The higher your accuracy, the higher your chance to hit a headshot, and lower chance of hitting legs.
Your operator can have an accuracy value of 0-48 and your weapon can multiple that accuracy up to 2x. So the max accuracy you can have during combat is 96.
At 0 accuracy, you have a 33.33% chance to hit an enemy in the head, body, or legs.
Let us say your character has an accuracy of 5 and your sweet sniper multiples that by 2x. In combat, you'll have 10 Accuracy points. The chance of you hitting an enemy's legs decreases by 10%, and the chance of you hitting an enemy in the head and body increases by 5% respectively.
Now, what happens once there is no longer a chance to hit an enemy in the leg? We begin to decrease the chance of hitting an enemy in the body and increase the chance of hitting the enemy in the head.
Let us assume our combat accuracy (Operator Accuracy * Weapon Accuracy Multiplier) is equal to 70. We start by deducting the 33% chance of hitting the enemy in the legs.
After reducing the chance of hitting legs by 33, we are leftover with 37 accuracy points. We then subtract these from the chance of hitting the body and add them to the chance of hitting the head.
Accuracy skills with your operator as you level up. You get a big bonus during the early levels and then get some diminishing returns as you reach the max level.
Y= Accuracy, X=Operator Level