Werndl 11.15x42R 11mm scharfe Patrone M.67

[Patrick Chadwick]

That should be fairly simple, by shortening, annealing and reforming the usual Mauser 11.15x60R case.
I think Patrick Villiers has some experience with this for the Werndl. I have done it for the 11.15x38R .
A straightforward exercise - if you have the dies.

However, don't rush out and buy dies etc. until you actually have the Werndl in your hands and can check the chambering.

The tabatiere-style construction of the Werndl makes it awkard to make a chamber casting in the usual manner.
As you are in France, the simplest way to check the proper case size is to take an 8x50R Lebel case, ink it over with a felt pen, allow to dry for several seconds, then insert the Lebel case into the Werndl chamber and twiddle it round and round.
When you remove the case there will be a bright line rubbed through the ink.
Measure the diameter of the case at this line.

If you do this carefully, the method is quite sensitive enough to show you whether the proper case diameter is
(approx.) 13 mm = 11.15x42R or
(approx.) 14 mm =11x58R.