The cone effect is a good idea, but 30 feet is a bit much, maybe 20 feet
and what I would do is add a new weapon type (Simple, Martial, Exotic, and Firearms)
but instead of needing a feet for each, you just take "Firearm proficeny" and can use them all
rapid reload would work for firearms aswell
I use the critical fumble deck, but since firearms are different than most weapons, I can add 52 possibilites (this is gonna be ALOT of thinking)
and damage?
probably more than 2d6 or 3d6
possibly 2d12
sounds like alot, I know, but firearms are more deadly than crossbows and arrows (if you have the great crossbow option, it does a d12, you need to be more powerful than that)
and maybe 2 firing types?
one with a cone (20ft cone, reflex = your normal attack, that way it doesnt become inferior at high levels)
and one that shoots multiple shots, each with an attack, but each attack must be within a 20ft cone (do you want to slaughter a group or slaughter a specific group?)
and you cannot make a firearm magical, only parts (a firing pin of speed, a bayonet of defense, +1 slugs, ect. ect.) because nothing would be as powerful as a +5 keen, flaming, speed musket, it just wouldnt be fair!)
so yeah...you like?