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.
In addition to the illustrated aluminum example, these were also struck in copper J1369/P1514.
Only 2 or 3 are known in either metal. The 76 ANA, Ivy 4/77 pedigree for one of the copper trials is an error listing which was actually the pedigree for the half eagle trial J1371/P1516.
Photo courtesy of Superior.