The Multicannon is a general purpose weapon with three different modes.
Yellow is semi auto.
Orange is full auto
Red is overheated. You can manually overheat or it will automatically overheat if you fire too much in full auto mode.
RMB toggles a zoom if you're in semi auto mode (yellow).
RMB manually overheats If you're in full auto mode (orange).
- The same key used to select the weapon will toggle between the two modes (so if you have it equipped in slot 2, 2 will toggle the modes)
(guides for this item will be linked here)