You have mastered the firearm as a source of pain. With this Perk, any successful hit in combat with a ranged weapon will be upgraded to a critical hit if you also make a Luck roll.
”— Fallout and Fallout 2 description
Sniper is a perk in Fallout.
Any successful hit in combat with a ranged weapon will be upgraded to a critical hit if the player also makes a Luck roll. Combine with Better Criticals for improved effect!
Furthermore, it adds another Luck roll of (10*Luck). As a result, 10 LK means every hit is automatically a critical hit and More Criticals becomes useless.