Although these are described as regular die trial pieces in the standard references, it is more likely that the off-metal 'trials' of this year were deliberately struck for sale to collectors as part of complete gold and copper sets of this year containing the with motto half eagle J445-J446/P517-P518, eagle J449-J450/P521-P522 and double eagle J452-J453/P524-P527.
About a dozen are known.
A gold restrike for this year is known, to view click here. It is believed to have been made to complete gold proof sets of this year with the "In God We Trust" pieces mentioned above.
Photo is of the Eric Newman example courtesy of Heritage.