Normally you can't use pistol whip in versions 1.0.4.0 and lower, this mod allows you to hit people with any gun in ALL versions
Side note: You can do this yourself by deleting a of couple numbers from one of the files to enable pistol whipping. It was always in the game but it was disabled until about version 1.0.5.0
Video of how to do it:
https://www.youtube.com/watch?v=yjysodDzyiw