This is a restrike, made in the 1870s, using an obverse design originally used on J93-J94/P105-P106 combined with the regular large letter reverse used from 1842-1866.
It is attributed to Gobrecht in the original editions of Judd but a July 12, 1843 letter from W.E. Dubois to Matthew Stickney in the Peabody Essex Museum attributes this design to Kneass as noted below.
"One half dollar of 1839, of a die which you never saw before, nor did I, until today. This die was made by Mr. Kneass, the late engraver, since deceased. A very few pieces were struck; I don't think I could get another, except for the Cabinet, where there is none as yet".
The following are confirmed:
1) Anderson-Dupont, Stacks 11/54, River Oaks-B/R 11/76, Witham-Auction 81, Evan-B/M 8/98, Superior 5/03, Simpson collection - PCGS64, rim mark at NI of United on reverse, illustrated above
2) Stacks 76 ANA, Stacks 11/89, Queller-Heritage 1/09, B/M 2009 ANA, Heritage 2/10, Heritage 8/11 - NGC64
3) Farouk?, Numismatics Ltd, Bass-HWBRF, B/M 5/99, Superior 4/03 - PCGS62
The Dr Judd coin is possibly another.
Was this struck using the same reverse die as J538/P602, the unique 1866 no motto half dollar and/or J243-J244/P299-P300?
These were also struck in copper J98/P108 with the following confirmed:
1) Parmelee, Byron Reed-Durham Museum - ICG64BN
2) Leidman in 1972, Bass-B/M 5/99, Simpson - PCGS64BN
3) Farouk, Dibello-Stacks 5/70, Witham-Auction 81 cleaned & lacquered, Superior 10/92 as PCGS65BN (chocolatized), Queller-Heritage 1/09 - NGC67BN
4) Kreisberg, Heritage 6/87 - graded proof 64BN
5) Legend inventory 12/12, Heritage 1/18 FUN - PCGS64RB
6) Newman-EPNNES, Heritage 4/13 - NGC66RB
One of these is ex Stickney, Brand (journal #38996).
Photo courtesy of PCGS.