The 1877 half union with the small head obverse struck in copper.
The following 3 examples non-gilt are confirmed:
1) Mitchelson-Connecticut State Library
2) Marks (Bowers and Ruddy, 11/1972), Austin (Bowers and Ruddy, 5/1974); Fairfield (Bowers and Ruddy, 10/1977),Bowers and Ruddy, 7/1981); Auction '82 (Paramount, 8/1982), Queller (Heritage 1/2009), Simpson collection - PCGS67BN, illustrated above courtesy of Saul Teichman.
3) Smithsonian, illustrated below courtesy of the National Numismatic Collection of the Smithsonian Institution.
About a half dozen examples of this design have been gilted including the following.
4) Stacks Auction 87 - cleaned proof, gilt
5) Allenburger-Mehl 3/48, Farouk-Sotheby's, 2/54, Schermerhorn, R Green 7/54 MBS, Sloss, Dr. Jarecki-NERCA 79 ANA, Heritage 9/14, Heritage 9/15 - PCGS63 gilt, with scratch in hair and lint mark in field
6) Rarcoa Auction 79, Kagin 8/83 ANA, ANR 7/05 (not sold), Goldberg 2/06, Simpson, Byers, B/M 8/10 (not sold), Heritage 1/13 - NGC64 gilt
The Byers and B/M 8/10 may be reversed here.
7) Heritage 93 ANA, gilt
8) Peters 73 ANA, gilt
The last 2 could duplicate others as these may have been repeatedly cleaned and regilt.
This design is unique in gold J1548/P1721 and is ex Snowden, Haseltine, Nagy, Woodin and is now in the Smithsonian after a furor erupted over its existence.
The circumstances of the return of this and its companion gold piece J1546/P1719 have been shrouded in mystery but correspondence between Woodin's attorney and the Mint in the John Ford library have shed some new light on the matter, and, at a minimum establish, that the 2 pieces belonged to Col Snowden.
One of these letters from Woodin's attorney to U.S. Attorney Henry W. Wise on June 7, 1910 is shown below courtesy of George Kolbe.
"Col. Snowden, who had originally purchased these coins from the Director of the Mint in Philadelphia by depositing the bullion value and the charge for pattern pieces to save them from being melted down, in the course of negotiations between himself and Dr. Andrew, Director of the Mints, came to an agreement with the latter over all matters in dispute between them, and proposed to Mr. Woodin to repay him the $20,000 he had paid for these pieces, in order that he might carry out his arrangement with Dr. Andrew. Mr. Woodin after numerous visits to Philadelphia and Washington and conference with Dr. Andrew, both there and in this city, decided to accept this offer, returned the 50ís to Col. Snowden, and I thereupon notified Mr. Pratt, as did Mr. Woodin, that the incident was closed, and we requested a letter from your office confirming the same. In view of the trouble and expense to which Mr. Woodin was put to facilitate Dr. Andrew in the adjustment of a very difficult situation, your letter seems a little unfair, in that it would tend to create the appearance of a record some time in the future that Mr. Woodin had been compelled to give up something of which he was improperly in possession."
It appears that Col Snowden either gave them back to the Mint or the Mint confiscated them from him after the deal mentioned above was completed.
An incomplete reverse hub trial P3446 is also known.