With regards to the ammunition used by the British for their Colt's Revolver, I have the bullet written as being 84 gauge, which I think is the equivelant of .357 inch. Can anyone confirm that 84 guage is .357" please?, it's an area that I don't know much about. Thanks in advance, Adrian.

The only contemporary table I have to hand is in Hans Busk's "The Rifle" (published 1859). This stops at 64 gauge which is equal to .421 dia of bore.
 
David

Cartridge collectors often find "90 Bore" labels and "carrying 90 balls" in references for the navy caliber on the west side of the pond.  I believe that the numbers are more nominal than technically accurate.
It becomes even fuzzier when measurements are taken from surviving specimens, as oxides and waxes change things irregularly.
Acceptable tolerance for lead balls has always been rather generous on the + side.
Cheers,
Ross