I dug this today at a home site that dates back to at least the early 1900s, possibly late 1800s. It's obviously military and I think it is a lapel pin. I guess it could be WWII, WWI or even Spanish-American War. One inch diameter.
Confirmation: Dating Metallic Insignia: Collar Disks
...and for anybody who doesn't already know, the crossed rifles mean it is the 114th US Infantry regiment.