You are negligent in your thinking. There is failure all down the chain of custody on this, and the person least responsible for this is Alec, who probably knows diddly/squat on gun safety. He's given a prop gun and told...ACTION.
Here, kids, let's review the three primary rules of gun safety (with a 4th added in all by myself. Neener), which I call the firearm-safety pyramid.
I'm a registered MA State Police firearms instructor (And NRA as well, but fuck them, they steal from their membership for personal gains), so don't argue with me, because you will fail.
1. Always keep your firearm pointed in a safe direction.
2. Always keep your firearm unloaded until ready to shoot.
3. Always keep your finger off the trigger until ready to shoot.
Bonus! 3A. Always know what is beyond your target.
The problem started with the armorer, and the pyramid in this setting.
The pyramid is worded the way it is because it is always assumed that one will be handling live ammunition. There is nothing in the pyramid that covers something like a movie set, where there is usually no live ammunition around. So on a movie set, rule#1,2 and 3 are negated because let's face it, pointing a gun at the camera and pulling the trigger for that effect is, well, violating the rules, but is needed for that particular scene. But it is supposed to be with no live ammo.
With live ammo, if the top 3 rules are followed, there will be no injuries. You have to break all three rules to have an injury.
There should have been a single primary rule applied to the armorer, and all those down the line.
1. Assure no live ammunition is in the firearm when it is handed to the actor.
In this case, there is no pyramid, because playing cops and robbers on the TV screen doesn't need a pyramid. Just that one rule.
In firearm safety, when handing a gun to another person, you always assure that the breech is clear and the gun is in a safe mode. The person receiving the gun then checks to assure the gun's condition. (Action open, safety setting, etc.)
But you cannot expect that to be the case on a movie set where so many assumptions are made, and actors may have never handled a firearm before.