There are JABOs with metal - the "Lawnchair" marbles for instance, and rare marbles from the Peltier Mansion Investor Run actually have silver in them. There are also some Alleys, Champions, Peltiers and others that have real metal in them but their numbers are limited and it seems like more of a fluke (somebody tossed a coin or a beer can into the furnace) than an intentional addition of metal.