This perk allows you to pull the trigger a little faster and still remain as accurate as before. Each ranged weapon attack costs 1 AP less to perform.”— Fallout 2 In-game description
AP costs for all ranged attacks, including thrown weapons, are reduced by one point. This allows the player character to make more attacks per turn and reload sooner.
The Fallout manual erroneously states that the Perception requirement is 4.