On a film set, each trade performs their own craft, in concert with the others, and 99% of the time, there is no overlap of jobs performed, or tolerated... The gaffer does electric, the grip sets up lighting, dolly tracks, the rigger does rigging, script supervisor handles dialog, teleprompter inputs the dialog, props person handles props. Armorer supplies weapons, ensures safety. The actor acts. It's not likely that an actor needs to ask "are you sure this weapon is safe" any more than an actor needs to ask the DP "are you sure the focus puller is on it...?" They do their job, you do yours. A tragedy for sure, and someone made a huge mistake.