The picture in "The Big Shots" shows Prince Victor in action,assisted by two loaders, with a cartridge boy standing back. Also shown is a separate picture of Victor and a lady seated,waiting for a pheasant drive to begin. The same book, page 44, shows Lord de Gray using a trio of guns.
As a matter of interest, some English gunmakers,including H&H have produced sets of four and more guns, often in different gauges.

Roy Hebbes