When we were kids we used to pour coarse pretzel salt down the barrel of our Daisy 105's and let the war games begin. Paintball wasn't even a
thought back then but the salt worked great.
Shotguns and their ammo are rather versatile as long you keep it simple and safe. In the same set of videos from this guy he experiments with a
variety of other improvised slugs as well. His channel is worth checking out if only for pure entertainment.
I bought a bunch of these Bucky balls and as much fun as they
are to have on my desk, I have always wondered what they would do loaded in a 12 gauge shell.
They are really strong magnets, with a good 2 inch attractive distance.