U.S. Coins by Egantx7

Question 5

Older pennies were made largely of copper with small amounts of zinc (and sometimes occasional traces of tin). In the middle of what year (within one year either way) did the US mint shift from making pennies largely of copper to largely zinc, forcing collectors to differentiate pennies of this year by mass (about 3.1 g for copper cents, and about 2.5 g for zinc cents)?

1982 (1981-83)