There are just so many things that seemed to have gone wrong so I started making a list (probably not nearly complete):
Real bullets were on set
Real bullets were stored in close proximity to blanks
Dummy gun not used during practice/setup for the recorded take
Armorer not union affiliated
Armorer not fully qualified (by her own admission)
Gun was (apparently) not inspected by the armorer before being used (was she even on set at the time?)
Gun was (apparently) not inspected or inspected incorrectly before being given to Baldwin by the AD
Baldwin did not inspect the gun
Inappropriate use of studio guns during off hours for shooting real ammo
Gun(s) were not properly locked up and stored.
Lack of corrective action from previous safety incidents on set
No safety walkthroughs (speculation so far)
The total number of failures points to a systemic issue which likely puts the blame on more people than those who actually touched the gun.
Also, FWIW I doubt this production ever resumes given the amount of negligence shown so far and the likely legal and liability issues because of that.
"Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety." - Ben Franklin