I think the lack of weight scares the most ones of. A couple of .600 barrels on a 12 gauge with a decent profile and lenght would land around 5-5,5kg. But you are right someone should make the attemt, and perhaps someone did but he/she arent around to tell the tale.

With a new well fitted set of barrels on a merkel 12 gauge frame it should be able to take the force of the cartridge, now how many times you could fire it untill it came off face thats another question, but at that weight i think most one wouldnt go shooting it much. Damn this gets me thinking for sure, if it hasent been done before, perhaps one could be the first for once.