Your gun is interesting Hal. It is a Pieper Diana Breech. Here is a Pieper J. Manton & Co. Modified Diana with another (odd) breech treatment

[Linked Image from photos.smugmug.com]

It should be an early gun, but the proof marks date it to 1910-1920. Pieper was known to use 'D.C.' for some reason.
The R barrel is Cylinder with a bore of 18.2 mm = .717". The L muzzle constriction is 17.6 mm = .693" = .024" or IM
Looks like a 'gunsmith' pounded on the barrel lug to tighten the FE?
And the L firing pin may be a nail?

Note Dave's Sears ad lists "Royal Damascus Finish" meaning Faux Damascus, likely décalcomanie over decarbonized or fluid steel; Pieper was reported to use Siemen-Martin from Cockerill which was good stuff.
Your gun looks to have the same process.

This is a T. Parker in the 1895 Montgomery Ward catalog with "Imitation Damascus"

[Linked Image from photos.smugmug.com]

T. Barker in the 1899 Sears catalog with "Royal Damascus Finish"

[Linked Image from photos.smugmug.com]

T. Barker in the 1902 Sears catalog but the illustration clearly says T. Parker. It also has "Royal Damascus Finish" over Sears' tradename Wilson's steel which was probably decarbonized steel

[Linked Image from photos.smugmug.com]

Tomas Barker in the 1902 Sears catalog with "Imitation Twist"

[Linked Image from photos.smugmug.com]

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