There were several Douglass ( two ss"s) and Douglas family members who made guns in Huntingdon. From my limited experience the stock architecture and abundant similar styled inlays (furniture) and to some extent engraving style are similar among many gunmakers. Please refer to Whisker's book for a large pictorial collection of other makers from the area:" Gunsmiths of Bedford, Fulton, Huntingdon & Somerset Counties" that easily allows one to compare. The Museum on this site has many examples of Kopp guns, as you know, and a few other makers from that area.
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