Amongst the ranks of rare and valuable Kennedy half dollars is one that by all rights, should technically not even exist. But enough of them have been discovered, and even in pocket change, that you really should be on the lookout for one. That is not to say that they are significantly abundant, but they do exist and will sell for very attractive premiums.
The coin in question is the 1977 Denver mint silver Kennedy half dollar. Now you can look in your red book and you won't find a listing for a 1977 silver dollar of any description, that is because – as I said, the coin is technically not supposed to exist and is classified as a wrong planchet error coin.
During 1976 the nation celebrated its bi-centennial, and to commemorate the event three special coin designs were minted. The quarter, the half and the large dollar each received a special circulating commemorative design. These coins were minted for general circulation and included in proof and mint sets for both 1975 and 1976.
In addition to this there was also a special three piece silver clad set produced at the San Fransisco Mint where the three commemorative coins were struck from a 40% silver or silver clad composition similar to that of the 1965 to 1970 50c coins.
Then in 1977 the regular heraldic eagle design was resumed and things returned to normal for the half dollar. However through some fluke of happenstance a number of the special 40% silver planchets ended up at the Denver mint, where they were mixed in with the ordinary nickel coins and struck as 1977 halves like the one you see here.
So, your next question might very reasonably be – well, how can you tell the difference between the silver and the clad coins?
The simplest way is to check the edge of the coin as a normal clad piece will show a clear copper band, whereas a silver or even these 40% silver coins will not have the same effect.
The only surefire way that you can readily test the coin though is to simply weigh it. A normal Kennedy half dollar is expected to have a weight of 11.34 grams while a 40% silver coins should have a weight of 11.50 grams.
Because this is technically an error coin they are today extremely sought after and fetch sometimes fantastical premiums. During April of 2018 one such coin, graded by NGC with a grade of AU58 was sold at auction for $6 600.