The regular dies trial piece struck in nickel. These were either deliberately struck for sale to collectors or are mint errors struck on 3 cent nickel planchets.
Pollock enumerates 4 different examples, one of which, the Mike Byers coin, is the illustrated example and current Judd plate coin, has been authenticated and certified by NGC as a MINT ERROR. It was struck on a 3 Cent Nickel planchet and graded Mint State 66 as shown below.
It has since been offered in Heritage 4/15 sale, the again in StacksBowers 5/16 sale now as J542/P607 where it was grade PCGS66. Another is ex Simpson-Heritage 11/20 - PCGS67. A third is in the Durham Museum ex Byron Reed and the 4th is in the T.R. Walsh collection.
It is unclear, at this time, what the true status of these pieces really is.
Photos courtesy of Mike Byers.