This 1866 model was the 1st Uberti that I acquired, 15 rounds in the tube and one chambered!
When they 1st came out with this model it only came in the original caliber.... 44/40
Original caliber of the Henry and the improved Model 66/1866 was .44 Henry Rimfire.
.44-40 came out in November or December, 1873, a few months after the .47-70. (best I've been able to narrow down the .45-70 for Civilian sale/use is sometime between March and May, 1873.)
Both the .44-40 and .45-70 are the longest continuously produced center-fire handgun and rifle cartridges respectively.
Neither have been dropped from production since they were introduced.
.45-70 cartridges were made even during the 60-70 year period when the only new rifles for it were custom rifles, which includes the WW1 and WW2 years, when hundreds of cartridges were dropped from production during each war. (Most, if not all of which, are still not made.)
The first Winchester chambered at the factory for .44-40 was the model 73/1873, that first shipped from the warehouse in late December, 1873/Early January, 1874. That's the earliest I've found that Winchester had "warehouse stock" of the model 73.
Post 1873/1874 manufactur Model 66/1866 Winchester were available in .44-40 and the original .44 Rimfire.
The Henry was dropped from production in 1866. None of the original Henry's were made in .44-40. Only the modern reproductions.
(So if anyone tries to sell you an "original" 1860's Henry rifle that's chambered for .44-40, it's a modern reproduction. You can "take that to the bank" and save a few bucks.)