Here is why he was practicing, they were setting up the shot. There was extra light coming in on the shot and things had to be adjusted. Even moving an inch means things are in focus or out of focus. Each shot has to be set up. The Armor was outside the building and the shot, because of covid restrictions. The AD took the firearms from outside into the scene. Also they left the firearms for lunch then came back, they should have been reinspected.
New details have emerged regarding the on-set incident in which Alec Baldwin fired a prop gun on the set of the movie "Rust" that resulted in the death of the film’s director of photography, Halyna Hutchins.
According to a search warrant executed by the Santa Fe County Sheriff's office, obtained by Fox News, the actor and crew were setting up a shot that required Baldwin to cross-draw a revolver and point the weapon at the camera. However, thanks to a shadow that was coming into the church structure from light outside, the camera had to be adjusted to a different angle. Baldwin was working with the director and the cinematographer demonstrating how he was going to draw his revolver from its holster and where his arm would be for the new shot. While demonstrating, the firearm went off.
Director Joel Souza explained that he heard "what sounded like a whip and then a loud pop," and noticed Hutchins, who was standing in front of him at the time, grab her midsection as she stumbled backward. She "was assisted to the ground" by other crew members and camera operator Reid Russell recalls Hutchins saying she could not feel her legs.
Hutchins was immediately attended to by on-site medics and later airlifted to the University of New Mexico Hospital in Albuquerque, New Mexico, where she was eventually pronounced dead. Souza, who was also injured in the incident, was taken by ambulance to Christus St. Vincent Hospital in Santa Fe where he was treated for a wound near his right shoulder
Souza said three people were handling the gun for the scene. Armorer Hanna Gutierrez Reed reportedly handled prop guns left on a cart outside the structure they were shooting in due to coronavirus restrictions. Assistant director Dave Halls handed one of those guns to Baldwin. According to a Santa Fe court, Halls announced that it was a "cold gun" before giving it to the actor, lingo meaning that the firearm was unloaded. As a result, Baldwin and the two people who were wounded believed the firearm was safe to use in the staging of the scene. Both the director and Russell noted that cameras were not rolling at the time as they were still setting up the shots.
Souza said in the warrant that the cast and crew prepared the scene before lunch and then had their meal away from the shooting location around 12:30 p.m. He was not sure if the gun was checked again when everyone returned from lunch. However, he stated that firearms are supposed to be checked by the armorer followed by the assistant director before handing them to the actor. He said he was not sure if people were checked for live ammunition on their person, but stated that live ammunition should not have been anywhere near the scene.