Spudnutt wrote:
> The initials read WKC.
The photo shows the letters are WSK, not WKC. WSK presumably represent W. Stoke Kirk, an arms-dealer company in Philadelphia from 1874-to-1976. After its founding in 1874, the W.Stokes Kirk company purchased enormous quantities of civil war suplus armaments and equipment at US Government auctions, and then re-sold the stuff to foreign governmment armies and the American public.
Your eagle breastplate is not missing its filler-metal, it is an "unfinished" one. W. Stokes Kirk purchased vast numbers of leftover "unfinished" insignia (missing the attachment-hooks, etc) from the US Government's wartime stockpile. Apparently you've got one of the W.Stokes Kirk company's leftovers. Unfortunately, there's no way to know whether your breastplate-front was manufactured during the civil war or not, because W. Stokes Kirk also purchased the original manufacturing stamping-dies for US buckles and breastplates -- and used those dies to make copies in the 1870s-1890s for civil war veterans organizations.