At first I thought I'd never heard of a double rifle made into a shotgun. Usually the other way round. But of course some DRs have had shotgun barrels made as additional barrels for them.

Then I remembered a "cape gun" owned by South Aussie elephant hunter John Dawkins. A Holland & Holland .450 NE side by side, one barrel bored out to .410 I think it was (?). I wonder why one barrel was bored out smooth? Damaged in some way? And converted. One day if the current owner still has it I must try to get good photos of it.