Upper Receiver alone can fire!

[Vlim]

To make matters worse, a procedure that enabled the German police to demonstrate this behaviour to cadets was described in Schmitt's 'Waffentechnisches Unterrichtsbuch für den Polizeibeamten' (police weapons training manual).

In the book he describes a fixture, consisting of a wooden board, a wooden end piece and four nails that help to keep the upper part in place.