You have a nice 1787 Miller 48-g.5 Rarity 5 (I will check my latest catalogs, it might be lower nowadays) but regardless a nice Conn copper. I am not 100% sure of the Obverse side attribution, but it does seem to match the Miller 48 Obverse more than the other possibility when you have a g.5 reverse, which would be a slightly rarer variety match of a Miller 24-g.5. But from what details I see I am going with the M.48-g.5.
The details on the Obvese side that would help confirm are still coated over with crud,the area where the last C is in CONNEC and the area right after RI in AUCTORI.