A 71/84 should normally have a bore diameter of about .446" Maybe a little larger depending on wear and tear as well as the quality of the tools used to make it 140 years ago. A Model 71 generally has a bore diameter of .451" In general, I would think the commercial ammo should be sized for the .446" diameter, as 71/84s seem to be more common than 71s.
That CIL ammo should be smokeless, at least the ammo my great uncle had was. The CIL brass is not the best for reloading. It has a balloon head and the brass tends to split. If you plan on shooting it, I suggest you source some Bertram brass. It is expensive, but has solid head construction. I bough mine at Rusty Wood's Trading in BC and had it shipped to me. Loaded with black powder, I didn't need toresize it before loading again. I'm not sure how many firings I will get away with before resizing. Availibility of .446" bullets is better than .451"