This Springfield Armory manufactured fourth 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 brownish gray patina with scattered 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 March of 1878 through December of 1878 and having serial numbers between circa 81,000 - 87,000 through 99,500 would have been manufactured with the fourth variation breech block.

Note: U.S. Springfield Armory model 1873 trapdoor firearms with the following serial numbers have been observed with this part: 89587