The alloys on this variety have never really been studied. See Pollock for a listing of these. It is likely that other alloys exist.
Pollock breaks these up as follows:
Pure nickel J1771/P1986. It is not known if these are truly pure nickel.
Nickel alloy including standard coin nickel and at least 6 varieties of German silver J1770/P1987.
Copper alloy J1771A/P1988 At least 2 are known, the Devonshire piece listed in Pollock which is copper-nickel-iron and was sold in the 1996 ANA sale and the other in the collection of Wayne Wilcox. One of these was offered in Kosoff's 10/57 sale as lot 1091 and was forgotten or missed when the Judd book was being written.
Aluminum J1772/P1989. Pollock lists 4 different alloys.