Maps,
I beg to differ. You are correct that the port is forward of the magazine (STG series) on the Gustloff designed self loading Volkssturmgewehr or aka the model 507.
However the port is directly above the magazine (G/K43 series) on the Walther designed bolt action VG1.
Which is the rifle I stated in my first post.
Samster,
I am big enough to admit that I now believe I was hasty in my guess and wrong.
It is not a VG1. Maybe I was just seeing what I wanted to see. Lesson learned.
Good thing you didn't have a BIN!
Still hoping to read more details.
Good luck with it, JT