Gun was fired with real rounds, unnoticed a squib round lodged in the barrel on the last shot. Gun was loaded with blanks and given to Brandon Lee's 'attacker' to film the scene. 'Attacker' bursts into room and fires a blank at Lee, but the blank has enough pressure to send the bullet out of the barrel at lethal speed, striking Lee. This is just plain weird, and except for the person firing the squib and not noticing, what could have been done to prevent it?
How to prevent that? Given the number of movies/TV production companies, there are a number of weapon masters companies whose sole business is providing weapons for use in the industry. They control the weapon from the time it's uncased to recased, including the ammo.
In the Lee accident, there are competing stories. The story goes that the prop crew did not have dummy rounds for the close-up scene shot before the fatal one, so they pulled the bullets from live rounds, dumped the powder and reseated the bullets to show what looked to be a loaded gun in the close-up. Another version of that story states a crew member sawed off a bullet tip and placed it in the barrel for the close-up. In that close-up scene, the .44 Magnum was fired, with the resultant squib lodged in the barrel. In the following scene (some hours after the close-up scene) the revolver was reloaded with blanks and was fired, with fatal results. There is a competing story which cites the use of a squib (small explosive) in a grocery bag Lee was holding during the scene. As the scene went, revolver was fired, Lee detonated the squib in the grocery bag to simulate the bullet striking the bag. That squib explosive somehow killed him.
Lee's autopsy cites "GSW of abdomen" as the probable cause of death, but notes Lee exsangunated (bled out) 12.5 hours after being shot.
There were other factors involved, included filming conducted in limited lighting; filming conducted after midnight, including scenes shot outdoors in subfreezing temperatures; no weapon master on set; live rounds present on set; Lee was not wearing a bulletproof vest, which is commonly used when actors are in close proximity to weapons fired on set.
The negligence lawsuit was settled out of court in October 1993, seven months after the accident. While terms were not released, the film production company was separately fined $84K by the North Carolina OSHA, which stated the incident as "the worst kind of negligence." A fairly good article is at
The Brief Life and Unnecessary Death of Brandon Lee