I put in a very modest bid on the converted Horsley .410 single, originally a Horsley patent action Rook rifle.

It went for 4 times the low estimate.

I wonder what it would have made if still in its original calibre and configuration?

At the time it was converted Rook rifles were “on ticket” and relatively valueless. Still, converting it to a shotgun may have saved most of it from complete destruction.