FRT-RD3 AMBI

Two-Stage (3-Position) Forced Reset Trigger for the HK MP5, MP5K, SP5 & SP5K

FRT-RD3™ (AMBI) Overview

The FRT-RD3™ (AMBI) is a three-position forced reset trigger system designed for use with HK roller-delayed firearm platforms. Manufactured and assembled in the United States, the trigger assembly includes a three-position safety selector configured for HK ambidextrous (AMBI) grip frames.

Operating System

The FRT-RD3™ (AMBI) utilizes a forced reset mechanism that mechanically resets the trigger during the firearm’s operating cycle. The design requires a separate trigger pull for each round fired and incorporates three selector positions: Safe, Semi, and FRT.

Key Features

Three-Position Selector

The trigger system incorporates a three-position safety selector that allows users to select between Safe, Semi, and Forced Reset operating modes. The selector is designed specifically for HK-style ambidextrous grip frames.

Installation Design

The FRT-RD3™ (AMBI) is intended as a drop-in trigger assembly for compatible HK roller-delayed platforms. The included ambidextrous selector is designed to fit HK AMBI grip frame configurations.

Materials and Construction

The trigger assembly is manufactured using materials such as 7075 anodized aluminum and heat-treated 4140 steel. These materials are commonly used in firearm components because of their strength, durability, and wear resistance.

Platform Compatibility

The FRT-RD3™ (AMBI) is engineered for use with HK MP5, MP5K, SP5, and SP5K roller-delayed firearm platforms utilizing factory semi-automatic bolt carriers. According to the manufacturer’s specifications, the trigger is compatible with firearms that contain factory carrier-denial blocks and does not require permanent modifications for installation.

The system is also designed to function with full-auto style bolt carrier groups where legally possessed and applicable, although such carriers are not required for operation.

HK AMBI Grip Frame Identification

Compatible HK ambidextrous grip frames are commonly identified by modern pictogram markings rather than traditional letter markings. These grip frames typically feature controls on both sides and use visual bullet icons to indicate safety and firing modes. The selector indicator is located on the forward-facing portion of the selector axle.

Trigger Function and Operation

The FRT-RD3™ (AMBI) was developed specifically for roller-delayed firearm systems. The trigger geometry is designed around the operating characteristics of this platform. During operation, the trigger is mechanically reset as the action cycles and remains locked until the bolt carrier returns to battery. A new trigger pull is required for every shot fired.

The trigger assembly also incorporates a two-stage trigger pull design intended to provide a distinct take-up and break during operation.

Summary

The FRT-RD3™ (AMBI) is a specialized trigger system designed for HK roller-delayed firearm platforms, including the MP5, MP5K, SP5, and SP5K. Key characteristics include a three-position selector, forced reset operating mechanism, compatibility with HK ambidextrous grip frames, and installation without permanent firearm modifications on compatible platforms.