To sort of expand upon what I've stated: The English practice in those days was to use the basic case designation first, followed by the modified neck size, then add modifying nomenclature. The cartridge to which I refer was the ".577/450 Revolver." And, as I stated. bullet diameter was around .600", making it probably the largest in bullet diameter.
The English were prpoponents of large diameter, heavy bullets, moving at low velocities as a measure of stopping power. Results of this thinking were the .476 Eley and the .455 Webley revolver cartridges, and the .505 Gibbs, .577 Nitro Express, and .600 Nitro Express hunting cartridges. At the time when the Sun never set on the British Empire, British sportsmen were hunting lions and tigers and bears, in the most gentlemanly way. Large caliber handguns, as has been noted, the Howdah pistol, were a back-up should an irate tiger decide to cohabit your space on an elephant's back.
And, on the same subject, in the late 1800's, Winchester necked down their brass 10ga. shotgun shell to accept a .75 caliber bullet. I forget the complete nomenclature, such as .75-120-650, or something like that. The gun was the Model 1887 lever action shotgun. Not too practical, just a "show it can be done" type of thing.