Great photography and wonderful that Jud was able to obtain permission to both photograph the piece and post photos publicly. Spectacular!
The concept of it being a long-barreled "jaeger" is somewhat simplistic (not trying to be sarcastic here, just trying to convey a point) as while we frequently think of German rifles being short stubby little things - and of course some were - others were longer. Take a spin through a number of differing European auction catalogs and you will see a very large variety of rifles originating in the German-speaking lands with a fairly wide range of barrel lengths. This is not particularly out of the ordinary, imho, although the longer barreled pieces tended more often than not to be smoothbores. Chris Immel could surely comment more informatively here, if he still exists…
I do not think this rifle as it exists was present for the Walking Purchase, the decorative forms do not seem to fit the timeframe - carving, lock engraving, lock style etc.
The trigger guard is of a style and form which has materialized on a small handful of other pieces in minor variations. I suspect that the guard at the least (and of course the lock and barrel, but I'm speaking only of brassware here) was either an import piece that was apparently part of a 'lot' of similar pieces, or else was cast here - perhaps in Philadelphia? - to a common pattern. Moravian casting at Bethlehem? I don't know, this still seems unclear to me.
The buttplate presents something of a question. The heel is filled with lead. Is this a repair? Obviously it has worn through, but this is to be expected because the brass of the whole butt piece is extremely thin. There are Hudson River pieces which can be found with lead filling the bulbous butt heel, and these are pieces which have not been repaired. The lead apparently was put there at construction in order to provide support and to ease inletting, i.e. no need to fill the heel with complex wood inletting for support. There is substantial scarring around the lower portion of the bulbous heel segment in particular which *looks like* the heel was being hammered into a swage depression. Part of a repair? Original forming from sheet? Nobody knows. It does not photograph well at all, but in-hand it is very evident.
I also firmly believe, although I think I'm in a serious minority here, that the barrel is installed upside down. I do think the barrel at least saw prior use, and I think that what we currently see as the top of the barrel was originally the underside of the barrel in another stock. I'll leave it at that since I can not point to photographic evidence, only my own observations when I was permitted the opportunity to handle it at the MM many years ago.
ANYONE seriously interested in early American history needs to spend at least a full day at the Mercer Museum before they croak.