Over-mag shotgun

Many people, when using only one barrel of a double-barrel shotgun, prefer to use the lower barrel because its lower bore axis reduces muzzle rise. Indeed, some single barrels designed for installation on double-barrel shotguns have the functional barrel in the lower position and unbored metal with an extra-tall comb in the upper position.

I would propose that similar benefits could be achieved in repeating (pump or semi) shotguns if the magazine tube were locaded on top and the barrel were underneath. This would require some changes to the mechanism, but nothing severe. A probable advantage would be that the ejection port could be aimed straight downward (some Ithaca shotguns conveniently eject downward, but they have the magazine on the bottom).

The only difficulty I can see with such a design would be convincing the Treasury Secretary that it was "suitable for sporting purposes" in compliance with the National Firearms Act of 1934. Absent such determination, such firearms could only be sold to the general public in 28 gauge (fixed choke) or .410. I don't see why the guns should be considered "non-sporting", given that the goal would be to improve performance when trap-shooting or wing-shooting, but the BATF isn't known for niceness.