My understanding of the reason why patched round balls typically do not shoot well out of fast-twist modern barrels is that the faster twist of the rifling will essentially shred the patch. Judging from the patches I recovered after attempting this, it makes some sense.

People have had luck getting round balls to shoot out of fast twist barrels, myself included. But typically it requires reducing the powder charge below what you would want to shoot a deer with. One of my fast-twist caplocks shot round balls well as long as I only used about 50gr of powder.

But each gun is different. All you can do is try. Otherwise you could go to a conical and still avoid sabots if you want.