Some further information. I spoke to the dealer today. The rifle did not come from the estate of an Alfred Ronstadt. It was consigned by the estate manager for the last of three brothers. They all collected guns for 70 years, and the last survivor inherited the lot. (Apparently something like 600 guns.)

Not long ago the estate manager held a garage sale and sold piles and piles of gun and gunsmithing tools and accessories for derisory prices. The gun shop managed to save the last 10%, and they are looking for that missing buttplate.

They told me that the elderly surviving brother said that this rifle was very special. They are going to put him in touch with me to talk about its provenance.