The gunbelts often seen in western movies and TV shows (despite being a rarity in real life during the late 1800s) had cartridge loops containing dummy rounds.
A dummy (inert) round is used specifically when the gun is pointed toward the camera, unless the camera is operated remotely. It allows the viewer to see the bullets in the cylinder, giving it a realistic look.
That also suggests to me it was supposed to be dummy rounds, rather than blanks.
The gunbelts often seen in western movies and TV shows (despite being a rarity in real life during the late 1800s) had cartridge loops containing dummy rounds.