I have no clue if that coin is real or fake .Getting it over 4 decades ago soon as I pulled it out what a smile I had yesterday.
It is a 1793 Charles IV Mexico 1/2 Real, because of the wear I would say the weight you have is good. it is a genuine coin
You think that circulation wear would account for more than 10% of the weight difference? I refer you to this recent thread where weight loss from circulation wear is discussed.