I don't know how much this reply will help you, but here goes anyway.
I have on order currently a barrel to finish at 31" swamped octagonal measuring breech at 1 1/8", muzzle dia across the flats of 15/16". the bore is .6750, twist is 1 in 95". This will be stocked as an English Gentlemen's rifle and be a flint ignition rifle made to shoot 16 bore round ball.
There are Purdy rifles that are still around that are in 12, 10, 8 and 4 bore. These were the cutting edge DG rifles of there time period.
When I started on this project I found people with original guns and got their input. So yes, I've heard of them.
I hope that helps to answer your question.