There are a few inconsistencies in Forsyth's book as pertaining to ballistics as we know them today.

I assume that if there is indeed a difference in recoil between a rifled 14 bore or identical build to a smooth 14 bore, both with identical patching and ball weight, it would most likely be unnoticeable to the shooter.

Another "Book" claim re: velocities:

We have tested the claims of higher velocity with a smooth bore with a given charge against a rifle of the same size, with the same length of barrel and charge. The results were within normal shot to shot variation.