WOW...a neat idea that appears to have become a reality. To expand on this idea a bit, a few years back a local agricultural paper had an article in it about a box lock gun with four barrels. The gun in this article said that it was made in Ferlach, Austria by a small arms builder and could be had with either all the barrels in the same caliber/gauge or with each barrel a different caliber/gauge, including rimfire cartridges.
Very OLD shotgun. Not a practical hunting firearm anyway. The Drilling had two shotgun barrel in the usual S&S configuration with the third rifle barrel under the other two there are a few made the other way as well. This had the advantage of only needing one gun in field for both birds and deer/ meat..
Hollenbeck Gun Co. 1901-1905
Three Barrel Gun Co. 1905-1908
Royal Gun Co. 1909-1910
All three were the same company, there were several other 3 barrel gun makers involved about the same time. Multi Barrel guns ( other than a double ) never really caught on in the states. They had a purpose in Europe with overlapping hunting seasons but they have always been an oddity in North America. Other than just having something different I can't see much use for a three barrel shotgun. Now a over under rifle /shotgun combo such as the Stevens'Savage, with a small caliber rifle on top and a 20 gauge on the bottom always seemed like a neat ideal, if you liked single barrel shotguns. Just my way of thinking.
One of the problems with a combo gun is that for years many of the States didn't allow one to be in possesion of a rifle (or handgun) while deer hunting in a shotgun only State.
I've owned a Savage 24 for many years, but I couldn't use it to deer hunt back in the day because of this.
So interest was low because the perceived advantage wasn't there.