When you are at Arnsberg ask your guide to ring Walther at Ulm and arrange a tour of the Walther factory, Ulm is not far from Arnsberg. You will see how the actual firearms are produced. My wife and I spent a morning there a month ago, it is absolutely fantastic, we had a full factory tour, we are serious target shooters and we also had the services of the tech dept to discuss new target rifles. The highspot is the museum which is absalutely magical.
It is a high security site, but if circumstances are right they will probably grant you a tour especially if you get your Arnsberg hosts to book it.
Robin