"Fooling around," "playing around," "rehearsing," "practicing," they're all the same words for Baldwin not aware of his surroundings and not following any proper procedures, regardless of who handed him the gun and what they said about it.
It was a gun, it was placed in his hand, and it was his responsibility to know what state it was in first-hand, and then to take proper precautions while it was in his possession.
Was Baldwin aware that the crew was using the gun during off-hours to shoot it in the desert? He was the producer of the movie, were they lying to him about how the gun was contained when filming was done for the day? Did he know what they were doing and condoned it? Did he know what they were doing and ordered them to stop it? Did he know what they were doing and partook in it himself?
Did the lax attitude towards the guns during the off-time carry over during working hours?
It's not so easy to dismiss Baldwin's culpability simply because the gun was "supposed" to be empty.
-PJ
It's not the actor's fault. And in many cases where a weapon is carefully prepared for filming I can see why they would be forbidden from checking it.
If he was handed the weapon and told it was 'cold' his experience would be not to examine the weapon. It's like an airborne soldier: a rigger packs the chute, and you hope he's done it right.