Just saw this rifle this very morning. To say that it's buxom is an understatement. probably 1 3/4" thru the wrist, and 2 1/4 across the rear of the lock panels. Buttplate is at least 5" tall, and 2 1/4 wide. The barrel appears to be 1 1/4" wide at breech, and maybe 42"? Hard to tell, since it's all behind glass. It's fully as big or bigger than the Oerters.
The relief carving is incredibly good, stabbed, I presume, with some incised highlights. Just a total joy to the eye.
The patchbox thought occurred to me that it could have been added later. The carving on the wrist ahead of the finial is scrubbed off pretty hard, a long time ago, and the inlet of the patchbox finial is rather deep. There is no cutout in the buttplate for the door, nor any evidence of a slider, the door just butts up to the plate. Unusual lever mechanism to open the door. Maybe this was early, and popular mechanisms weren't fully developed yet.
The gun indeed poses more questions than it answers.
It's now installed in the large case with other guns, and will be there for the duration of the show. While the glass gets in the way of getting up close and personal, this is a show that will knock your socks off. Albrecht, Beck, Fordney, Fainot, Pannabecker, Dickert and a bunch of other heavy hitters are on display. Worth a trip from anywhere.