Here is the chamber cast I made this morning of the Springer rifle
Here are the dimensions:
Overall case length 56mm the end of the case isnt clear but we used the black dot as the likely length.
Rim of case to start of rifling 63mm
Rim diameter 14mm
case diameter at breech 11.5mm
case mouth diameter 10.25mm
bore lands 10mm
bore grooves 9.75mm
This is a round with a slight taper from the breech to mouth end and no neck like the Springer 11.75x52R round.
I've tried to be as accurate as possible here but there may be slight variances in these measurments.
BTW: The gunsmiths stated and I agree that the rifling is of the gain twist variety.