You are correct about the1873 date.
The .44-40 was also adapted to handguns, where its rimmed design made it ideal for use in revolvers. It became one of the most popular cartridges for the famous 1873 Colt Single Action Army revolver, along with the classic .45 (Long) Colt cartridge, also introduced in 1873.
And I think the .44 WCF (.44-40) wasn't chambered in Colt revolvers until 1878.
It wasn't common back then for any manufacturer to chamber their firearms for somebody else's cartridge. Not sure, but Colt may have been the first to do that, with the three Winchester rifle cartridges (.44 WCF, .38 WCF, .32-20).
This wasn't all that long after "cartridges" as we know them today had come into existence, anyway, and lots of this was "developmental" (build it while you fly it).
-Chris
