Hair trigger does not and never has meant fires as fast as you can pull the trigger. It's a term taken from real life where all semi auto weapons fire as fast as you can pull the trigger. A gun with a hair trigger has a modified trigger system that allows the gun to fire with very, very little pressure applied to the trigger. It's called a hair trigger bc it's exaggerated that if a hair brushed the trigger it would fire. This allows the shooter to fire the weapon with much less anatomical movement. Less movement means less sway in the gun and more accuracy. It's wasted on a gun in a video game bc trigger pull and hand movement doesn't affect the virtual guns movement. In conclusion the perk does exactly what it's supposed to do.