When I do training, we always start off using live rounds on targets. Afterwards, all live rounds are locked away. Every person then has to physically check themselves and make a declaration they have no live rounds on their person. Then we move on to simmunition training involving paint bullets in special coloured handguns. The instructors check and load and check the magazines with the paint bullets, before handing to participants. With simmunition, if the scenario calls for it, you shoot the role player and they wind up with paint on their special protective clothing.
My point is, someone is always responsible for loading a magazine and someone responsible for loading that into the handgun. Done responsibly and safely, there are no problems.
What I cannot fathom, is firearms firing blanks, or cap guns, or pop guns, or whatever, have been used safely and successfully with zero casualties (except Brandon Lee) in literally thousands and thousands and thousands of different movies and tv shows, the past hundred years? What the hell was so special or different, about what they were doing in this movie?
A movie or tv set should be safer than simmunition, because they don't even use paint bullets. It's all just actors acting, and guns that make a bang noise, if that. In fact it should be as safe as filming a script which requires no firearms.