Concentrated Fire

Concentrated Fire is a Fallout 3, Fallout: New Vegas and Fallout 4 perk.

Fallout 3 and Fallout: New Vegas
Each successive time you target the same body part in V.A.T.S., your chance-to-hit raises by +5%. So, if your first to-hit was 40%, 2nd would be 45%, 50%, etc. This can lead to very easy head-shots when teamed with other to-hit % boosters (Sniper, Commando, etc.)