Prop Gun Shooting. One crewmember dead New Mexico filmset

[funkychinaman]

From CNN:

https://www.cnn.com/2021/10/22/enter...ent/index.html

"A search warrant issued by the Santa Fe County Sheriff's Office and obtained by CNN affiliate KOAT revealed that Baldwin was handed one of three prop guns by assistant director David Halls that were set up in a cart by an armorer.
Halls handed the gun to Baldwin and yelled "cold gun," meaning the gun did not have live rounds, the affidavit states.
The gun fired by Baldwin hit Hutchins in the chest and wounded Souza, who was behind her while rehearsing a scene, in the shoulder. She was pronounced dead at a hospital after being transported by helicopter.
The investigator says in the affidavit that the assistant director did not know the gun had live rounds when he handed the gun to Baldwin."

Why would there ever be live rounds on set at all?