Thanks jbuckster!
A re-run and a new one1959 St Lawrence Seaway
Heraldic Art Co Medal No 2 
The 1959 St Lawrence Seaway does come in thin and thick planchets.
I won't know what I have until it arrives.
I already have the thin one.The thin had a reported mintage of 3700
The thick had a reported mintage of 2200
The thick are considerably heavier than the thin.
The mintages figures on this series is not 100% reliable as those of you who know about these so called half dollars have found some are quite scarce despite the numbers given on checklists.
There also could be a factor of survival as many coins and silver medals were melted down in the late 1970's during the big silver boom.
There is an amazing online book found here with a lot of good information.
https://archive.org/details/CONA201...als/mode/2up1970 Charleston Heraldic Art Co Medal 
My second catch today was the 1970 Charleston
This is seen much less often and sometimes will fetch some crazy money.
I think it is more common than those around 1973 to 1978 but much more scarce than the majority of the earlier 1960's. There were 3 different regular issues each year. Sometimes one or two are seen more often than the other for that year.
One occasional Heraldic Art medal was minted in addition for each year from 1961 to 1966 and then none were minted until the Bicentennial 1976 medal.
This makes a total of 67 designs in total, 60 regular and 7 occasional medals for what most would consider a complete set.
I now have 36 of the 67 leaving me 31 to find if, and that's a BIG IF . . . the price is right.
I have three duplicates now because they were inexpensive and I couldn't pass them up.
There are still some I could pick off easily but they just don't grab me.
There are a few variations and perhaps a couple more very rare special minted pieces for Historical society and Coin clubs.
Do not be fooled by restrikes in copper with cancelled die marks and especially copper errors such as off center, double struck or broadstrikes.
They are recent and intentionally made errors by the one who has the cancelled dies. Unaware people are buying them as if they were true minting errors.
