Geissele HK MR 5.56 Trigger 05-220 is similar to Geissele's SSA Trigger and can be used in both the HK 556 and semi-auto HK 416's. It's not compatible with the MK4. This two-stage trigger breaks a total of 4.25 to 4.75 lbs, split between a 2.75 to 3.0 lb first stage and a 1.5 to 1.75 lb second stage. That two-stage design gives a smooth takeup followed by a clean break, the same fundamental feel Geissele's AR-platform SSA triggers are known for, adapted specifically to fit the HK trigger pack. One important operational note: after installing this Geissele Trigger, the hammer must be cocked to engage the safety, unlike HK's factory trigger system where the selector can be placed on Safe with the hammer forward. This Geissele HK trigger is designed to work with a mil-spec 90-degree safety, and compatibility with short-throw safeties on A4-series rifles isn't confirmed. Key Features: Two-stage, non-adjustable, drop-in design Total pull weight: 4.25–4.75 lbs First stage: 2.75–3.0 lbs Second stage: 1.5–1.75 lbs Fits HK MR556 and semi-auto HK 416 Not compatible with the MK4 Designed for mil-spec 90-degree safety Requires hammer cocked to engage safety after install Built for shooters who want the same crisp break the SSA Trigger delivers on AR platforms, now running on an HK trigger pack instead. Geissele Automatics Geissele HK MR 5.56 Trigger 05-220