Pollock 187 combines Judd 160 and 161.
Judd 160 and Judd 161 are from identical dies, struck in copper and bronze, respectively.
Judd (1982) diffrentiates the two by weight: 100 grains for the copper; 96 grains for the bronze. However, Pollock (1994), lists a range of weights from 90.9 to 100 grains, plus two additional pieces with weights of 113.4 and 113.9 grains, presuming that the two heaviest weight pieces were restrikes.
PCGS recommends non-destructive analysis to determine the actual composition, because it is impossible to differentiate between copper and bronze by sight.
Sources and/or recommended reading:
Judd, M.D., J. Hewitt. United States Pattern, Experimental and Trial Pieces, 7th edition. Racine, WI: Western Publishing Co., 1982
Pollock III, Andrew W. United States Patterns and Related Issues. Woldeboro, NH: Bowers & Merena Galleries, Inc., 1994