Picked this up from an estate sale years back. I remember it was in cardboard protector with the original mint box bottom and certificate. Protector had ??? mark's written on it but that was it. I purchased it along with a couple other things and just now decided to take a closer look. Weighed it 5X and checked scale with other 50c pieces but weight is 12.57g. I know this was the year mint used 90% silver on this proof but information indicates 11.34g. Any idea's and help would be greatly appreciated.