Except... the button in the photo does not have an RMDC (Raised-Mark-in-a-Depressed-Channel) backmark. It has a depressed-letters mark. Also, the button's "Scovill M'fg. Co. / Waterbury." (note the period after Watrebury) backmark without any encircling rings or encircling dots (etc) means it is from 1870-to-1890. Info-source: the book "American Military Button Makers and Dealers; Their Backmarks & Dates" by William F. McGuinn and Bruce S. Bazelon.