I wonder what the filming SOP is for semi auto firearms? Like will each actor load their own mags with blanks to insure that only a blank is loaded? Since they are the ones who pull the trigger and can be held liable if a real round is loaded.
This is much easier to do with a revolver.
Most reputable gunsmiths on set will have a system to keep all arms and ammo locked up to prevent tampering/accidents.
In the case of ammo, almost all will prohibit live ammo anywhere near the set to avoid the slightest possibility of a live round winding up where it shouldn't.
Furthermore, it's common knowledge that a blank round can injure or kill if it's fired in the right spot on a person at the right (close) range. Blanks use a wadding to keep the load in the cartridge, and that wadding becomes a projectile. Knowing this, many scenes are shot in segments that remove people from in front of the firearm when it's fired out of an abundance of caution.
You can do everything right, and still have an accident. By incorporating safety rules, like never point a gun at anyone/anything you don't intend to destroy, you can avoid catastrophic outcomes when accidents occur.
The people running the production of
Rust were careless, and someone died. There doesn't have to be an SOP to prevent this from happening. Just common sense gun safety rules.