"Diana" refers to the Pieper patent monobloc barrels
"Original Diana" the tubes were inserted from the rear of the breech with a significant step. The guns usually had a steel breech with pattern welded tubes.
The "Modified Diana" the tube were inserted from the front with no step.
Pieper added other names to the "Diana" guns, and also used Royal Gun Works (and a bunch more) as a tradename
This is an old thread but fortunately most of the images remain
https://doublegunshop.com/forums/ubb...27249&page=all
With a close up of every mark on the barrel flats and just forward of the flats we could provide more information