I believe these are placed to make the sound played ( vanilla or otherwise ) a certain percentage quieter than normal. Sound files that contain more than one sound ( inserting the clip, then pulling the charging handle for reloading ) perhaps are used for the files containing two numbers following the file path.
I'm not completely sure of this, though I believe that I'm somewhat correct. Regardless, someone here must know.
Just another connoisseur of most things electronic.