The .577 Snider round is a 480 grain bullet ahead of 70 grains BP with 2 inch/ 1 78" case, although Hoyem lists a 1.65" case with the same 70 grain load

All the British Ordnance (military issue)rounds were coiled brass, as was the .577/450

The only .577 alternative for handguns was the .577 revolver round, much shorter and less powerful

Note: the 4 barrelled Lancaster pistol was not offered in .577 IIRC, but the 2 barrelled O/U was in .577 revolver

These Double barrelled hammer pistols are the most interesting IMHO so if you like one go for it!

TH