Killshot is one of the companion perks in Fallout 4.
Obtaining
To gain the perk, the Sole Survivor has to reach maximum affinity with Robert Joseph MacCready, which is possible after completing his personal quest (Long Road Ahead).
Effects
The player character has 20% greater chance to hit an enemy's head in V.A.T.S.
Bugs
The original version of this perk granted 2000% increased accuracy, due to a typo, resulting in 95% Headshots at almost all times. It has since been corrected as of patch 1.3.