I've been meaning to post this for you with some extra things to look for. Here is one fake for comparing and one genuine breastplate from the battle of Franklin. I found it myself next to a horseshoe while digging for a conduit install.
1) the size of a fake will usually be smaller than the real one. It's important to check the reference books too like O'Donnell's military belt plate book for average sizes in millimeters. Don't take it as the only answer though, if the the book says 55mm and yours is 54mm, that alone does not discredit it."Burnside" plates are smaller with a different design but once you determine a maker die style like Pittman or smith or Boyd&Sons it'll help.
2)weight and lead fill. Fakes usually have way too much lead and it balloons over the edge. Real ones usually should be filled flat or slightly concave, loop distances are not identical but do have a certain distinct shape. The fake one here has loops that are way too long and it's overfilled. The loops usually grey or become rusty and the fill starts to flake on some from PH levels in the soil and passage of time for the real dug ones.
The loops on yours look a little too thin and the fill looks fresh but those are some more tips. You'll see all that stuff I mentioned in the pictures and I even laid them on top of each other to show the size difference in the second picture. There's other things about the rim but I can't really explain them without holding them. I hope this helps you out.
View attachment 455905
View attachment 455906
View attachment 455907
View attachment 455908
View attachment 455909
View attachment 455910
View attachment 455911