A fully automatic (or full auto) bb gun constantly sends ammo downrange when the trigger is squeezed and only stops when the trigger is released, CO2 runs out or the ammo magazine is empty. This is slightly different than semi auto bb machine guns which have several fire mode options such as one, three or six shot burst mode with each squeeze of the trigger. You can find airguns that offer full auto, semi auto, or full & semi auto together.