This coin maybe an example of poor quality control at the mint and possibly a fiddle with the silver content in Mexico
Eight-real coins like this were minted in Spain and its colonies since 1497. The name order real descended of rey, the Spanish word for King. In the 18th century, this coin was the first real world currency. In English, it was called the coin "Piece of Eight" or "Spanish eight", because you the coin could share in the absence of change in eight parts, each to a real, or in four parts to two Reales (hence the name quarter-(Viertel)-dollars).
This coin has broken due to a floor in the silver pouring stage. There are three pieces and all is intact
This would justify the excellent condition of the coin which is kept in a coin case.
Obverse Description: Bust of Spanish Monarch Carolus III facing Right
Obverse Legend: ·CAROLUS·III·DEI·GRATIA·1783
Reverse Description: Crown above Spanish Arms within Shield between support of the Pillars of Gibraltar or Hercules.
Reverse Legend: HISPAN*ET*IND*REX*M* 8R*F*F
Specification: 26.31 g, .896 fine silver,
Product code: Order 1783 Carolus III 8 Reale coin