[absolootezer0]

If you install a rifled barrel in a 12-guage shotgun, then I think you do have a 12-guage rifle.

with a slug barrel, its still considered a shotgun as it is still designed to use plastic shotshells.
else, it would be a .729 calibre rifle, which too big. i believe it would have to be registered as a DD.

[elmer fudd]

with a slug barrel, its still considered a shotgun as it is still designed to use plastic shotshells. else, it would be a .729 calibre rifle, which too big. i believe it would have to be registered as a DD.

Not if it's deemed to have sporting purposes. It's not well known, but any shotgun with a bore over .5" can be deemed a destructive device at the government's will. That's what happened with the Striker/Streetsweeper/Jackhammer shotguns. There was never any legislation or EO to outlaw them. The Secretary of the Treasury simply declared that they had no sporting purpose and were henceforth considered destructive devices.

[kitchen]

There is a 12 gauge rifle out there, for all you recoil junkies - the 12 Gauge from Hell. The designer addressed the DD registration by using a rimmed case and a chamber that would accept 12 gauge shot shells.