Bob, At one time I had a rifle signed A. Kunz. Nice box with one or two drums and crossed flags on it. Bethlehem star and a bone inlay on the cheek piece side. At that time a descendant of the Kunz family told me Adam was a brother of Jacob . He had obtained this information from a will.
Neat.
Jacob
did have a brother named Adam (1781-1865), the middle brother between gunmakers Jacob and Peter.
All I can find on Adam is that he lived in East Allentown, and became a relatively wealthy man. He was taxed for the luxuries of a carriage and gold later in life during the Civil War, and had net assets of $11,500. Pretty good for rural Allentown.
But isn't that back-action lock a little late for the builder to be Jacob's brother rather than his son? I'm not very knowledgeable on these rifles, but I don't recall ever seeing a back-action flintlock. It also looks like it could be a patent breech from here. Another later innovation.
Unlike the Newhards and Molls, the Kuntz family line is small, with few family histories out there to confirm various census and tax records. Add a large number of later German immigrants named Kuntz during the migration west, and it's harder to track them.