If you have not checked it out already Superdemonboy15 has a weapon sound replacer in the public mods section. It is what I am currently using and he did a great job.
Otherwise there is realistic gunshots, these sounds are really great also but can be quite loud.
http://www.nexusmods.com/newvegas/mods/35284/?
I would recommend either of these, both are high quality mods and make shooting up the wasteland that much sweeter.