Donnelly's 2nd Edition (p. 157) indicates that the .256 Gibbs Magnum shoots a .264 bullet, but states the Nonte gives the bullet diameter as .266. It seems strange that a cartridge that shoots a .264 or .266 bullet would have .256 as part of the name.
Does anyone own or shoot this cartridge? If so, what is the real bullet diameter that it shoots?
Regards,
HockeyPuck

.256 is probably the land diameter rather than the bore diameter. .266 minus .256 = .010, or .005 rifling groove depth. Lots of different ways to describe the same thing in the gun world.