Howdy
Did you consider slugging the barrel so you can find out for yourself? It is really very easy to slug a barrel. If you want instructions, just holler.
Not to be too much of a school marm, but the correct term is rifling groove diameter. Bore diameter is the diameter of the lands of the rifling, in other words, the diameter the hole was drilled, or 'bored'. After the bore is drilled, the rifling is cut a bit deeper.
Uberti has been using .429 diameter barrels for all their 44-40 guns for a number of years now, however I have a Winchester Model 1873 replica made by them back in the 1980s that slugs out to .427. Can't tell you about Pietta, but I know how to slug a barrel.
I have always used a plain jane set of RCBS dies to load 44-40, never bothered with the fancy 'Cowboy Dies' with their silly brass locking rings. The standard die set is set up for .427 diameter barrels. When using larger bullets for .429 barrels, sometimes there is too much friction as the bullet is seated. This can cause the brass to buckle down below the bullet. So sometimes the expander plug from a 44 Special/44 Mag die set will help expand the neck slightly more to reduce friction.
You may or may not want to invest in the Lee Factory Crimp Die to go along with your die set to help with crimping. It is perfectly possible to crimp with the standard seating/crimp die, however you have to be very particular to get the dies set just right. 44-40 is not as forgiving as some other calibers.
Regarding bullet diameter, I have five 44-40 rifles Some are antiques, some are not. They all have either .427 or .429 barrels. So I comprimised on .428 bullets for all my 44-40 rifles some time ago. I have two old 44-40 revolvers, a Colt New Service and a Merwin Hulbert, but unfortunately they have five groove rifling, so it is difficult to get an accurate measurement when slugging the barrels. They do just fine with my .428 bullets.
Holler if you want to know my other trick for preventing brass from bulging under the bullet.