To complete the information about Model 21 20 gauge 3" chamber markings, this picture shows the barrel flats and water table of a 'Custom Grade' Model 21 20 gauge 3" Magnum built in the Custom Shop in 1968. The barrels have no markings other than "Custom Built by Winchester' on the Rib.
The gun is a 26" barrel gun choked IC/Mod, so not a duck gun but most likely ordered with pheasants in mind. Schwings book lists 519 20 gauges made in the Custom Shop but does not indicate how many were 3" Magnums so a total count of Winchester Model 21's 20 gauge 3" Magnums eludes me!-Dick
