From The Vault

Perk Steady Arm Fallout Tactics requirements: Level 4, ST 6, super mutant only ranks: 1 benefit: Burst Shot attacks cost one less action point

Steady Arm is a Fallout Tactics Perk. So far it hasn't appeared in any other game.

Your massive size means Burst Shot attacks cost one less action point. The official description indicates that this bonus is applied "while standing", but in Fallout Tactics 1.27 this perk makes burst shots cost one less action point regardless of stance.