I recently found this padlock while metal detecting a site that dates back to the 1750s and also saw Civil War action. As you can see the brass keyhole cover has a crown with two crossed scepters under it. Below that is the word "PATENT."

I would like to know the approximate date of manufacture (year range) as well as any other information that might be provided. Thanks in agvance for your help!Click image for larger version. 

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