Let's say I'm making a mod that adds a custom weapon that fires normally fires a certain projectile when fired normally, and that's 10mm bullets. But if you zoom in with Right Mouse Button and press E, the gun instead shoots Projectile2, a Dragon's Breath Shotgun Round. And each use of this feature costs 10 bullets of 10mm ammo. This is just an example of what the alt-fire mechanic could be used for. How would I go about coding in a feature like that, or if that doesn't work, a "Press K while this custom 10mm gun is equipped to fire Dragon's Breath ammo for free" feature?