That's a nice and very representative J.H. Johnston rifle. He worked in Waynesboro, PA. He was the father of the James Johnston who started and ran Great Western Gun Works in Pittsburgh, PA. I have a similar one and it is carved in the same basic pattern. His patchboxes were always similar and pleasing to my eye, at least. There is a period newspaper interview of J.H. Johnston published in the book "Gunsmiths of Pen-Mar-VA 1790-1840" by William S. Bowers. This book is pretty hard to find these days.
Art DeCamp