Jack,
Those two measurements, 0,405 and 0,454, are for nominal 40 caliber and nominal 45, NOT bore and groove.
Why would they make a rifle chambered for 45-60 and 45-75 Winchester and then have the barrel dimensioned for 45 Colt? Am I missing something?
Mike Venturino gives 0,457-0,459 for cast bullets to be loaded in 45-60 and 45-75. Furthermore, he states "every .45 caliber Model 1876 whose bore I have personally slugged has measured .457 inch."
Mike gives 0,406 for the 1876 he tested in 40-60, so, maybe the 0,405 number given on the German site is actual groove-to-groove diameter.
Lars