Although described as regular dies trial pieces, these were actually deliberately struck for sale to collectors as part of complete off-metal sets.
In aluminum, as illustrated, only 2 or 3 are believed to exist.
An example in copper of J1043 which was delisted by Pollock does exist. The coin has been analyzed by Alan Meghrig and was found to be 99.7% copper, 0.164% aluminum and 0.152% nickel and weighs 92 grains.
Photo is of the former J.E. Drew example.