Prop gun contained a live round.
"Prop gun" might be a little misleading, because they will use real guns on set. It's kind of baffling that they do, especially after what happened to Brandon Lee while making the Crow, but they do.
Anyway, the union that covers propmasters sent an e-mail to its members saying that a live round was in the prop gun, for some reason. That might seem obvious, but Lee was actually killed when a blank was fired because a bullet, or part of one, was lodged in the barrel of a prop gun. It wasn't a live round. Also, the propmaster on this movie wasn't a union member, so possibly not very experienced?
just a little update, for anyone interested.
https://www.aol.com/entertainment/alec-baldwin-visibly-distraught-photos-142757269.html
That's right, aol entertainment. Old school. They are still around.
"IndieWire reports IATSE Local 44, which covers prop masters, sent an email to its members early on Friday morning saying that the gun used in the scene contained "a live round." The production's propmaster was purportedly not a member of Local 44. Yahoo Entertainment reached out to the group for comment but did not immediately receive a response."