In my pirate campaign, guns are used along side medieval weapons and are used like any ranged weapon. Abilities/feats that affect ranged weapons, affect guns. Abilities/spells/feats that affect arrows, also affect bullets. Guns do more damage than ordinary ranged weapons, but the trade off is a long reload time, limited range and a possibility for dangerous mishaps on a 1. Also, some spells can render you completely invulnerable to bullets, as can also be done against other projectiles. Yes, you can carry a dozen preloaded pistols that you fire in a row without reloading. That is after all how real pirates fought.