Last reviewed: 2026-04-17 by Jake Terry, FFL07/SOT3, with hands-on install experience on AR/AK/Glock platforms.
The Geissele MR556 Trigger is a two-stage trigger assembly engineered for the HK 556 and semi-auto HK 416 platforms. Based on the SSA design that defines Geissele’s reputation, it delivers a 2.75-3.0 lb first stage and a crisp 1.5-1.75 lb second stage break — total pull weight ranging from 4.25 to 4.75 lbs. Mil-spec pin sizes ensure drop-in compatibility, and the design requires the hammer to be cocked before the safety will engage, unlike the factory HK trigger system. Built for tactical shooters, law enforcement professionals, and precision shooters running HK rifles.
How It Works
The MR556 Trigger operates through a two-stage mechanism. The first stage offers smooth take-up at 2.75-3.0 lbs, transitioning to a crisp second stage that breaks at 1.5-1.75 lbs. The trigger uses mil-spec pin sizes and installs using standard punch-and-pin procedures for the HK 556 and semi-auto HK 416 platforms. After installation, cock the hammer to engage the safety — the safety will not engage with the hammer forward, a functional difference from the standard HK trigger system. Geissele manufactures this trigger with the same internal geometry and material specifications used in the SSA Trigger, ensuring consistent performance across platforms.
The Numbers
| Spec | Value |
|---|---|
| Type | Two-stage |
| Platform | HK 556, semi-auto HK 416 |
| Pull weight | 4.25-4.75 lbs total (1st: 2.75-3.0 lbs, 2nd: 1.5-1.75 lbs) |
| Pin | Mil-spec |
| Drop-in | Yes |
| Manufacturer | Geissele Automatics |
This trigger mirrors the geometry and function of the SSA Trigger, adapted for the HK 556 and semi-auto HK 416. For additional Geissele trigger options across AR and other platforms, see the full lineup.
Safe Handling & Compliance
Per current ATF guidance, this trigger is classified as a semi-automatic trigger assembly — each round fired requires a discrete trigger function, and the device does not convert a firearm to automatic fire. Regulatory status has changed before and may change again; verify current federal and state law before ordering.
- Follow the four rules of firearm safety at all times.
- Verify compliance with state and local laws regarding trigger modifications. Some jurisdictions restrict aftermarket trigger assemblies — confirm legality in your area before purchase.
- Install the MR556 Trigger using proper tools and procedures. Perform a function check before live fire, and confirm the safety engages only when the hammer is cocked. Improper installation can result in unsafe firearm operation.
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