it's a 1703 Mexico half real
Brian, what you found is a very nice little (17)03 dated Mexico mint half real, featuring a Philip V monogram... That isn't a "7" after the 3, that's the left edge of the crown... it shows "0 3 * crown" (the * or period being a divider in the design). Part of a shield cob? 1537?... the rare 3 Reales??!!... getting way off the reservation there. One aside about the monograms... it can be hard to attribute one of these Philip monograms. Keep in mind, they used some variant of a "PvS" monogram under Philip II (1556-98), Philip III (1598-1621), Philip IIII (1621-65), and then again for Philip V (1700-1733)... While there are differences/identifying features that someone well-versed on these can attribute them with, the monogram for all the Kings Philip don't look a heck of a lot different from each other. They can be easily confused...
Also, dating on the Mexican pieces started in 1607 for the shield-type 1R, 2R, 4R, 8R... and right around then on the monogrammed half-real as well.
Aside from some old scratches/contact marks, your piece is in very decent shape. What makes it nice is the strike and its positioning. The half real pieces were very hit or miss in terms A) how level the planchet was, which affected how much detail would actually make it onto the coin during striking, and B) the centering of the design during the strike. Ever try to perfectly stamp a thumbnail-sized piece of metal??!! Whenever I see these, I always wonder if doing the half-reales wasn't the mint equivalent of being made to peel potatoes...
Your piece happens to be on a very nice level planchet, allowing a large amount of detail to make it on the coin (no big "flat spots", or areas on the planchet that were never imprinted). In addition, what made it onto the coin is mainly the upper portion on the design... so your piece caught most of the Philip V "PvS" monogram, a bold mintmark (though it missed the assayer mark, which would be "L", just beneath that), and much of the crown. The best part is that it also caught a perfectly clear "03" of a 1703 date.
Hold off on cleaning with anything besides water and a toothpick... could probably use some educated improvement, but it's a nice little piece as is, so don't ruin it.