I have this 1908 O Barber quarter and it weighs 5.84g. I know they are supposed to weigh 6.25g. is this from wear? That is a difference of 0.41g. That is an awful lot of weight to cut considering it still shows some pretty good detail. Yes, its definitely circulated!
The supposed to's and should haves...there are 1) tolerances 2) manufacturing differences, including the alloy, stock plate thickness variants among others 3) then slight wear. Any circulated coin will be different, above/below, you name it and in what combination. I don't get my knickers in a knot unless there is a 1g difference, then you may have "something", error or fake?
Try dealing with the ancients(lotta wear/corrosion) and actual counterfeit detection, there's where you see disparities among weights/materials!