Quigley is shooting a Model 1874 Sharps chambered in .45-2 7/8". Here is mine (from C. Sharps Arms of Big Timber, Montana), chambered in .45-2.6":
At the dawn of metallic cartridges, they were often designated by caliber and case length, as I did above. Lots of folks today use the caliber and powder capacity, i.e. ".45-70" (actually .45-2.1"), ".45-90" (.45-2.4"), ".45-100" (.45-2.6"), and ".45-110" (.45-2 7/8"). (The .32, .38, .40, .44, and .50 calibers had similarly varying case lengths and capacities, but I'll stick to the .45's to try to explain this). The problem was, for example, the .45-2.4" and .45-2.6" cases, as loaded by Sharps, both often used 100 grains of powder. The ".45-70" was often loaded with 50 or 60 grains of powder, and so on. It turned out to be better to list case length, so customers would know what ammo would chamber. The box would also list the charge in grains, as well as bullet weight in grains.
All Sharps ammo (and Remington rifle ammo) for the big single shots was originally loaded with paper patched bullets. It was really more of a paper jacket, the predecessor of the copper or cupro-nickel jacket. Government ammo for the Springfield was unique in that it used grease groove bullets from the get-go.