Killing Floor Headshot Mechanics: Detection, Multipliers and Decapitation

"Aiming for the head is a good idea. If you score a critical headshot, you can remove a Specimen's head, rendering them unable to use special abilities, and increasing any further damage they take."

• Killing Floor loading screen hint

This page explains how KF1 decides that a hit was a headshot and what follows, based on the Tripwire developer wiki and the KFMonster code it quotes.

A Scrake with debug collision drawn: the white cylinder is the collision cylinder, the blue sphere is the head area used for headshot checks. Image: Tripwire Interactive Wiki.

Who applies the multiplier

Usually the specimen applies the headshot multiplier when it takes damage. Three projectile classes do it themselves before calling the pawn's TakeDamage():

• CrossbowArrow (Crossbow)
• M99Bullet (M99)
• CrossbuzzsawBlade (Buzzsaw Bow)

The detection rules are the same either way.

Detection

1. Only damage types with bCheckForHeadShots=true are checked. Everything else does plain body damage.
2. A specimen that is already decapitated skips the check.
3. The game traces a line from the impact point on the collision cylinder and checks, with a line-sphere equation, whether it passes through the head sphere. The angle and the position you fired from do not matter, only whether the line crosses the sphere. Every shot hits the cylinder first, so every shot gets this test.
4. Melee weapons use a head area 25% larger, which is why knife, machete and katana headshots feel generous.

Dedicated servers guess where the head is

On a dedicated server the specimen's regular animations (walk, run, strafe) are not played server-side, so the server does not know exactly where the head is. It approximates:

• for falling, crouch-walking and swimming, it sets the animation to its midpoint;
• otherwise it shifts and scales the head sphere with two per-specimen values:

// KFMonster.uc, IsHeadShot()
HeadLoc = Location + (OnlineHeadshotOffset >> Rotation);
AdditionalScale *= OnlineHeadshotScale;

This is why headshots online can feel slightly different from solo: the server checks against an approximate head, not the one you see animating on your screen.

What a headshot does

1. Damage is multiplied by the damage type's HeadShotDamageMult, which already includes the current perk's headshot bonus (the Sharpshooter's is the best known).
2. The result is subtracted from the specimen's health and its separate head health.
3. If either reaches zero or below, the specimen is decapitated.
4. With a relevant weapon, the player's headshot counter goes up immediately (it feeds perk progress).

After decapitation

A headless specimen gets the BRAINS_Retarded intelligence level: it stumbles around, loses its special abilities (no Siren scream, no Husk fireball, no Fleshpound rage) and dies on its own after a set time. You can leave it and move on to the next target, unless it is still standing in a doorway your team needs.

For mutators: to check whether a monster still has its head, use the KFMonster.bDecapitated flag; if it is true, the monster has been decapitated (Dr_Killjoy's answer in the "Проверка на присутствие головы" (Checking whether the head is present) thread on the killingfloor.ru forum).

Practical takeaways

• Aim for the head sphere, not the model's face: the sphere is what counts, and online it sits where the server thinks the head is.
• Melee is forgiving on headshots: a 25% bigger target makes Berserker decapitations easier than they look.
• A decapitated Scrake or Fleshpound loses its special abilities and dies on a timer, so it is far less dangerous. Usually your next shots are better spent elsewhere.
• Player advice from the "Неполадки с Хэдшотами" ("Headshot trouble") thread on the killingfloor.ru forum: when crossbow bolts to the eye kept failing, players recommended aiming at the neck or slightly above it, or at the area between the mouth and nose, and noted that on a server with a different ping the hitboxes feel shifted, so it helps to remember where your shots actually land.