Huge Lot of Unsearched U.S. Steel Pennies - This lot is completely unsearched, and could have double die strikes, error coins and extremely rare. They have been in a family's estate. They have been in storage for over 45 years. Due to wartime needs of copper for use in ammunition and other military equipment during World War II, the United States Mint researched various ways to limit dependence and meet conservation goals on copper usage. After trying out several substitutes (ranging from other metals[1] to plastics[2]) to replace the then-standard bronze alloy, the one-cent coin was minted in zinc-coated steel.