On a completely different tack, and looking at the context in Dollaczek (page 87 refers to the mortar as "der Kernpeiss in Osterwitz"), there is a district called Osterwitz in Austria and about 35 kilometres away, there is a place called Kernpeis, which has a quarry (Kernpeis-Steinbruch).

The mortars mentioned by Dollaczek fired stone shot, which in this case may have come from the quarry at Kernpeis, which may have given the gun its name.

Of course all purely conjecture on my part.