[JustinL]

Are these calibers actually the same thing? If not, are they still interchangeable?

[Oro]

I believe the Eley rounds have a slightly longer case. As to diameter, pressure, etc. you are ok, but I think it will be a function of which case it is bored for. If Eley, then either work. What are you actually trying to do and in what gun?

[JustinL]

I am curious b/c I've seen ww1 era webleys chambered for .455 webley and Colt New Service revolvers of the same vintage chambered for .455 eley.

[rcmodel]

It's a long & confusing road!

.476 Eley = British caliber used from 1881 to 1891 in the Enfield revolver.

.455 Revolver MkI = Shortened case. Black-powder load first used in the Webley in 1892.

.455 Revolver MkII = Improved Cordite round adopted in 1897.

This went on through the MkIII, MkIIIV, MkV & MkVI in British service.

.455 Colt = Colt's name for the .455 MkI/MkII, etc.

.455 S&W = S&W's name for the .455 MkI/MkII, etc.

All four rounds can be used interchangeably in Enfield & Webley revolvers.
However the .476 Eley may not chamber in later Colt & S&W revolvers chambered for the .455 Webley because they had tighter chambers then the British guns.

rc