I'm cross-eyed from looking at patterns, but this is the only one I could find with a similar anomaly.
Charles Lancaster refinished ('browned') by Craig Smith with 4 Rod 'Oxford' right barrel, and 4 Rod 'Finest' Oxford left



No idea if this was a salesman's pattern demonstration gun, or another oops, but there is a consistent more darkly colored band at the breech end straight ribband edge welds.

This is the usual Parker Dam3 refinished by Dale Edmonds


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