Killing Floor Mouse Fix & Acceleration Guide

Killing Floor 1 (running on Unreal Engine 2.5) suffers from notorious mouse acceleration and “floaty” input issues on modern Windows systems. If you feel like your aim is inconsistent or the crosshair “drifts” after you stop moving the mouse, you need to apply these fixes.

The “Floaty” Aim Problem

By default, Killing Floor applies mouse smoothing and acceleration that was designed for older ball mice and Windows XP. On Windows 10/11 with high-DPI optical sensors, this results in negative acceleration (your turn speed is capped) or inconsistent sensitivity.

Step 1: Edit User.ini (The Most Important Fix)

The in-game menu does not show all mouse settings. You must edit the configuration file manually.

1. Navigate to your Killing Floor System folder:
   • Usually: C:\Program Files (x86)\Steam\steamapps\common\KillingFloor\System\
2. Find the file User.ini and open it with Notepad.
3. Search for [Engine.PlayerInput].
4. Change (or add) the following lines to match these values exactly:

ini
[Engine.PlayerInput]
MouseSmoothingMode=0
MouseSmoothingStrength=0.000000
MouseAccelThreshold=0.000000
DoubleClickTime=0.250000

5. Search for [Engine.Input].
6. Ensure MouseSamplingTime is low (default is usually fine, but check for weird values).

Disable Acceleration in Input Section

In the same User.ini, verify these additional lines under [Engine.PlayerInput]:

ini
bEnableMouseSmoothing=False

Step 2: Windows Pointer Precision

Killing Floor respects Windows mouse settings.

1. Open Windows Mouse Settings.
2. Click Additional mouse options.
3. Go to the Pointer Options tab.
4. Uncheck “Enhance pointer precision”.
5. Set the slider to the 6th notch (middle).

Step 3: Launch Options (Optional)

In your Steam Library:

1. Right-click Killing Floor.
2. Select Properties.
3. In Launch Options, add: -noforcemparms -noforcemaccel

Note: These commands are from the GoldSrc/Source engine era but some users report they help override Windows settings for older Unreal games too.

Step 4: High Polling Rate Fix

If your mouse runs at 1000Hz or higher, KF1 might stutter when looking around.

• Symptoms: Frame rate drops when moving the mouse quickly.
• Fix: Lower your mouse polling rate to 125Hz or 500Hz in your mouse software (Logitech G Hub, Razer Synapse, etc.). Unreal Engine 2 struggle with high polling rates.

Testing Your Aim

After applying these fixes, jump into a solo game (or join our servers).

• Perform a 360-degree turn. It should take the exact same distance on your mousepad every time, regardless of how fast you move the mouse.
• If your aim feels “snappy” and raw, the fix worked.