The original Webley MKI Service Revolver --although a .455--was initially called a ".442" as this was the bore diameter, not the groove diameter
. Eventually it became the .455 Webley and served the Brits in a long series of homely--though highly efficient--sixguns.
According to one source, the groove diameter
of Winchester and Marlin rifle barrels is 0.427 inch, whereas Remington rifles have 0.425-inch groove diameters
Any barrel's groove diameter
that measures from .3080 to .3095 inch is acceptable.
Following this deep drilling and reaming, the rifling grooves will be formed, resulting in the groove diameter
essentially the same diameter as the bullet.
Grooves are deemed to be oversize when the groove diameter
exceeds the nominal rope diameter by more than 15% in steel or 20% in polyurethane liners.
I was under the impression that the barrel groove diameter
for these revolvers was right at .360".
I size conical bullets to the groove diameter
and spherical balls .
For this reason, the initial intension of wear evaluation by measuring the groove diameter
was changed to gravimetric evaluation.
You can fret about whether that actually means bore (land) or groove diameter
; conventionally it is bore.
The diameter measured to the outside of the blade determines the limit for the smallest possible diameter which can be machined, and the diameter measured to the inside of the blade determines the limit for the largest possible groove diameter
Chris Scherf, GW's tooling engineer for the project, explained that the part design specification required the outside diameter and O-ring groove diameter
to be within 0.001 inch, and the parting line mismatch had to be held to the same specification.