Springfield Trapdoor mod. 1865 to 1870 lockplate is the same as the one
used for the 1860 muskets except for the notch for the tumbpiece.
The mod.1873 to 1888 had new lockplates designed for the 45-70. The lockplates are marked with the spread
Eagle and, the full word Springfield (and the date 1873 on early mod.1873
rifles and carabines).
There have been some
lockplates that have shown up with an 1883 date on them, however these
were second quality lockplates that were sold off by the armoury and
were later stamped by a "surplus dealer"and used to make
trapdoors out of parts.