Not to say that journalists typically don’t know jack about firearms, but could you tell me what’s wrong with that statement?
They don't have casings. They optionally have jackets. Those are bonded to the bullet. They don't fly off, they remain bonded to the bullet.
Cartridges include the case, bullet, primer and powder. They can fly out of the chamber when ejected.
'Cartridge casings flying' would be correct, or just 'casings flying'.
But 'bullet casings flying' is just an arrogant display of ignorance that the press seems to cultivate about this and many other technical topics.
/johnny
Hmmm... bullets don’t have casings; cartridges do? Quibbling, I guess.