Several things I can tell you is when the US Mint changed the design of the half dollar coin from Benjamin Franklin to John F. Kennedy in 1964; 5 days after the assassination of JFK. The following year, 1965 the composition of those coins was changed, by reducing the silver content and making it as a clad coin, one metal on the outside of another metal.
The composition of the
Kennedy halves from 1965 - 1970 had a compostion of: Outer Layer: 80% silver 20% copper; Inner Layer 20.9% silver 79.1% copper. Total silver content 4.60 grams, which converts to 0.1479 troy ounce.
1970 was the last year silver was used for production of
Kennedy halves. In 1971, the composition was 75% copper, 25% nickel.
Silver is used on current
Kennedy halves in proof coins only, which can be found in US Mint Silver Proof Sets.