I go through a few boxes of halves each week looking for silver. Last night I come across a 96d half that when dropped, makes no ting, no ping, no sound at all when dropped other than a little thud like a piece of lead would make (poor analogue I'm sure). It does not look counterfeit to my untrained eye and I really don't think it is...but... it has a nice luster to it, the edges are nice and coppery like they should be but it sure sounds like it is made of a different metal IMHO. I don't know what to make of it at all. Does anyone have any ideas regarding what this could be?
If the planchet is internally flawed (such as a large internal lamination) the result can be what is called a dumb planchet that will not "ring" and will produced a Thud when struck.
Another possibility is the coin was heated. I am not a metalurgist (but I did have a metalurgy course in college a few decades ago) but somehow when a coin is heated to a high enough temperature (but less than the melting point) the structure of the metal crystals changes and the coin can lose its ring.
