HOW TO INSTALL:
To Install simply run openIV and navigate to:

E:\Program Files\GTA_5\Grand Theft Auto V\x64\audio\sfx\WEAPONS_PLAYER.rpf\

and add the 'spl_railgun.oac' to the directory ! 

(You may need to use openFORMATS to import the file, to do this, run OpenIV and navigate to the directory shown above. Next click the edit button, once you have done that click the new button and hit 'Import using openFORMATS' once there locate the .oac file found it this folder and import it!)

THANKS AGAIN GUYS!

f0rest