Although described as a regular dies trial piece in aluminum, these were actually deliberately struck for sale to collectors as part of complete sets.
Examples were struck as follows:
Nickel J1260A/P1401 struck on a broad planchet slightly overweight 32.4 grain planchet ex Simpson-Heritage 4/21 - PCGS65, reslabbed now as a broadstruck Mint error as opposed to being a deliberate die trial as unlike the next 2 which were struck from proof dies, it is a business strike and the broad rims appear uneven all the way around. The illustration is from PCGS although the coin is no longer imaged on the pcgs.com/coinfacts website. For more on this piece, click here.
Copper J1260/P1402 with fewer than a half dozen believed to exist.
Aluminum J1261/P1403 with only 2 or 3 believed to exist.
Photo courtesy of Heritage.