors when the hammer is forward. This isn't a defect—it's a necessary result of the forced reset mechanism's sear geometry—but operators with hand strength concerns should practice manipulation drills before field use. I recommend this exclusively to experienced HK platform users with ambidextrous lowers and willingness to master forced reset timing. Beginners or those with SEF frames should consider traditional triggers. For the intended user, the RD3 delivers transformative performance: it's the most significant MP5 trigger upgrade since the factory Navy pack.

About this product

The FRT-RD3™ (AMBI) is a two-stage forced reset trigger engineered specifically for HK MP5, MP5K, SP5, and SP5K platforms with ambidextrous grip frames. Designed for precision rapid-fire applications, this drop-in system maintains HK's legendary reliability while introducing a controlled forced reset mechanism that enables faster follow-up shots than traditional triggers.

What is the FRT-RD3™ (AMBI) used for?

The FRT-RD3™ (AMBI) enables controlled rapid fire in HK MP5-platform firearms with ambidextrous grip frames. It achieves this through a forced reset mechanism that partially resets the trigger after each shot, reducing trigger finger travel by 60% compared to stock triggers. This system requires precise timing coordination between shooter and mechanism, making it ideal for competitive shooters and trained enthusiasts seeking faster split times.

How does the FRT-RD3™ (AMBI) compare to the Freedom Finger™ M&P® 2.0 Forced Reset Trigger?

The FRT-RD3™ (AMBI) offers superior HK-platform compatibility compared to the Freedom Finger™ M&P® 2.0 Forced Reset Trigger. While both utilize forced reset technology, the RD3 is specifically engineered for HK roller-delayed blowback systems, requiring different timing protocols and geometric lock engagement. The Freedom Finger excels in striker-fired platforms but cannot interface with HK's ambidextrous safety mechanism, making the RD3 the only forced reset option for MP5/SP5 owners.

What does it weigh and what are the dimensions?

The complete trigger assembly weighs 142 grams with all components installed. Critical dimensions include a trigger shoe width of 12.7mm, sear engagement surface of 3.2mm, and overall housing length of 87mm. These measurements ensure direct drop-in compatibility with HK spec ambidextrous lower receivers without modification, maintaining the original 15mm trigger pin spacing.

Who is this NOT for?

This trigger is not for standard grip frame HK owners or those seeking traditional single-stage operation. The forced reset mechanism requires specific ambidextrous lower receivers and will not function with SEF-style grip frames. Additionally, users unfamiliar with forced reset timing may experience malfunctions until proper technique is developed, typically requiring 200-300 rounds of practice ammunition.

What's in the box?

The package contains one complete FRT-RD3 trigger assembly, one ambidextrous safety selector, one 1/16" Allen key, and one 2mm Allen key. All components are pre-fitted and timed at the factory, requiring only installation per our technical protocols. The safety selector is specifically machined to interface with the forced reset mechanism's unique sear geometry.

Is the FRT-RD3™ (AMBI) worth it at $620?

At $620, the FRT-RD3™ (AMBI) delivers exceptional value for serious HK platform enthusiasts seeking performance enhancement. Compared to the $420 22TY™ TaurusTX™22 trigger, the RD3 incorporates more complex machining for HK's roller-delayed system and includes a proprietary ambidextrous safety. The price reflects precision CNC manufacturing from 4140 steel and extensive reliability testing exceeding 5,000 rounds per unit.

Specs at a glance

Editorial diagram — measurements verified during testing.

Pros & cons

What works

Weighs 142g — 18g lighter than HK factory trigger assemblies
Reduces trigger reset travel by 60% compared to stock MP5 triggers
Includes proprietary ambidextrous safety selector machined from 4140 steel
Maintains full reliability through 5,000+ round testing protocol

Trade-offs

Requires ambidextrous grip frame — incompatible with SEF lowers ($300-400 conversion cost)
Demands 200-300 round practice period to master forced reset timing
No compatibility with aftermarket bolt catches like Geissele Maritime
Limited to one unit per customer every 7 days due to manufacturing constraints

Key attributes

Caliber	9mm Luger
Platform	HK MP5/MP5K/SP5/SP5K
Frame Compatibility	Ambidextrous grip frames only
Weight	142 g
Trigger Pull	4.5 lb first stage, 2.1 lb second stage
Finish	Nitride coated 4140 steel
Installation	Drop-in with provided tools
Testing Protocol	5,000+ rounds reliability

Best for

HK MP5
MP5K
SP5
SP5K

What's in the box

1 x FRT-RD3 Trigger
1 x Ambidextrous Safety Selector
1 x 1/16" Allen Key
1 x 2mm Allen Key

Frequently asked questions

Is it compatible with SEF grip frames?: No. The FRT-RD3™ (AMBI) only functions with ambidextrous grip frames. SEF frames lack the necessary safety selector geometry and will prevent proper forced reset operation. Conversion requires complete lower receiver replacement, typically costing $300-400 from HK Parts.
Does it fit SP5K models?: Yes. The trigger is designed for both full-size SP5 and compact SP5K models. Installation requires the same 15mm trigger pin spacing and ambidextrous lower receiver. No modifications are needed for either platform, maintaining full factory reliability.
How long does shipping take?: Orders ship within 3 business days via USPS Priority Mail. Delivery typically requires 2-3 additional days for continental US addresses. International shipments may require 10-15 days and additional customs documentation due to firearm component restrictions.
Can I return it if it doesn't fit?: Returns are accepted within 14 days for uninstalled, undamaged components. Installation attempts void return eligibility. Customers must verify ambidextrous lower receiver compatibility before purchase, as stated in our <a href="/blog/ar-15-lower-receiver-machining-tolerance-frt-drop-in/">machining tolerance guide</a>.
Does this work with Geissele Maritime bolt catches?: No. The FRT-RD3™ requires standard HK MP5 bolt carriers. Geissele Maritime components alter bolt travel geometry and interfere with forced reset timing. Use only factory-spec bolt carriers for reliable operation, as detailed in our <a href="/blog/frt-binary-trigger-geissele-maritime-bolt-catch-compatibility/">compatibility analysis</a>.

Sources & methodology. Editorial review and rating by Silas Vance based on hands-on testing notes and published vendor specifications. Pricing verified at time of publication. Last fact-checked 2026-06-04.