Could be a .44XL they were tapered. I can’t find any dimensions for it though, maybe somebody else has some. That would make Bavarian doubtful though, it was more or less a US calibre. So US or maybe Belgian. You never can tell though, some Bavarian gunmaker could have cloned the calibre.
I have found some now. Dimensions are not great for a match. The rim space on the chamber is bigger but that could be easily explained away as a comfort fit, the base is good but the mouth of the chamber is a bit small. The critical dimension now is length.
Often with these old guns the chambers were loose so plenty of latitude has to be given when assessing them. could your neck dimension actually be bore size, ie no seperate cone just a straight taper running all the way down to bore? That would be expedient from a practical point of view. Bore should be .425" but a tighter bore is not inconceivable. They did need to break up the wooden shot cup before it exited the barrel. Presume the dimensions came from a sulphur cast so how good are they?.