Oh...1137...Ok (scratches chin and drifts back into the hazy days of apprenticeship and mis-spent youth).
So the barrel (and action?) material is a sulphurised free maching mild steel that could be heat treated if required, unlike normal mild steel.
So the Luger manufacturers of old had the benefits of an easy to machine yet relatively tough steel giving good surface finishes with the added benefit of it being able to be heat treated if needed, all in one type of steel.
Clever people those Germans.....
Cheers
<img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" />