[user104658]

Originally Posted by Livia

Firing blanks is dangerous. You still have the case and the gunpowder so you still get an explosion so there’s a realistic flash, but anything in the barrel is fired out at velocity, maybe a piece of the case or something that’s entered the barrel accidentally. It’s a risky business. Films like this have armourers to look after the guns so for one not to have been checked or a real bullet slipping through seems unlikely to me. In any case, it’s a bloody tragedy. Can’t imagine how Alec Baldwin feels right now.

Yeah, it reminds me of Brandon Lee's death. They used a deactivated bullet in a previous take (bullet, primer, no gunpowder) and the primer was enough to dislodge the bullet from the case but obviously not fire it - it was sitting half way down the barrel. They then switched to blanks for the next take, without anyone noticing the deactivated bullet had separated, and firing a blank with a bullet lodged in the barrel is basically exactly the same as firing a live round (it's how a musket works for example).

That's why I assumed similar happened here but Sheriff is right in pointing out that this explanation makes it strange that TWO people were shot. I suppose it's possible it hit one and then the other if they were stood together? More info will come, I'm sure.