“Look out everybody, things are about to get awesome!”
Known Alternative Fire modes
Atlas weapons shoot a tracking round. After applying it, all regular shots will target the tracked enemy. Known tracking rounds include the standard tracking dart and tracker grenades that explode into hundreds of darts, applying the tracking effect within a small radius. There is only one tracking round per magazine.
Dahl weapons switch between two different firing modes. The options include fully automatic, semi-automatic and burst fire. This switch can also change other characteristics like adding/removing a scope.
Maliwan weapons can switch between two different Elemental Damage types.
Torgue weapons switch between their regular explosive projectiles and sticky explosives. Once stuck, these sticky bombs will explode all at once when the weapon is reloaded, doing more damage than regular shots.
Vladof weapons have various underbarrel attachments that offer a different way of dealing damage. Switching between those is - at least on larger weapons like rifles - represented by rotating the barrel so that the currently active option is on top. If both regular barrel and attachment are minigun barrels they will instead rotate by 90°, activating them both.