In 1963 small coins began to vanish from circulation at an alarming rate. The mint blamed this on coin collectors, and began a series of changes that violated common sense. Like they had done in 1942 they looked for replacements for silver in dimes and quarters. After much searching they decided to change the composition to a clad a sandwich made of copper and cupro-nickel (a copper nickel alloy). They deleted all mintmarks from US coins made between 1964-1967. All of which caused hoarding of pre-1964 coins

The real cause of the shortage was the fact most coins spent 28 to 30 days each month in vending machines, parking meters, and phone booths. A fact documented by noted author Walter Breen at the time. This is another example of the love hate relationship the mint has had with collectors (see coins you cannot legally own)