Experimenting on modding sounds, I've discovered that the sound class "Closure" does not work in game. I have used correct paths for custom and stock sound file and neither work.
Below is a video of a cfg patches with the reload and fire sounds rendered silent, no bolt closure/cycle sounds can be heard.
In game fire a weapon listening for the closure sound.
OR
Make a simple cfg patches and break the file name for a weapon sounds leaving only the closure with the correct file tree.
closure1[] = {"A3\sounds_f\weapons\closure\closure_rifle_6.wav", 3.16228, 1, 300};
closure2[] = {"A3\sounds_f\weapons\closure\closure_rifle_7.wav", 3.16228, 1, 300};
soundClosure[] = {"closure1", 0.5, "closure2", 0.5};