that my friend is a union "Williams" type "cleaner bullet" the base "scraped" the barrel clean --one was issued in each 10 round packet of bullets -- the old guns used black powder and after several shots the fouling would clog up the barrel make pushing down the bullet next to impossible --so troops were told to use a cleaner bullet every so many rounds to keep their barrel clean --because the base made it a bit hard to ram home some troops "discarded" their cleaner bullets * however by the looks of it yours was a "fired" round.