Not everyone can cast spells. it takes a decade-long education to be a wizard. Even in eberron, learning to cast a little utility-magic is like going to tech school.
But guns can be mass-produced, and anyone can use them with a little training. or no training. But yes, special alchemical ammo would be cool.
The idea is that the single-shot pistol would deal like 2d6 baseline, take a standard action to re-load, and have the high-crit property, 30 ft range increment, and be a martial weapon, and be kind of expensive.
With special ammo like bullets that, when fired, spontaneously convert their mass into fire energy, or pressurized acid or something. With super-special single bullets existing that do absurd things. Plus, maybe guns could count as Warlock or wizard implements, allowing them to channel Eldrich Blast through the gun, thus making a badass pirate gunmage.
Maybe that would require a feat.
P: arcane power source
You may use guns as an implement for your class, applying the gun's enhancement bonus to your attack rolls.
P: Gunmage, arcane power source
When using a gun as an implement with arcane powers, you may use the gun's damage dice in place of the power's.