Fallout 4 enables mouse acceleration by default, and there’s no way to turn it off in-game. If you’re used to playing without acceleration enabled, as you would in most first-person shooters, you’ll want to turn this off.
To do so, you need to edit a config file outside the game.
Head on over to the following directory:
Edit the following file:
Under the [Controls] section of the document, add the following line:
That should do it.