I'd assume the lack of good documentation is because muzzle loaders simply aren't firearms in most American states. Can be bought through the mail with no background check, so theres no great need to be overly formal with the gun description. Its not something our American cousins would have to be concerned about whether its in theory a .44 or .45.
Mr Rollo - I think you'll find that it is the general attitude of our US cousins to blame for the lack of correct use, rather than the lack of instructions.
Litiginous USA is a by-word for the way that the ysue at the drop of a hat if there is anything that they can possible sue for, and certainly NO firearm could be sold in the USA without a comprehensive set of instruction on how to use it correctly. In fact, my Redhawk instructions even include a firm admonition NOT to climb trees with the revolver cocked.
As one famous American once said, 'when all else fails, read the instructions'.
Logically then, if we are unable to define calibre, there is little point in discussing say whether a gun is .44 or .45 as there is no means of validating the assumption.
Ruger Old Army 44, Rossi Puma 357, Armi Sport Le Page, Parker Hale Musketoon, Pedersoli Mortimer, Lee Enfield No 4, Weihrauch HW95K & HW90, Original Mod 5, Diana Mod 5, Webley Senior, Webley Falcon & Jaguar, Daisy, Baikal S/B, Arquebus.
For our purposes in the UK in relation to certification, the calibre is whatever the maker stamps on it......