I agree with Jan Balcars hypotesis. The Holzatrappe is for a soldiers service, when he don�´t needs really a real pistol in his holster. It is much mor comfortable and not so heavy at all, and he don�´t have to watch his gun all the time as it would be with a real Luger.
Why the Waffenmeiser have had that pice of wood? probably to know how to duplicate it?
here is a picture of one I purchased recently - much more different and probably not in military use - but interesting...

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