I know you can spare them in VATS, but from reading around, they can also appear during the use of VATS without noticing. Is this true? So guaranteed hits without triggering the critical-bar in VATS? On the other side, wearing luck armor would dramatically boost you char then.
Outside of VATS, the pling sound tells you that a critical hit happened, but people claim that it is completely separate from all luck-based perks (critical damage improvement for instance).
Wikia is sadly very vague on this topic. Almost no "in-depth" info.
Best Answer
Unlike earlier FO games, there is no chance based critical hit system in FO4. The only exception (to my knowledge) is the chem Overdrive which adds +25% critical hit chance, which can make critical hits occur outside of VATS or inside VATS without a full crit meter.