Brandon Lee was not killed by a live round.
In the film shoot preceding the fatal scene, the prop gun (which was a real revolver) was loaded with improperly made dummy rounds, improvised from live cartridges that had the powder charges removed by the special effects crew, so in close-ups the revolver would show normal-looking ammunition. However, the crew neglected to remove the primers from the cartridges, and at some point before the fatal event, one of the rounds had been fired. Although there were no powder charges, the energy from the ignited primer was enough to separate the bullet from the casing and push it part-way into the gun barrel, where it got stuck—a dangerous condition known as a squib load. During the fatal scene, which called for the revolver to be fired at Lee from a distance of 3.6–4.5 meters (12–15 ft), the dummy cartridges were replaced with blank rounds, which contained a powder charge and the primer, but no solid bullet, allowing the gun to be fired with sound and flash effects without the risk of an actual projectile. However, the gun was not properly checked and cleared before the blank was fired, and the dummy bullet previously lodged in the barrel was then propelled forward by the blank's propellant and shot out the muzzle with almost the same force as if the round were live, striking Lee in the abdomen.