I'm planning a .461 Gibbs No. 2 build on a Martini action and cannot seem to nail down bore and groove diameters of original rifles. I have heard specs ranging from .452 up to .470. The Imperial War Museum gives .448 as the diameter of a bullet in a .461 No. 2 cartridge in its collections, but my guess is this is the naked lead bullet that was paper patched up to a larger diameter.
Does anyone have reliable information on groove and land diameters, and possibly rate of twist?
Many thanks.