dust devil
Observer
I'm planning on using some copperhead bb's I've got laying around.
This chart recommends 10oz per tire for my size tires, but I'm planning to use 12oz, just to be safe. I've heard a little extra can't hurt.
http://www.innovativebalancing.com/chart.htm
Let us know if you try this. I would expect the noise from 12 ounces of BB's running loose in the wheel to be more than annoying at low speeds, as in trail driving, pulling up to and away from stop lights, and so on. I would also expect that they will peen the paint from the inside of steel wheels.
I doubt they will rust, even if there is moisture inside the tire. Constant contact will keep rust off the inside of the wheel and the BB's as well.