the 'Krupp-Laufstahl' with bullets in your photo of the Robert Schüler and also the mark behind it is identical on my gun
(no Krupp Rings)
Also, in your photo there is what looks like a capital letter'D' on the center barrel behind the lug.
This letter 'D' is also on my gun
I have taken this as an inspection mark, but am not certain.
Does this mean that the barrels at least have gone through the same workshop?

just behind the date stamp




Best regards
Günter
NRA Life 1974