Heinrich Krieghoff, etal. left town to be relocated probably in late 1945. That along with the fact that tube makers usually used script or Fraktur letters on the tubes and Heinrich usually had an overlapping "HK". So I'd guess barrel maker Hugo Kirchner. That "H" on the crossbar still makes me conjure up Brothers Helfricht.

Geno:
Is the tube pic with "HK"/"KH" from the same longarm as the receiver with the "AG" stamp?

Kind Regards,

Raimey
rse