I do not have one of these double barreled 12 bore or 8 bore guns - but - I would still call an 80" twist in 12 bore, to be a round ball twist.

There are guys here with cape rifles and rifled doubles in 12 bore made for slugs that must know their twist rates.

I know for a fact, that back in the 1850/60's many English makers even thought that 36" in a 12 or 13 bores, was a round ball twist. Of course, we know today, that is ridiculous. Seems in 10 to 20 years the makers became more enlightened, and started making slower twists for round ball guns. Forsyth was a prime instumentalist if this 'move' along with the few makers he'd been able to 'get through to' wo actually slowed down their twists as early as 1850. Most did not.

I'd love to have a modern ML gun for round ball at 80" twist in 12 bore - a double would be even better.

My own 14 bore Ml rifle routinely makes 1" to 1 1/2" groups of 5 at 100 meters and recently a 1 1/4" group X 3 1/2" at 200 seated rest shooting for 6 shots. Granted, it's a .69 single shot, but that's with round balls, a 66" twist and 6 drams of powder. The loads show that the twist is connnected to the accuracy. I have a hard time thinking of an 80" twist as being for a slug. 30" to 60" yes - short conical, minie type (poor for hunting).

BTW - those rifling photo's are wonderful. A reloader's dream come true.