If you add the groove depth to the .445 bore diameter, you get a groove diameter of .465".
Way too big for good results with .458 bulllets even if the rifling twist stabilized the bullet.
1 in 56" is for round balls and maybe some hollow base Minié bullets.
If a Minié bullet has a deep enough hollow base, it will actually be stable if shot from a smoothbore. Air rifle pellets are a good example of such bullets. If you have a BB gun, try loading some .177 pellets from the muzzle and shooting them, they always hit head first because of their forward center of mass.