It's getting rather interesting. There are reports that the movie crew were using the firearms on the set off-hours and just shooting them off in the distance at the ranch where the filming was going on. I get that some people like shooting off guns in the middle of nowhere. So that could explain why there might have been a live round in the gun. Seem really lax that the armorer wouldn't put a stop to that and wouldn't make sure that the guns weren't locked up when not being actively used in filming.
“Working with Hannah, I’m surprised that any of this happened under her watch,” said Crow. “I thought she was an exceptionally young, up-and-coming, very eager and talented armorer. She was without a lot of experience, but coming from her family lineage, I thought she was exceptional, professional, and I thought she had — I still think she has — many years of an amazing career ahead of her.”
Reed grew up on Hollywood sets, often tagging along with her father, a former Marine who served as Brad Pitt’s gun coach on “The Assassination of Jesse James by the Coward Robert Ford” and served as a quick draw expert on “Django Unchained.” She has said that her favorite childhood memory with her dad was visiting the set of the 2007 film “3:10 to Yuma” when she was around 10.
The prop gun used by Alec Baldwin, that killed cinematographer Halyna Hutchins on a New Mexico movie set, had reportedly been used by crew members offsite for 'fun'. The gun, which misfired while Baldwin held it on the set of the movie "Rust", may have even been loaded with live rounds when it was supposed to be used for target practice. Various sources claimed that the gun was even fired at off-the-clock gatherings.