Key points
General information
Enable the following compatibility settings for WH40K.exe located in <path-to-game>.
WH40K.exe
Compatibility mode Windows XP (Service Pack 2)
Run in 256 colors
Disable visual themes
Disable desktop composition
Disable display scaling on high DPI settings
Run this program as an administrator
WeapDef.dat
<path-to-game>\Data\
PlazPistHit.wav
PlazpistHit.wav
4 #Animation
5 #Animation
2 #Number of Sound Effects for Firing
1 #Number of Sound Effects for Firing
#
See https://www.youtube.com/watch?v=dbgp5kHheu8 for further fixes.