There are two known specimens and both are fairly nice Uncs. One specimen is Ex-Bushnell-Parmelee-Brand-Dr.Judd, and the other is in the Smithsonian.
This delicate design type is extremely rare and is represented by only two examples in Copper. The reverse features a border of 87 tiny stars (apart from the 1794 "Starred Reverse" Cent, this is the only time such a border was used on an American coin). The example from the National Numismatic Collection was used to illustrate the type in Judd's Pattern book. A second example (ex Bushnell - Parmelee - Brand - Dr. Judd) is said to have a "shattered" reverse die, although no breaks are visible on the coin illustrated in Breen.
Four trial pieces were struck in white metal (Judd 13). Unique, uniface examples exist in white metal of both the obverse and the reverse.
Sources and/or recommended reading:
"United States Pattern, Experimental and Trial Pieces" by J. Hewitt Judd, M.D.
"Walter Breen's Complete Encyclopedia of United States and Colonial Coins" by Walter Breen
"The U.S. Mint and Coinage" by Don Taxay