A double barrel shotgun, with a rifle barrel under and between the shotgun barrels is known as a drilling.
The dri part is derived from Zie German drei, or three.
If you add another rifle barrel above and between the shotgun barrels it's a vierling.
The vier part is derived from fear, or four.
It makes me wonder why a combination gun in German isn't zwilling (derived from zwei or two) or something like that. Near as I can tell, Bockbüchsflinte is what Zie Germans called it.
From making 1/35 scale tank models I know that there's a couple of twin AA guns called zwilling, but they're hard on the meat for hunting.
With pictures! I've had that gif saved for years and years, no idea who made it or where it came from.
That chart makes me wonder if there's another special name for a two-barreled gun with the rifle barrel on top.