The regular dies trial piece. It is likely that many of those listed below are mint errors.
Examples are known as follows:
Copper J550. This was delisted by Pollock as being indistinguishable from a regular bronze piece without metallurgical analysis. Examples were included in the double set that was apparently stolen from the Iowa State Historical Museum. As the whole set is missing, it can not be checked to see if they were really copper or regular bronze strikings.
Copper-nickel J551/P613. This may actually be a mint error struck on leftover copper-nickel stock as used from 1857-1864 as one example is a business strike. Only 2 or 3 are believed to exist including one in the famous Lohr collection.
Nickel J552/P614. This may also be a mint error struck on leftover stock used to strike J406-J406A/P475-P476 or on misrolled nickel 5 cent piece stock. Only 3 or 4 are believed to exist including the illustrated example above which is a business strike and not a proof.
Oroide J553/P615. This may be a misdescription of the copper-nickel piece listed above or a golden toned regular issue example. One was in the Farouk sale.
Photo courtesy of American Numismatic Rarities.