The bore of my 1881 is .458” so the grooves must be something like .466” or so.
I haven’t got very good accuracy with my rifle yet primarily, I think, because my bullets have been undersized for this bore.
Now, however, I can swage bullets of any weight that patch right up to .458” so with a little work I am sure it will shoot great.
My other 450No.2 Musket chambered rifles have tighter bores so shoot .458” bullets just fine with smokeless but use a .450” paper patched bullet when using black. They both shoot quite good with either black or smokeless.

You will probably find that your chamber doesn’t have much of a lead into the rifling from the case mouth with the rifling running right up to the case mouth. With a chamber like this, bore sized bullets are about as big as you can chamber so they often don’t lend themselves to using smokeless very well.