I know when modding the enforcer to fire multiple rounds per shot the sound effect would cascade far longer than normal. It felt like the engine would only evaluate it during certain ticks / windows (polling).
Check out this thread too:
https://saintsrowmods.com/forum/threads/cant-change-weapon-sound.4692/#post-40764
I'm not sure looking at Red Factions files is a good idea when helping someone trying to mod SR4, since in this case, weapons.xtbl doesn't have those fire sound elements and that flag.
If you feel like posting the files for me, I wouldn't mind looking through them. Please include tweak_table.xtbl, effects.xtbl, *foley*, explosions.xtbl (or similar), and any files referencing the original name of the weapon as well, for instance (From Red Faction Guerrilla): weapons.xtbl, and weap_edfpistol.xtbl.
The sounds can be defined in the weapon, an attached effect, or event such as a collision (vehicle), foley, or generic settings like the tweak table.
The enforcer's multishot issue for instance was defined in explosions.xtbl.
You may also be able to define an entirely new weapon, and just clip out the parts you don't want, or only add the parts that you need for testing. RFG had the 'UNIQUE_ID' field that you could just increment to avoid stepping on the game engine. I assume the SRx does as well.