Provide the Left 4 Dead Beta weaponsounds from the game version 2007.
Install: Unzip with with 7Zip or 7zip arcive compatible software the file.
Copy and Paste the folders in: left4dead/left4dead/sounds/weapons/
Make sure you overwrite them all. MAKE BACKUP BEFORE IF YOU WANT!
Start the game and run this cvar in console: snd_rebuildaudiocache
wait for finish, game should close auto if not write quit in console. Restart and you're done.