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.
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.)
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.