I found this half dollar sized coin a couple weeks ago, using my X-705 with a 6" concentric coil, on a very trashy house lot.  At first sighting out the hole, I thought it was a half dollar. It is made of white metal.  From what I can gather, these were made available in the late 1940's and early 1950's to fans.  Apparently they are fairly common, however, this is the first one of these I have seen and found.