(Pic found on the 'net.)
Another well known muzzleloading smoothbore was the French Fusil de Chasse. I have one in 20 gauge from Middlesex Village Trading Company.
(Pic borrowed from MVTC.)
Being smoothbores, they can shoot birdshot, buckshot, or a single ball, making them useful for any game from birds and squirrels on up to moose. They also saw a lot of use as fighting weapons. The modern equivalent would be a single shot shotgun like my old H&R 20 gauge.
When the muzzleloading single barrel shotguns were state of the art, most were produced in smaller gauges -- 24 to 20 gauge. They were cheaper to load, requiring less powder and shot, important when you are weeks or months away from resupply.
Most of the currently produced muzzleloading shotguns are 12 gauge doubles, and most of the single barrels are flintlocks. Pedersoli lists a percussion version of their Mortimer 12 gauge shotgun.
One percussion single barrel smoothbore that was imported for awhile but is no longer was the Euroarms of America "Magnum Cape Gun." Normally, a cape gun is a double with one rifled and one smoothbore barrel, but I guess EOA thought the name sounds cool. The gun was made by Investarms* and is still listed on their website as the "Gallyon," but doesn't appear to be imported into the US at present.
One of the Magnum Cape Guns has been on my want list for awhile and I found one in excellent shape yesterday at Dixon's for a reasonable price, so it came home with me.
It's a 12 gauge percussion smoothbore shotgun with a cylinder bore, i.e., no choke. The bore appears to be chrome lined, which will help cleanup. The barrel is fitted with a hooked patent breech, so if you remove the ramrod, drive out the barrel wedge, and put the hammer on half cock, you can lift it out of the stock. You can then dunk the breech end in a bucket of water and using a wet patch, pump water through the bore to clean it.
The Magnum Cape Gun is very well made with a nice polish on the metal parts, and a deep, beautiful blueing job on the barrel, but, and trigger guard. The lock was left in the white. The wood is fairly plain but serviceable, and the checkering was well executed. The inletting of the buttplate could have been better, though. This specimen was well cared for, with only some wear on the buttplate where it rested on the ground while being loaded, and only a few handling marks on the wood.
My plans for this gun include small game, upland bird, and maybe even deer hunting. For deer I'll use a patched round ball. For shot, I plan to get a punch and make felt wads from the same felt I use to make wads for my percussion revolvers. (According to this article, felt wads perform better than card and fiber wads.)
Once I get the chance to try the gun out I'll post some more thoughts.
*Investarms makes the Lyman Great Plains Rifle, Lyman Trade Rifle, and Lyman Great Plains Pistol. They also make the Cabela's Traditional Hawken, one of which I have.