By the introduction of the real de vellon by king Jose Napoleon in 1808, 1 real de plata (silver) was indeed worth 2.5 reales de vellon (billon).
As both your coins have the same value: 8 reales de plata = 20 reales de vellon, their intrinsic value is the same. They are both struck in 0.903 silver and they must have the same weight.
Numista (and numismaster) gives 27.07 grams for the 8 reales and 27.08 grams for the 20 reales.
As both your coins have the same value: 8 reales de plata = 20 reales de vellon, their intrinsic value is the same. They are both struck in 0.903 silver and they must have the same weight.
Numista (and numismaster) gives 27.07 grams for the 8 reales and 27.08 grams for the 20 reales.





















