If you are gonna go brass go lots of brass, the whole neighborhood:
Is the 1866 Yellow Boy a .44-40?
The Yellow Boy was an updated Henry.
The original Model 1866, manufactured from 1966 to 1873 was only chambered for the .44 Henry Rim Fire, as was the Henry, BTW.
Any other chambering is a modern reproduction.
The 1866 model went out of production in 1873, being replaced by the famous Wincheser '73, originally only chambered for the .44-40 (AKA: ".44 Winchester") center fire cartridge. Both the Winchester '73 and .44-40 were introduced in December, 1873. (Winchester records say there was a sufficient warehouse supply of both to market them.)
The .44-40 has been in continous production since. It was converted to a smokeless cartridge in the 1890's
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The .44-40 Winchester is the
second oldest US cartridge in continous production since it was introduced.
The venerable .45-70 "Government" was introduced in May,1873, so is just 7 months older. It was also converted to smokeless in the 1890's, though at reduced pressure than the black powder load, so it would be safe to use in the original Trapdoor Springfields still in use by civilians.
Both remained in production during WW1 and WW2. A lot of cartridges production was halted during WW2 were never put back into production.
The .45-70 even remained in production the 70 to 75 years no new rifles aside from a hand full of individual custom rifles were made in .47-70.
There were a LOT of 1873 Springfield Trap Doors, Remington Rolling Blocks, and Sharps rifles still in use for hunting and "1,000 yard" (it was actually 1,010 yards) shooting matches, during the time no new rifles were made for it until 1974/1975 when Marlin re-introduced their model 1895 for the upcoming Bicentennial.
. I had to go check these out over at CK because you posted this 
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