Alternate fire

From Styleguide

alternate fire

In games that designate a key or button on the keyboard or controller as a primary fire trigger, a second button or key may be designated as the alternate fire key or button. Alternate fire triggers a secondary function of a weapon or item, such as launching a grenade instead of shooting bullets.

Alt. fire acceptable after first reference.

Example: Instead of buckshot, the alternate fire mode causes the shotgun to spit out a grenade. Press X to activate alt. fire.