Royal Gun Works was a Pieper tradename Gene, for Simmons Hdw., St. Louis
The Ptd. refers to the Modified Diana Pieper Patent

Here's a nice one with steel breech and "Washington" tubes
https://www.gunsinternational.com/g...fied-diana-12-gauge.cfm?gun_id=101363054

It does not carry Nitro Proof, but that is not uncommon on guns made for export to the U.S. Nitro Proof was not mandatory until 1924, and there was an additional Proof House charge.

I don't see a lettre annale so it was made 1910 to 1921 by La société anonyme des Anciens Etablissements Pieper - probably pre-WWI

Much earlier Simmons catalog

[Linked Image from photos.smugmug.com]

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