This is not correct the 50-140 Sharps did indeed exist it was introduced as special order cartridge for Sharps-Borchardt Model 1878, circa 1880 at the very tail end of buffalo hide hunting. Winchester loaded this cartridge as well but they called it the 50-140 Winchester Express and was loaded in the Winchester Hi Wall rifle. Both the Sharps and the Winchester cartridges where loaded with a 475 grain paper patched bullet (PPB) at advertised velocity of 1580 FPS, with 2530 FP, or it could be had with a 700 grain PPB 1355 FPS, and 2850 FP. Because it arrived at the end of the viable Buffalo hunting years very few rifles where built in the cartridge, there simply was no longer a need for a cartridge with such power.Just as a technical correction, there never was a 50-140 Sharps. In fact, it's doubtful if any 19th century rifle manufacturer ever offered this chambering.
fo those shooters who are interested in authenticity, the 50-90 would be a better choice.