All I can go by is what I've owned, or had a chance to look at. That said, I'd have to say that most, but not all, 18th and early 19th century rifles had swamped barrels. The swamp varies with maker and time period, and overall probably wasn't as pronounced as the barrels made today. I think the earlier ones had more swamp than the later ones.
As example, a 52 cal J Dickert signed barrel I have has a breech of about .980" the waist is .878" and the muzzle is .950". This doesn't seem that much different than a modern barrel.
Once you get to about 1830/40 or so, swamped barrels seem to have disappeared for the most part.
As usual, just my opinion,
John