Coin FUN-nel (Funnel) by Royal Magic
Hand the coin funnel out for examination, and allow a spectator to lock a half dollar inside, separating one chamber from the other. There's no way anything can pass through the half dollar. Your spectators are sure of this. The magician then borrows quarters from his skeptical spectators.
One at a time, and with no sleight of hand at all, the borrowed coins penetrate the half dollar.
The moves are easy to do, and can be mastered in a matter of minutes.