"These plates are really beautifully formed. Would they have been formed with an English wheel or some other method? Does anyone know for sure?"
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They were often installed by gun workers in India, who, I am sure, didn't have access to sophisticated tools, such as an English wheel. They did have access to a good means of heating steel in a forge like thing, to good old fashioned hammers and anvil, with rounded steel anvil sections, and a lot of sweat and labor, along with skill earned from long term working on such things.