I don’t think that rock salt loaded shells are even available anymore. I have never seen any for sale.
Not directed at you but in general:
That being said, blanks kill. Wadding without any shot, kills. Firearms, like Joe Biden firing his shotgun in the air off his deck, are not warning tools, IMHO.
They were never commercially available to my knowledge as they don’t work
Inside 7-10 feet they might hurt someone but beyond that its just a noisemaker