If I were to assign percentages here I'd say that someone trying to drill out a bar and fill it with tungsten would be up near 100%. I'm sure the idea has occurred to lots of people independently.

Gold Bar Discovered Filled With Tungsten, How Widespread is Counterfeiting Commodities / Gold and Silver 2012 Mar 26, 2012 - 03:47 AM GMT. By: LewRockwell Robert Wenzel writes: Australian bullion ...

Earlier, we reported on how gold-plated tungsten bars found their way to New York City's Diamond District. While the production of such bars seems sophisticated, the bars are evidently not ...