That's the third Colonial copper that we pulled from this site--the other two were the 1787 CT Halfpenny and a KG III that is also toasted unfortunately. I went back yesterday and unearthed another two large flat Tombac buttons (for a total of three so far) and an interesting "What Is It" with two loops and a hook that kind of looks in the shape of a trilobite--it's quite light, but has a lot of detail.
I hope you can get an ID on this odd copper Grant. Seems like the 22mm dimension is the original radius of the coin.