This is a reverse hub trial, in copper, for the 1964 Kennedy half dollar design. It has the "D" mintmark for Denver in 2 different locations, one of which is the correct one and may represent some sort of set-up trial for the mintmark's placement.
It has been defaced with small ball tipped chisel marks and is ex R.B. White, Bowers and Merena 9/89, Bowers and Merena 11/99.
Photo courtesy of Heritage.