Each weapon in Planetside 2 has one or more fire modes available, controlling how the gun fires when the trigger is pulled. On most weapons, which have more than one fire mode, you can switch modes by pressing the Switch Fire Group hotkey (B by default).
Pulling the trigger will fire a single group of bullets. The exact amount fired is based on the gun, with most guns firing bursts of 2 or 3 bullets. If there is not enough ammunition left in the magazine to empty the full burst, pulling the trigger will still fire the remaining bullets.
With some exceptions, notably the TRAP-M1, switching to burst on weapons that default to other firemodes willnot affect accuracy. Variants of default weapons (such as the TRAC-5 Burst) that are limited to burst are more accurate than the weapon they are based on.
Similar to semi-automatic weaponry, one pull of the trigger will fire one bullet. However, there is a brief chamber delay between each shot, varying per weapon, where the bolt is cycled or the handgrip is pumped. Until this animation is finished the gun cannot be fired again, even another weapon is equipped before the action is complete.