These coins are a copper-nickel composition, being a nickel jacket over a copper core.
Anything after 1970 contains no silver, with the exception of errors listed below. This was only the second year that the US Mint issued Kennedy Half Dollars in a non silver state. If no mint mark is present it is a P and was minted in Philadelphia. The mint mark for the 1972 Kennedy Half Dollar is on the Obverse/Front.
