One thing to keep in mind is that the original Trapdoor Springfied rifles and carbines were sighted for something like (can't locate the exact figures right now) 324 yds and 228 yds respectively with the original sights (M1873R and M1873C and M1879R and M1879C). The trajectories of the .45-70-405 cartridge and the .45-55-405 round were such that the arms shot 15-18" high at 100yds depending on what loading was fired in which arm, with the lowest sight settings. What complicates things, especially on the original carbines is that some of the company commanders requested and were issued rifle ammunition with possibly a change of the rear sights to the rifle sights. M1873 carbines especially are often found with the rifle sights. Some (most) collectors tend to retrofit any carbines that have the "R" rear sight with the "correct" "C" sight. This may be okay, but it is altering history for that arm. Whether putting a rifle rear sight on a carbine that was shot with rifle ammo would have compensated for the different trajectories of the two rounds or not, I couldn't say. The original sights were installed at the arsenal with slotless screws. When you find rifle sights on the carbines you will find the screws have slots in the heads. In most instances, M1873 carbines (s/n below 50,000) found with rifle rear sights will also have had their thin wrist, short comb stocks replaced with the thick-wrist, long comb M1877 stocks. If they have the earlier stocks, the chances are they left Army control with a deserter and probably have carbine sights. Those that stayed under Army control most likely received the field or arsenal modifications. I have no idea what the modern repros have for sights, even if they look like the originals.