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.
It is unclear, at this time, what the true status of these pieces really is.
Photos courtesy of Mike Byers.