Keep in mind that the safety on an AR does not block the hammer from falling forward and striking the firing pin. All the safety does is block trigger movement. Why is that important to understand? Well... sear engagement works as the default drop-safety on a GI trigger. If you reduce sear engagement too much you increase the potential for the hammer to lose sear engagement and slam forward firing a round when the rifle is dropped or otherwise exposed to rough handling. Be cautious when tinkering with your trigger.

Here's an animation that explains how a GI trigger works.


Here's a vid of what the screw does...