what would you shoot out of a slingshot?

Steel slingshot ammo is the same as big BBs, as far as I know, and that's what I'd use.

For a while I was using a slingshot to harass the geese that park their filthy selves in the pond behind my house. They ARE protected by law, so unfortunately I can't kill them. But I was looking for something to shoot at them that would annoy them, and that I wouldn't have to clean up out of the yard afterward. I settled on jellybeans - small enough to shoot, large enough not to penetrate, and biodegradable.

I grew up killing with a wrist rocket.Even saw a biker dropped with a Pachinco ball.You get hunting shot by the 10lb. bag. #2 works the best when you put 3 in the pouch. Gives you a pattern! Buck- shot works with heavy duty bands. Triple-buck works on cats,best when the shooter is in an elevated position.It was the cheapest way to go a few years ago. I've been dropping tweety birds since I was 5 and I still do.I have to run feeders or I don't get any shots these days.

What I do for sling shot ammo is, when I'm making jig heads for fishing, I'll pour up some round ones in various sizes, without the hooks. It's fairly cheap, and I have a supply on hand from 1/16th oz. to 1/2 oz.

Slingshot projectiles are best, since that is what they are made for. Heavy ball bearings would work too, I'm sure. Rocks if they are heavy enough. Pellets and BBs wouldn't work too good, since they are small and don't have as much energy behind them as the gun would give them.

I have found single ought buck shot to be very effective as slingshot ammo

Glass marbles are easy to find,cheap and work great.

well you might want to get ball bearing from your local hardware store perhaps in 1/4 inch