Yeah, there aren’t enough details to say.
It’s been relatively well covered already in this thread, but there are a number of different firearm scenarios on sets and how those specific firearms/prop firearms are used varies and it’s difficult without any further information to know what happened.
IN the famous Jon-Erik Hexum case, he had a close-up scene with a real .44 Magnum hand gun, loaded with a blank round. A blank round has gunpowder in it, it will produce recoil, muzzle flash, and a sound similar to a real firearm. It does not have a lead round so if you aim it at someone 30’ away, the projectile in normal operation cannot hurt them. But it may have wadding or etc in the round that will be expelled, at close range the force from the detonation of the gunpowder itself can still make that wadding dangerous. Hexum emptied the gun of all but one round and was “playing” Russian Roulette with it, when it fired the one round he still had, the contents of the cartridge slammed into his skull with such force it fractured and pressed parts of his skull into his brain, he suffered brain death and a number of his organs were donated to people who needed donor organs.
Brandon Lee’s situation was much worse because unlike Hexum Lee was not doing something stupid on set. In Brandon Lee’s case a .44 Magnum revolver was involved in a scene with him that ultimately culminates in him getting shot. An earlier scene, the revolve was loaded with what are called “dummy rounds”–these are supposed to be entirely inert rounds, but LOOK 100% real. These are used in situations where the appearance of the round is important, but there is no need to fire the round or make it look like it’s a real round when fired. However in Brandon’s case the primer was left on the dummy round, which was enough, when the gun was accidentally fired, to propel the dummy round forward into the barrel, where it was lodged.
Now…the dummy round is supposed to look real but be inert (i.e. have no gunpowder), that means the dummy round may basically be a real round i.e. it has a lead projectile in it etc.
For the next scene involving this gun, blank rounds were needed for actually “firing” the gun, again, the blank round essentially has no projectile (or it has paper/wood wadding that does not travel very far), but it does have real gunpowder–a blank round when fired will cause recoil, muzzle flash, and it is propelled violently out of the barrel, just with no bullet in the cartridge, so aerodynamic effects will render it harmless in a relatively short distance. When the actor pulled the trigger to fire the blank, the real gunpowder was ignited and expelled the contents of the blank cartridge out the barrel–they slammed into the previously stuck dummy round, which functionally is a “real bullet” at this point, and projected it out of the barrel with a force maybe not quite the same as a properly loaded and functioning real round, but damn near it. It ripped into Brandon’s body just like an actual “normal” cartridge with a lead bullet in it would, and killed him.