Most commercially mass produced muzzleloading guns today have button rifled barrels. There's nothing wrong with them, other than the rifleing is rarely over eight thousandths. This is primarily where the swabbing after every shot came from. Several of the old timers at Friendship back in the day, cut, and recut, their barrels to the shallow side on their target rifles, and said they sealed up better, and were more consistent.
The softer the wrought iron, the better the old match shooters liked it. They swore it never shot slick, and freshened out easier, and so smooth it didn't require a lot of break in shooting. The old match shooters would have run from these diamond hard barrels like their hair was on fire.
Hungry Horse