Top gunmakers have gone over to state of the art CNC and EDM machines, check out the Purdey, Westley Richards and Holland videos for confirmation.
And after they are done with the space age machines they resort to 16the century tinpot technology to fix useless ribs.
Alex Martin had the right idea, do away with all ribs. His ribless guns were built by Powell and as one of the Powells wrote, it saved a quarter of a pound from the muzzle end of the guns. Ribless doubles have no inaccessible nooks for rust to work unseen.
A ribless sxs is hideous. Next in line would be one with a swamped rib. Aesthetics don't matter to some, but only some odd functionality advantage. These shooters are who these guns, without ribs or swamped ribs, were intended for.
JR
