Too, I wanted to stumble thru the marks on the underside of the pattern welded tubes, which are typical for the period.
On the underside of the left tube from top to botton:
Sauer Imperial Eagle
Wildmann with a Staff
CAL: 18.2
SE219R could be 2 or three independent stamps
Script lowercase g(I think)
Script K
Script H
Along with a couple of Gothic or Fraktur Js.
Interesting K, S and GD on the flat. Typical lowercase g on the lower rib(maybe 2?).
Repeated on the underside of the right tube along with an encircled Gothic R, which I have seen many, many times on German finished Belgian pattern welded tubes.
Cheers,
Raimey
rse