If it was a different actors then yes, they should still be held accountable in some way. Anyone who has ever taken even a basic gun safty course knows the first thing you do when you are given a gun is to check the chamber to see if it is loaded every single time.
Every time I go so a shooting range with friends and it is their turn to shoot I place my handgun on the bench unloaded with the chamber/Cylinder open and the mag/rounds next to it. Complacency kills and this movie is a perfect example of extreme negligence from the top down.