I don't have any pictures this second but i will post them soon. Where is the forum for research? The gun is roughly 57 inches long. The barrels are 40 inches in length. Two barrels are side by side with the third in the center of the gun directly below the top two barrels. All three barrels are fired by a single cap. It is a muzzle loader style with the packing rod attached to the gun. It is marked down the center of the barrels with Gastinne Renette for the Paris Emperor (although that is the translation i believe from french). It also has the marking "Exhibition 1855". It has a mount for a tripod with a spring to take the shock of the recoil.
That IS unusual. The British and Americans had punt guns, huge single shotguns mounted in the bow of a small boat and meant to wipe out a whole flock of ducks at once. Maybe the French had rather fire off three barrels at once into the flock instead of one big one. But I don't know for sure. It will make a fascinating pictoral, though.