When I was a kid I’d load sand in the bore of my Daisy pump BB gun, sit on the front porch & shoot flies. Eventually, I worked up to hitting them with BBs instead.
However, the sand didn’t leave dings in the porch boards, so I went back to sand.
Probably the guy doing the salt gun did the same thing as a kid. I would have gotten in beau coup trouble from my dad stuffing gunk down the bore of my bb gun! lol “Make sure the barrel is clear before you fire”.