Bit of a thought puzzle for me also, Ted. In fact, I think I've asked the same question regarding specific intended fodder for "tight" bores in European 12s (Merkel and Manufrance as examples) and got the usual advice of "pattern to find out what looks good on paper". Maybe 4 thou under nominal isn't that big a deal but you do begin to wonder at .719". I think it's beyond doubt that there's a difference of "fit" of a plastic wad in bores of different diameter and a corresponding difference in produced pressure due to friction and assured complete obturational gas seal in the tighter bores. I have had stuck wads a few times and carry a wad knocker (5" long chunk of brass bar stock)which will remove a wad obstruction on a typical overbore (.740 or so) target gun. It wouldn't budge one in the bore of an old .723" bored Beretta and I had to resort to the range rod. I've never stuck a wad in a 12 ga. Moneymaker barrel bored .789".
Back from the anecdotal to the question at hand, I also would like to know if there is "intention" in boring tight and an optimum design load in terms of components for such guns. Bore leading aside, if I knew the intended fiber wad load for my Merkel 200 (problem also compounded by choking differential in one barrel of over .050" below bore diameter), that's what I would be loading for work involving flying things other than the bitumen sort. CIP pressure limits I understand. The thinking (or lack thereof)by which these guns got "grandfathered" into the plastic wad and shotcup era I don't understand.
jack
