Thanks for the additional information - all help has been very much appreciated.

The coins were measured without the cases, so they certainly don't match the weights given. Comparing them to the images shown over at the Silver Strikers club certainly helped confirm my suspicions as well.

Thankfully, the seller has refunded an amount that means I have paid a price much more comparable to their worth.

Cheers to all for providing insight and information, it's been a great help.