The 1869 Judd-770 is a $2.50 struck in aluminum from dies used on regular issue coins. The purpose of this coin was not to test the dies or a new design, rather the coins were made expressly for sale to collectors. It appears that the coins were sold as part of complete denomination sets (David Akers offered a complete set of six 1869 gilt aluminum denominations as a single lot in Auction '90). Some of the coins may have been sold individually or they may have been broken out of the complete denomination sets - either way, they are usually sold individually today.
Judd 770 is fairly rare and it is doubtful that more than a dozen were made. The finest example is a PCGS PR67DCAM that is now part of the Simpson Collection.