Hey dude I'd love to see your gun rules. Are they posted anywhere?
Well advanced tech weapons haven't made an appearance yet, but for regular weapons I actually chunks of the idea from someone else, (though I can't remember where I read it).
A lot of it is rather campaign specific too. From a cultural standpoint guns are considered to be semi-magical in nature (they arn't, but that's what people think) and their ownership and use is extremely restricted. It's also a pre-industrial society in most respects. Everything is made by hand, and gunsmiths work in small family clans known as Arsenals, and these are some of the most secretive organizations in the world. They're one part business enterprise, two parts secret society. The techniques they use, particularly the formulas for gunpowder do not leave the family, and they will spend astronomical amounts of money, and spill a metric ton of blood to ensure that their secrets stay safe. The prices I mentioned above are the prices if you're dealing directly with an Arsenal. The catch is that they have an extremely short list of clients that they will deal with. If a PC wants to purchase a gun he's looking at a 200-300% markup.
Ammo doesn't come cheap either. This is mostly because the primary users of guns are reskinned elves who form the ruling class of the society. The whole aversion to base metals thing means that for all intents and purposes bullets are made from starmetal (the campaign equivalent of mithril). Not only is starmetal a lot tougher to work with than lead, but it's worth a small fortune in and of itself.
From a rules standpoint a gun can be fired once a round like any other weapon. Reloading a gun takes a single action whether it is removing a spent cartridge and inserting a new one, or popping in a stripper clip, or changing a magazine. If you are loading individual rounds into a revolver or a tube magazine you can load 1+your agility bonus per round. The exception to this is a muzzle loader. To reload a muzzle loader requires a successful agility test with a DC of 25. Each failure subtracts 5 from the DC the next round. Generally speaking you're looking at 2-4 rounds to reload before you can fire again.
As far as damage goes the big difference is that damage dice explode when maximum damage is rolled. The number, and size of dice varies. Generally speaking higher quality guns will roll a greater number of smaller dice whereas cheaper, 'mass' produced guns would roll fewer large dice.
A muzzle loading percussion cap musket for example which is one of the most common weapons does 1d10 damage. Good for an opening salvo in an encounter, but after that you're falling back to blades. These are popular among elite soldiers, and the personal guards for powerful families. They're expensive weapons, and you need connections to get a large supply of them but they are the closest thing you'll find to 'mass produced' guns.
An officer's carbine though would be breech loading and might roll 2d5 or 2d6 damage depending on its quality. It would use rolled metal cartridges and can be loaded from the breech. A good weapon for someone who spends most of their time in the rear ranks since it can keep up a pretty steady rate of fire.
The same carbine from a master gunsmith, the gunsmithing equivalent of Maramusa might roll 3d4 or 4d3. Some of these might even offer a to hit bonus to represent their effectiveness against armour.
I haven't even started trying to muck about with advanced weapons since the PC's are a long way away from dealing with them yet.