Keßler had a formidable shop as far as I know, and well had the means to have a frame filer & action mechanic. But the concern would have had to sourced forgings from Sauer but don't forget that F.W. & Bernhard Keßler were principals in Römerwerk/Rhömerwerke, where a lot of heavy lifting occurred. So with the highest probability, F.W. / Bernhard Keßler sourced a frame forging or filed frame from Rhömerwerke.
In 1925 there was some sorting with the F.W. Keßler concern and the heirs became unified or similar. Not sure exactly who all they were??
Hochachtungsvoll,
Raimey
rse