I assume you're wanting to edit the "sound name" that a certain projectile has? The projectile and hardpoint scripts reference a file called "StaticDefs.py", which IIRC, is located in the main scripts directory. The file then pairs this "sound name" with the filename of the sound effect in the SFX folder.
The StaticDefs file contains a bunch of the games built-in details (like the names and sorting of stock ships for quickbattle, the stock planetary systems, and the stock sound files). It is a useful file to edit if you don't want to make custom ship, system, and sound files for modded entries.