huh, I missed that one, I was looking for live rounds, there are a few other instances involving blanks or prop guns:

The Girl of the Golden West (1915). Actor House Peters Sr. suffered serious burns to his face and hands when a prop pistol exploded upon being fired.

The General (1926). During filming of the epic comedy in Oregon, there were a number of incidents. Several National Guardsmen, employed as extras for the Civil War battle scenes, were injured by mishaps caused by misfired muskets or explosions. Director and star Buster Keaton was knocked unconscious when he stood too close to a cannon firing. Assistant director Harry Barnes was accidentally hit in the face by a blank charge. Train brakeman Fred Lowry sued the production for US$2,900 after his foot was crushed when it was run over by a locomotive wheel during filming of one of the railway scenes

Die Hard (1988). Bruce Willis lost two-thirds of his hearing in his left ear after firing a gun loaded with extra-loud blanks from underneath a table.

there was also:

My Life for Ireland (1941). An anti-British propaganda film made by Nazi Germany. During the epic final-battle scene set during the Irish Civil War, several extras were killed when one of them stepped on a live land mine. The footage is said to have been included in the release prints, although no proof of this has been established

but that’s more of a where did you get a live land mine issue.