I have been present when a "Simulated" shootout took place.
The cast 'Sheriff' was the armorer.
He lined up the entire armed cast, and facing them, the entire unarmed cast.
My son and I were behind the unarmed cast, and saw all the prep completely.
The armorer drew his revolver, swung out the cylinder, and showed first the armed cast, individually, that it contained inserts that prevented non blanks from being loaded, then turned to the unarmed cast, and showed each of them the same. I could clearly see the inserts.
Then the armorer repeated this with each of the revolvers of the entire armed cast.
Everyone present had personally verified that the conditions on the set were safe from a live round being loaded in any firearm present.
That is the LAST step that should take place, every time. The first step took place prior to the revolvers being transported to the set, the armorer inspected each revolver after removing it from the safe, to be sure that all still had the inserts from the last use.
The armorer handed each revolver to an individual cast member, and and each of the armed cast personally inspected their assigned gun before holstering it.
Thus, every gun was inspected 3 times before blanks were issued at the scene of the gunfight.
The armorer counted out 6 blanks, said they were blanks, and the armed member of the cast announced, "6 blanks", and inserted them.
At the end of the gunfight, the Sherriff/Armorer lined up the armed cast, and verified that all cartridges were removed from the revolvers, sorted into fired and unfired, and placed in the correct boxes.
No blank ammunition left the set in a firearm. Period.
This on set procedure was repeated at each set, or separate time, even after a coffee break.
All this safety verification was on a very low budget, non union company.
Obviously, in the low budget, fast moving, and stressful filming location where Baldwin was, he did not do his part, the armorer did not do her part, and the cast/staff on site did not do their part. A lot of carelessness and shortcuts by everyone present was required to have this happen.
Further, why was there even a live round present? A projectile that passed through one person's shoulder, and into another shoulder, is not a blank, or even the wrong version of a blank.
edited to add:
Lon Stratton clearly documents that what I observed is close to the industry standard.