My first though looking at 520Fan's pictures is that the holes along the top of the barrel rib were for the attachment of a weight. After more study, they appear to allow moving the front sight to change sight radius. Neat!
I posted this once before; this is my H&R/Roper. On page 213 of Pistol and Revolver Shooting, Roper shows one identical except for barrel length. He attributes the European-style modification to George Hyde of New York. George Hyde is better known as the designer of the M3 "grease gun" submachine gun.
Bob
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