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AS Designs

AS Designs ARHK Drop-In FRT Cassette

Self-contained drop-in forced reset cassette that runs in a stock HK roller-delayed housing across the MP5 and G3 families

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Quick Specs

Price
$550
Weight
4 oz
Brand
AS Designs
Category
trigger

Features

  • Drop-in cassette, stock OEM housing
  • 3-position (Safe/Semi/Active Reset)
  • Built on ARC-Fire technology
  • 9mm or .308 ejector included
  • Not compatible with CETME

Compatibility Tags

family: pccplatform: hk-sp5platform: century-ap5

Overview

The AS Designs ARHK is a self-contained drop-in forced reset cassette for HK roller-delayed guns, and it takes a different path from the rest of the MP5 forced reset field: no lower swap. The Mars unit ships a complete AR-FCG lower, and the Trinity and AS Designs trip-kit systems need an AR fire control group lower you build or buy. The Rare Breed FRT-RD3 is the one existing drop-in cassette, but it is limited to the 9mm MP5, MP5K, SP5, and SP5K. The ARHK installs directly into the factory OEM polymer housing with no modifications, no buffers, no auxiliary parts, and no external slip trip, and it spans the whole roller-delayed family. You keep your stock lower and drop the cassette in.

The cassette is built on the same ARC-Fire technology that runs the AS Designs forced reset selector, and it uses a three-position selector: Safe, a true disengaged Semi with a normal single-stage pull and no forced reset, and Active Reset in the third position where the ARC-Fire clutch engages. That disengaged semi is the practical differentiator over Super-Safety-based systems that keep the forced reset behavior live in the second position. The ARHK is aligned with Navy-style housing markings, with SEF support to follow, and is ambidextrous.

Fitment spans the roller-delayed family rather than a single host. The ARHK covers MP5, MP5K, AP53, G3/91, HK21, HK31, HK11, HK32, and HK33 clones and variants across both 9mm and .308, and it comes with your choice of a 9mm or .308 ejector to match the host. It works with all bolt carrier types. AS Designs is explicit that the ARHK will not run on CETME platforms for safety reasons. It is priced at $549.99, sold as a pre-order, with the first 1,500-unit batch scheduled to ship in early August 2026 after AS Designs completed torture testing across every listed platform. Verify current federal, state, and local law before purchase; forced reset triggers are banned or restricted in roughly fifteen states.

Key Features

  • Self-contained drop-in cassette; installs in the factory OEM polymer housing
  • No lower replacement, no external slip trip, no buffers or auxiliary parts
  • 3-position selector: Safe, true disengaged Semi, Active Reset
  • Built on AS Designs ARC-Fire forced reset technology
  • Aligned with Navy-style housing markings, SEF to follow; ambidextrous
  • Includes your choice of a 9mm or .308 ejector to match the host
  • Fits MP5, MP5K, AP53, G3/91, HK21, HK31, HK11, HK32, HK33 clones; not CETME

Pros

  • +Drop-in cassette keeps your stock lower; no AR-FCG lower to build or buy
  • +True disengaged semi mode with a normal pull, not a live forced reset second position
  • +Covers both 9mm and .308 roller-delayed hosts with a matched ejector
  • +Works with all bolt carrier types across MP5 and G3 hosts

Cons

  • Pre-order only; first drop not until early August 2026
  • $549.99 is near complete-lower pricing from Mars
  • Not compatible with CETME platforms
  • Forced reset triggers are banned or restricted in roughly fifteen states; verify local law first

Detailed Specifications

triggerType
Self-contained drop-in forced reset cassette (FRT) built on ARC-Fire technology
positions
3-position (Safe / disengaged Semi / Active Reset)
selector
Aligned with Navy-style housing markings, SEF to follow; ambidextrous
installation
Drop-in cassette into the factory OEM polymer housing; no lower replacement or slip trip
included
ARHK cassette with pre-installed ejector; choice of 9mm or .308 ejector
compatibility
MP5, MP5K, AP53, G3/91, HK21, HK31, HK11, HK32, HK33 clones and variants; all bolt carrier types; not compatible with CETME
availability
Pre-order; first 1,500-unit drop scheduled early August 2026
restrictedStates
Verify current federal, state, and local law before purchase; forced reset triggers are banned or restricted in roughly fifteen states

Compatible Platforms

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