There are dots between the N : and DO on them. I'm not seeing the dots. Yours is similar however. AN.DOM translates into "the year of our Lord". They were made for numerous years, PLUS there are variations, PLUS it could be a contemporary counterfeit (kinda doubt it) but that would be cool. Since they were made for numerous years, I would try to find a reference on the varieties. I think there lies your answer.
Hammered silver coins in the US are not common, that's for sure, even the Spanish Maravedis (bronze) are hard to find.