Ron,
You got me thinking...
I rotated and slightly enlarged the image. You can clearly see the straight rear-end (where normally the stock lug is placed). It differs from examples I've seen pictured, including those in John Walters books.
Just saw some detail photo's of the 45 carabine, and the grip end appears to be of similar shape, but it lacks the small lug present on the carabine.
This picture shows a detail image of some 45 tails:
Carabine, 2nd Test, German Article
