The Kennedy Half Dollar series underwent two significant changes during the second decade of issue. The first change was compositional and the second change was the design.
The last 40% silver Kennedy Half Dollars were issued in 1970 and 1976. Notably, neither of these coins were released for circulation. The 1970-D Kennedy Half Dollar was issued only in Mint Sets. The resulting low mintage, granted the coin key date status for many years. The 1976-S was specially minted in 40% silver uncirculated and proof for special 3 coin Mint Sets and Proof Sets. All other coins issued for the series during this time period had a new copper nickel clad composition, which had been in use for the dime and quarter since 1965.
The half dollars from 1976, actually minted in both 1975 and 1976, also featured a different reverse design to mark the Bicentennial of the United States of America. Independence Hall in Philadelphia was picutred on the reverse of the coin. The obverse of the coin carried the dual date “1776-1976”. The regular eagle reverse resumed in the following year.