The Trapdoor Breechblock system
On top of the breech are the marking "US rifle 1973" either with or without an eagle's head and crossed arrows. Only early mod1873's had the eagle head and crossed arrows these markings lasted for about 1 to 2 years, then the breechblocks just had model 1873 stamped on it. On the later mod1884's is the date 1884 seen.
The early high arched breech block with eagles head and crossed arrows is only correct on the early mod.1873 and the lockplate on the rifle or carabine should have an 1873 stamped under the word Sprinfield. These breechblocks did not have color case hardening. They were case hardened but solid black in color.
The
serialnumber is on top of the reciever. The notch for the
thumbpiece is clearly seen on this photo. There is also
an good example of color case hardening on the
breechblock.