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In article , "Newshound" wrote:
I'd guess the heavy one is one of the tungsten alloys used for weights, some
of these are quite hard. Pure uranium is quite soft as I recall (although
perhaps DU is alloyed to make it harder).

I second this guess. They make "easy to machine" alloys with copper that
are still VERY hard. One company that made tungsten alloys was Kulite,
but apparently they sold that business off to H.C. Starck.

Doug White