Gun Spread Formula

Spread = PerkModifiers(IronSightsBonus * CrouchBonus * (ConditionPenalty + SkillBonus) * (WalkPenalty + RunPenalty) + ArmPenalty)

PerkModifiers is a function that modifies the input value using any perks active on the actor that have a "Calculate Gun Spread" Entry Point and returns the result.

IronSightsBonus = fGunSpreadIronSightsBase + fGunSpreadIronSightsMult

• fGunSpreadIronSightsBase defaults to: 1.0
• fGunSpreadIronSightsMult defaults to: -0.65

  This value is 0 unless aiming with iron sights (holding the right mouse button with the default control scheme)

CrouchBonus = fGunSpreadCrouchBase + fGunSpreadCrouchMult

• fGunSpreadCrouchBase defaults to: 1.0
• fGunSpreadCrouchMult defaults to: -0.4

  This value is 0 unless the actor is crouched (sneaking)

ConditionPenalty = fGunSpreadCondBase + WeaponCondition * fGunSpreadCondMult

• fGunSpreadCondBase defaults to: 0.0
• fGunSpreadCondMult defaults to: 0.0
• WeaponCondition is the condition of the weapon equipped by the actor

  This value is 1.0 at 100%, 0.5 at 50% and 0.0 at 0%

SkillBonus = fGunSpreadSkillBase + ActorSkillValue * fGunSpreadSkillMult

• fGunSpreadSkillBase defaults to: 0.5
• fGunSpreadSkillMult defaults to: -0.0050
• ActorSkillValue is the actor's skill value for the skill used by the weapon.

  The skill value used is specified on the weapon form

WalkPenalty = fGunSpreadWalkBase + fGunSpreadWalkMult

• fGunSpreadWalkBase defaults to: 1.0

  This value is zero unless the actor is walking or not moving

• fGunSpreadWalkMult defaults to: 0.0

  This value is zero unless the actor is walking

RunPenalty = fGunSpreadRunBase + fGunSpreadRunMult

• fGunSpreadRunBase defaults to: 1.0

  This value is zero unless the actor is running

• fGunSpreadRunMult defaults to: 0.0

  This value is zero unless the actor is running

ArmPenalty = fGunSpreadArmBase + ArmCondition * fGunSpreadArmMult

• fGunSpreadArmBase defaults to: 0.5
• fGunSpreadArmMult defaults to: -0.5
• When using a one handed weapon, ArmCondition is 1 with a healthy right arm and 0 with a crippled right arm.
• When using a two handed weapon, ArmCondition is 1 with both arms healthy, 0.5 with 1 arm crippled, 0 with two arms crippled.

Minimum Spread

The gun spread value used by the game engine will never be less than the "Min Spread" value specified on the weapon form for the equipped weapon. If the value given by the formula is less than the "Min Spread" value, the value from the formula will be ignored and the "Min Spread" value for the weapon will be used instead.

Most weapons have a non zero value for "Min Spread". Therefore, no matter how skilled you are with the weapon or what perks you have, your weapon will always have a slight amount of spread. One notable exception to this are sniper rifles, which have 0 minimum spread, allowing weapon spread to be eliminated with a small guns skill of 100.

Notes

This formula has been derived by systematically tweaking the settings using the console and observing the effects on the magnitude of weapon sway.

Spread is also taken into account when determining VATS accuracy, and is the primary way that weapon skill affects VATS accuracy.

The default value of 1 for fGunSpreadWalkBase is important in this formula. Without it, the (WalkPenalty + RunPenalty) part of the equation would be 0 when not moving, negating the other spread calculations.

The "spread" value on the weapon form is ignored by the game engine. Only the "min spread" value is used.

Variables not used by this formula

These are variables that should logically have an impact on this formula but do not appear to have any effect on the player character's gun spread when tweaked. Further research into these settings should be performed. Perhaps they only effect NPC gun spread?

• fGunSpreadHeadMult
• fGunSpreadHeadBase
• fGunSpreadNPCArmBase
• fGunSpreadNPCArmMult
• fNPCMaxGunWobbleAngle

Other notable settings

fGunWobbleMultScope

Default value: 1.0

This setting controls how much scoped weapons will wobble when aiming with the scope, but it does not modify the weapon spread. If you modify some game settings to give the sniper rifle considerable wobble and set this setting to 0, the cross hairs will not wobble when you use the scope, but the bullets will still fly off course. Because of this, you should avoid modifying this setting, or else you will confuse players.