I love that you did this, though I was much happier when I replaced the Buckshot sound with the Slug sound, then replaced the Slug sound with the M30 launching sound. The current Slug sound is too sharp for my tastes, as this is going to be played constantly in an attack chain, so I wanted a duller sound effect to go with it.
On the other hand, using the Slug sound for Buckshot made it sound hefty and impactful, the reload on the end is more amusing on a shottie too.
http://www.virtueverse.net/wiki/Massacre_Melanie -the original Fire/Dark Corruptor -
http://boards.cityofheroes.com/showthread.php?t=115217
The Guide to BURN
Hm....going to check this out. Looks fun.
Thank you for your comments! 
I'm glad that you enjoyed the pack. It's true that the Slug sound is very overbearing, but it's my favorite, and I use that power the most, haha! If someone asks, I'll post a quick guide on how to rename the sounds to suit their tastes.
Sorry it took me so long to get on the boards and post this, I am the guy who requested you post this up in game. I have to say I have been using the sounds and love them, especially the sniper-rifle and slug sounds. I've just gotten used to the new sound completely now Very nice work.
I have no idea if this is the right place to post this, but in any case, here we go.
I've always liked the Assault Rifle powerset, but being something of a firearms enthusiast myself, I simply cannot stand the default sounds for the set. So, a few years ago (quite some time, actually), I created my own set of sounds. All of the sounds in this pack are from freely-distributable sources. Thanks to Virtue:Konohanasakuya for providing me the impetus to actually post this pack!
How to use:
Create a folder in your City of Heroes game directory (typically Program Files\City of Heroes or Program Files (x86)\City of Heroes) called data, so that you have \City of Heroes\data. Extract the .rar file (using the archive extractor of your choice, typically WinRAR or 7-zip) to this "data" folder, maintaining directory structure. If you don't know what that means, don't worry about it; it's usually the default option. This should give you \City of Heroes\data\sound\ogg\weapons\, with some files in it.
How to remove:
Simply delete the "sound" folder, or any of the subfolders. Alternatively, just delete the individual sound files, or if you have no other mods installed, the "data" folder you created.
Sounds included in this pack:
assault3.ogg - Used for the "Burst" power. A meatier sound. Some may feel it's too meaty for the weak "Burst" power. Some may be right. I still love it.
fullauto.ogg - Uses the same base sound as assault3.ogg for consistency. Includes reloading sounds (from an M249 LMG) at the end that are so fast they are a bit silly. I may make another version without them. Also, very loud and long. Might be jarring. I like it, anyway.
grenade2.ogg - While I do like the default grenade sounds, this is a little bit more like grenade launchers I have heard in real life.
grexplo2.ogg - A new grenade explosion effect. Less "distant artillery explosion" and more dynamic.
machgun_single.ogg - The sound effect for "Slug". VERY meaty and quick, like that power. I adore this noise.
sniper1.ogg - The sound effect for Sniper Rifle, the default for which is my most-hated sound in the game. Punchy and powerful, with a very quick bolt-action noise tacked on. Silly, but I enjoy the sound of it. It's familiar.
Anyway, if you like it, tell your friends! I'd love to see this gain popularity. Likewise, if you don't like it, let me know, and I might be driven to create another pack or other sound replacements.
Where to get this file:
Mediafire - http://www.mediafire.com/download.php?0ul4aw8tsaq31rl
Edited to fix the link, as it didn't actually work.
Edited 2011 to fix the link again. It's a .zip file now; anyone modding their game can probably figure out what to do with a .zip file. :P