If it hasn't already been said, some support for Alec Baldwin as we know

[Random Boomer]

107. Nonsense. The blame can definitely be fixed.

The direct responsibility lies with the Head Armourer. That is there job: to ensure the appropriate weapon is used and that everyone on the set knows exactly what it is, such "cold" or "hot".

The backup on that responsibility is the 1st AD. They double-check what the armorer has provided them, and they also make sure everyone on set is aware of the presence of a hot/cold gun.

Negligence and/or incompetence in both those positions is necessary for such a tragedy to occur. No one else on set bears that responsibility; it's not their job.

Secondary responsibility lies with the director/production company if they hired an armourer without sufficient training and experience, and same for the 1st AD.

That's the trail of responsible parties, not the actor who was handed a weapon. It's not the actor's job to double-check or second guess or do anything other than hit their mark and play their scene as directed.