How to disable mouse acceleration?

I’m using Windows 8.1 x64

I’ve tried using the console to set “Mouse_Acceleration 0”, also tried making a .cfg file with the same setting. I tried negative values, but 0 was apparently the lowest. I’ve tried the MarkC Mouse Fix (which is a registry edit to remove acceleration from Enhance Pointer Precision in Windows which some older games forced on). I tried changing the polling rate of the mouse (I’ve experience it minimizes acceleration in some games).

I can not play a game with mouse acceleration, it’s unacceptable, so please, if someone knows how to disable it, I’d really appreciate it. I’ve spent hours now just trying to make the game playable. Finally found the HAC2 FoV fix, cause that starting FoV was also unacceptable. It’s so close to being playable, I can feel it!

Oh, I also tried to lock my framerate to 120 through nVidia Inspector in case the acceleration was due to mouse smoothing.