The most basic form of attack with a firearm is a single shot. One attack is one pull of the trigger and fires one bullet at one target.
The Personal Firearms Proficiency feat allows a character to make this sort of attack without penalty. If a character isn’t proficient in personal firearms, he or she takes a –4 penalty on attacks with that type of weapon.
A number of other feats allow a character to deal extra damage when he or she fires more than one bullet as part of a single attack at a single target. (If a character doesn’t have those feats, he or she can still fire more than one bullet—but the extra bullets don’t have any effect, and are just wasted ammunition.)
As with all forms of ranged weapons, attacking with a firearm while within a threatened square provokes an attack of opportunity.
Because of the weapon’s unwieldy shape and size, an attacker using a longarm takes a –4 penalty on attacks against adjacent opponents.
If a ranged weapon has an automatic rate of fire, a character may set it on autofire. Autofire affects an area and everyone in it, not a specific creature. The character targets a 10-foot-by-10-foot area and makes an attack roll; the targeted area has an effective Defense of 10. (If the character does not have the Advanced Firearms Proficiency feat, he or she takes a –4 penalty on the attack roll.) If the attack succeeds, every creature within the affected area must make a Reflex save (DC 15) or take the weapon’s damage. Autofire shoots 10 bullets, and can only be used if the weapon has 10 bullets in it.
Autofire is not the same thing as burst fire, which involves firing a short burst at a specific target. Firing a burst requires the Burst Fire feat. If a character fires a blast of automatic fire at a specific target without the Burst Fire feat, it’s treated as a standard attack. The attack, if successful, only deals normal damage—all the extra ammunition the character fired is wasted.
Some firearms—particularly machine guns—only have autofire settings and can’t normally fire single shots.