The guns firing, especially the Pistol, is quite loud compared to other sounds in the game, and none of the volume options except for master volume have an effect on this. There should be a seperate sound setting for this some where in game (maybe in the mod config), but there doesn't seem to be. Ideally, I'd want the sound volumes to be inline with everything else so I can actually hear zombies and such without jumping every time I've fired the gun for the first time in hours. This also interferes with my ability to watch youtube videos while I play, since most of them are a bit quiter than the game is, even with the sound boost from youtube enhancer turned on.

Setting master volume to 50% seems to be perfect volume for the guns, as they're still loud enough to be louder than most things, but not so loud to be "holy crap" loud and disturb others while I'm playing, but this makes everything else in the game too quiet.

I second this. On the topic of sound, a good number of guns also seem to have the position of the source a little to the left of the player, the revolver and the double barrel shotgun are a few examples.