There was a transition in the damascus pattern from the higher grade Lifters to the Top Action Hammerguns introduced in 1882. The c. mid-1870s Quality 2 through Quality 5 Lifters had, for the most part, the same 3 Iron 'Oxford' barrel, likely of British origin.
Examples are here
http://www.picturetrail.com/sfx/album/view/19406549
Destry once posted a pic of a BH stamped 'DD'. P. 511 of "The Parker Story", Figure 12.13, shows the barrel flats of a D-Grade (Quality 3) hammer gun SN 96343, made in 1900, with the DD stamp.