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 mixture of applied hot immersion blue finish with a brown patina and having a few specks of older rust and/or pin prick pitting.  (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.

Note: U.S. Springfield Armory trapdoor rifles with the following serial numbers have been observed with this part: 130964