Sniper

Sniper is a perk in Fallout, Fallout 2, Fallout 3 and Fallout Tactics: Brotherhood of Steel.

Fallout, Fallout 2 and Fallout Tactics
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. It adds another luck roll of (10*Luck). 10 LK means every hit is automatically a critical hit.

Fallout 3
With the Sniper perk, your chance to hit an opponent’s head in V.A.T.S. is increased by 25%. As with most perks that increase your chance to hit in V.A.T.S., this bonus is multiplicative, not additive.