Once saw a collectors byf 43 that had indications of being clamped in one of these... IIRC, there was compression of wood, and some rubber round shadow left on the buttplate...
Loved those in my Kubel and Kommandeurwagen.. Interesting factoid,..The one pictured is the type 2 design and the type one can be found in the Austrian Pinzgauers! I helped convert 6 M412s for Redbull and was surprised when I saw them. As Amberg pointed out above.