Live round on a movie set??
That had have breached several safety protocols
Absolutely. Even at a glance, a blank round is easy to distinguish from a live round. This is a serious foul-up. I have worked a lot with reenactors, and you can make a dummy round in which the cartridge is filled with sand instead of gunpowder to simulate the weight of a live cartridge. There was no good reason for there to be a live round on location.