I have examined a silver 8 reals from this period before and it was lozenge shaped from being turned and pressed between two round rollers. If it is a regular round, it may have been minted differently or cast up. If it is slightly distorted, then it was either cast off an original or is some sort of off metal strike.
It doesn't really look cast, but you can get some decent detail with a lead-tin-copper alloy if you know what you are doing.