what 50 cent pieces are 40 silver

[JourneyFitz]

Based on the provided search information, the 50-cent pieces that contain 40% silver are the John F. Kennedy (JFK) half dollars. The context explicitly refers to a "JFK Complete Circulating 40% Silver Half Dollar Collection," which directly identifies this specific coin series.

To elaborate, the Kennedy half dollars minted for circulation between the years 1965 and 1970 are the ones composed of 40% silver. This specific date range is important for collectors and investors. The composition of the Kennedy half dollar changed from 90% silver in 1964 to the 40% silver clad version for these years. After 1970, the United States Mint removed silver from circulating half dollars entirely, switching to a copper-nickel clad composition.