Dugaboy, a side by side combination gun with a rifled and a smooth barrel is a Buechsflinte when it have the rifled barrel on the rigth side. This is most times of german/austrian origin, also belgium. Husqvarna in sweden makes it also regulary in 9,3x57R360 (360BPE 2,25"), 12,7x44R sweden and also for a rare group of cartridges you have a hard time to find any info's about, but more later.
Americans call all combinations guns with a riflled and smooth barrel "cape gun" because they dont know it better. I am do this also because you dont have to explain any times what for fine differents are.
Let me tell you: most of this guns are in fact no cape guns, this is a british term to describe a combination gun with the rifled barrel on the left side and the smooth on the rigth. You understand what I mean, we on the continent drive with the car on the rigth side, the british do it on the left. Dont know realy why but the british when thinking technical problems turn all things on the other side then we do.
I believe only cheaper cape guns are made in belgium for export to britain or the colonies but on the continent it was allways a Buechsflinte. I dont think that many cape guns was used on the british islands, the most go to the cape as farmer guns, not to forget the paradox gun was a strong rival for such a combination gun.
We have here the privileg to use the metric system and also understand imperial measurments

Shotgun cartridges have the gauge number and the shell lengt in mm: 12/76 = 3 " shell
16/70 = 2 3/4 "
20/65 = 2 1/2"

I wonder that you dont know this in the states, Winchester ammo boxes here have allways booth measurment printed.

A rare class of cartridges are the in old german ammo catalog's so called Lancester Bullet Cartridges, lancester was a synonym for center fire shotgun cartridges. Same bullets and lefaucheux cases are use for pinfiire guns, tinker here have a double rifle for such a cartridge. You find 33, 40 and 50mm long cases but 40mm was the rule. Its not a paradox, much older, and allways for full rifled barrels. The bullet is the Cats head bullet, you find it in the rws bullet catalog for brass and paper caseswith different diameter but the stop ring is the same. notice: see never 40mm paper shells, only the rws brass, thing anyone like to have paper make it with a knife from 65mm long shells.
I think that this are the oldest breechloading hunting cartridges on the continent, maybe also in britain, its the first generation before the 45/11mm comes around 1870.
Where and when do it starts? maybe in france around 1855 with lefaucheux guns and than quickly adapted for the center fire shotgun cartridge.
Have a book: Adolf Zimmer "die Jagdfeuergewehre"( the hunting guns) from 1877 and he only knows this kind of hunting cartridges for rifles than.
I have neve seen a loaded cartridge in a ammo catalog, only brass and bullet so we have to see here the missing link from muzzle loaders to breech loader with ammo out of the box. its was only a handloading story.

the husqvarna 17A was made in 20/65 - 28/40 LK ( LK means Lancaster Kugel =bullet in old german ammo catalogs)

20/65 - 24/40

16/65 - 20/40

with my gun ,rifled and smooth barrel have the same dia. on the muzzel, unusual for a cape gun

I am very in doubt about your Hafner in 58 Berdan, this cartridge is very similar to the 24/40LK and when the gun wasnt made for export into the USA it is indeed. I dont know them all, of course but there was never a german gun for 58 berdan. Give the measurments of a chamber cast and slug the barrel.
Magtech brass works very well in such guns but they are blackpowder only. I cut the magtech brass on the lathe and aneal it, have a homemade resizing die because the chamber is a little bit tappered.
100 grains ffg behind a 480 grain Minie bullein the little 28/40, load with a 577 snider NDFS die. A 585 Lee Minie mould was at home when I got the gun, made a hammer slug die because barrel shows .600 dia.
I thing the magtech brass stand the blackpowder pressure very well, havnt a splitted case till now and its not realy nessesary the resize after such a powerful load.

hope to give you some news about this, needed years to find informations

sincerely yours

Husqvarna, i visited a hunting guns collector in june, he had have Husqvarna whaling gun. have you ever seen this, very strong 12 ga smooth barrel bolt action with fore and rear sigth shoting the harpoon with blank.
I believe it was made only for small whale and seals in norway, knowing the old greener whaling gun and the Foyn canon.