So I am working on a gun mod, making level lists and stats and such but I am having an issue. I dont know how to make the gun sound well, less loud. I dont want people to go deaf using the gun mod.

You can either manually make the sounds quiter using audacity and de-amplifying them or in your geck where you make the new sounds entries decrease the static attenutation [dB] level which will make them quiter,just do some trials and errors with the values there and you will find what you need.

When I do voice acting for mods I use Creative WaveStudio (I think you can get it even if you don't have SoundBlaster) and it's got some nice leveling controls too. I haven't used Audacity, but most folks swear by it.

Personally I wouldn't use the audio sliders in the GECK to decrease the dB, because sometimes the GECK doesn't accept/save them and it could still be loud. So I suggest Audacity too, it's fairly easy to use.

I have also used audacity, for exactly this reason. Some of the AK fire was far too loud

Nothing beats Audacity for "Quick and easy" edit IMO.

Totally agree with bl4d3l0r3s.
Voiced a drone for a little personal quest and had the problem of being too loud, editing in audacity all the lines has been mighty fast and easy. From that moment, I always use it for quick editing, in yours/mine cases, simple volume issues, it's the most convenient tool.