how do you know if you have a real brasher doubloon?

Answer 1

Have it examined by an expert..

Answer 2

Your chances of having one is very slim. There has been no new ones show up, for a long time. Unless it came from a relative way back, say before the Civil War and he lived in New York, the chances are very slim. I have one that is a 1960's copy made by Bashlow, he was some what of a shady character. He made it from a die made from an original coin. It is only gold colored. I do not have a book that lists the weights of the known pieces, but a coin dealer may have such a book. Before paying to have it authenticated, see a coin dealer or two. Hope I have helped some.