This Springfield Armory manufactured fifth or sixth variation breech block with the low arch is stamped "U.S. / Model / 1873" and is for the model 1873 trapdoor rifle and carbine. This breech block is in very good condition exhibiting a grayish brown patina withscattered specks of older rust and/or pin prick pitting and possibly faint traces of mellowed original case colors in protected areas.  (file photo)

Note: Trapdoor rifles and carbines manufactured between December of 1878 through December 1886 and having serial numbers between circa 99,500 through circa 360,000 would have been manufactured with the fifth or sixth variation breech block.