Naval Copper Rum Pitchers

These all copper measure pitchers were used to measure the daily ration of rum given to the crew aboard naval ships. These pitchers each have a lead stamp on the inside rim showing the government inspection mark and royal cipher which proofed each pitcher to meet volume specifications. They range from one Gallon to 1/8 Gill and have a lead seal with a crest inside.

I can't find any information on the lead stamp that is on my set. Does anoyone know anything about these and what my set may be worth? Thanks!

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