Fox News writers used the word inert.
The expert armorer said you have to listen for the SOUND of B.Bs rattling, not to say that there were actual B.Bs inside.
I am not an expert on this so correct where it is wrong.
Please see #23.
The WSJ reported that the prop company that made the dummy rounds inserted a “pellet” into the case where powder would be on a live round, specifically so you could shake the cartridge and tell it was inert. Maybe it was a pellet, maybe a BB. Given the quality of journalism, there’s no way to be sure.
This appears to be done to avoid having to drill a hole in the side of the case which would be a visual cue that would serve the same purpose.