it's happened before
Gunfire in movies appears very convincing because blanks used to imitate live ammo are basically modified real bullets, according to the BBC.
nypost.com
The wadding used to hold the gunpowder in place instead of a bullet gets expelled when the trigger is pulled and can cause serious damage – and even death, as was the case when actor Jon-Erik Hexum was killed in 1984.
Hexum was fooling around on the set of the CBS TV show “Cover Up” during a delay in filming. He loaded a revolver with a blank, spun the chamber, put the gun to his temple and pulled the trigger.
The blank’s wad struck his head, fracturing his skull and sending bone fragments into his brain. He died about a week later.