"I think you could make the case that the .44 special is THE seminal S&W round; without it the company might well have folded in the 19th century"
Except for the inconvenient fact that the .44 Special wasn't introduced until 1907...
And, to the best of my knowledge, it was only chambered in Smith swing-cylinder revolvers, not in any of the breaktops.
Also, I think it's pretty hard to say that the .44 Special is a seminal round for Smith & Wesson. It was never really that popular, whereas shooters positively leapt on the .38 Special and, especially, the .357 Magnum,rounds.
No way would Smith have folded in the 19th century without the Russian military contracts.
Two words -- pocket revolvers.
S&W's small guns, like the rimfire No. 1, 1 1/2, and 2, put the company on solid financial footing by 1873. The later centerfires, especially the New Century hammerless guns, made it an absolute powerhouse.
The rounds that S&W introduced for those guns, the .32 S&W and the .38 S&W, were so popular that they swamped Colt's similar offerings to the point that Colt, to keep something resembling parity in the small gun market, was finally forced to start chambering its revolvers for the Smith & Wesson rounds -- quite a bitter pill in those days.
The large, break-top No. 3 revolvers, on which the Russians and later Schofields were based, were certainly popular in their day, but nothing like the Colt Peacemaker. Because its production capacity was stretched close to the limit providing guns to the Russians in the early to mid 1870s, S&W had to largely surrender the large-frame civilian market to Colt, Merwin & Hulbert, and a few others, and by the time that they could get into the mix in a substantial way, Colt was ruling the roost and S&W had to try to play catch-up for many years.
S&W probably could have done a lot better in the large handgun market had they only chambered the No. 3s for .45 Colt, and earlier for the .44-40 and .38-40 Winchester rounds. But, that would have meant taking the bitter pill that Colt was forced to swallow.
Smith's .44 S&W American and .44 Russian rounds were quite popular, and the .45 S&W (the Schofield round) also met with quite a bit of use in the old west, but they never approached the popularity of the .45 Long Colt or the .44-40.
When the military dumped the S&W No. 3 Schofields, many were picked up by Wells Fargo and used by the freight police, while others were sold through several large hardware outlets across the country.