Hi,
In that case, I'm sure you will enjoy this image.
It's the Mauser rifle testing range in 1913.
I also own a 1912 copy of the instructions on construction of firing ranges, including build plans, dimensions, etc...
It's called the 'Atlas zur Schiessstands-ordnung' and was published by Ernst Siegfried Mittler und Sohn from Berlin. (D.V.E. nr. 304).
Also, I read that artillery/LP08 stocks were used by testers in order to get a steadier shot when testing normal P08's.