"That is where most double rifles went after they left the makers. This re-boreing, and sometimes re-regulating, was quicker, and more cost effective than making complete new barrel sets so the customer would have his rifle back quickly, and at less cost."

A lot of H&H Doubles were not rebored but rebarreled to 500/465. Just look at the "large" number of 500/465 Hollands around with new barrels.