Found my micrometer and ran a ball through the barrel of my .31. It may vary by manufacturer, but my Uberti has a .31 bore with shallow rifling--.01 or so. The .321 ball gives good accuracy for me in this gun.
The Dixie Catalog (the paper one) says the Uberti 1849 Pocket Revolver has a .310 bore and 7 grooves .332 diameter (grooves are .011 deep).
It has a 1:48 twist.
The Uberti 1848 Baby Dragoon has the same bore dimensions.
The cylinders chambers should be .319 if the catalog is correct.