Please forgive the dumb question, as I have zero experience shooting in Argentina, nor am I ever likely to have any (if it has feathers and my dogs don’t point it, I can’t be bothered to shoot it). Nonetheless, the question of the ultimate high endurance gun is interesting.
Why wouldn’t a 12 gauge target O/U stocked to fit with 20 or 28 gauge bbls be the ideal Argentine gun? For example, a full-framed K-80 with 28 gauge bbls (not tubes – those would seem a bit clumsy) is utterly reliable and one could shoot such a gun all day long without discomfort from recoil. There is no lack of old K-80 four bbl sets to build into an Argentine gun. Of course, a Perazzi or similar gun would serve the same purpose. Is the problem managing a 9 pound gun for 1,000 rounds in a day?