Alright so I pulled a 71 it is not an s mint does not seem like a proof does not have the ring of silver when dropped but does sound different. And has the silver edge. Platted well it is another crapper 11.3 grams
Weigh it. It should weigh in at 11.3 grams, if it weighs 11.5 grams you might have something. In 71 there were some halves that were accidentally minted on silver planchets that were left over from the 1970 stock.