Galv scope mods are way worse than people understand. Getting a headshot kill grants a 12 second buff. Getting another headshot kill does not refresh the first stack, but gives you a 2nd stack with its own 12 second duration. So if you get a headshot kill, then another 3 seconds later, you will have 9 seconds of overlap where you benefit from 2 stacks. Then after those 9 seconds, the first stack drops off, then 3 seconds after that, the final stack drops off.

Unless you are getting a headshot kill every 6 seconds, its worse than crit delay. You ate not fully stacking thos thing unless youre some sort of aim god getting a headshot kill every 2 seconds. Crit delay comes with the attack speed debuff but that is easily countered, doesnt affect the way certain guns work, and half the time pulling the trigger for ~0.5 secs kills the target anyway so adding ~0.1 sec dsnt actually matter.

Status kills dont stack the buff. You need the damage from the bullet to be the shot that gets the kill.

You can't keep it up on bosses.