IIRC there are no spent casings ejected. One of the design difficulties of the Warthog was that the cannon fires so fast the spent casings could rip up the wings if they were ejected. Therefore they are kept inside the weapon system. I may be remembering wrong or things may have changed.
I do know the cannon is powerful enough to stop the Warthog in the sky if the plane is flying slowly enough. I also once saw what a 2 second burst did to a 30 foot pile of sand. I would definately not want to be the enemy of a Warthog.
Shalom.
That gives the air force the chance to save money by "Reloading" the casings.