I'll look later tonight on a few post WWII examples but can you email or post a pic of the verbiage. You are correct though it should say "Spezial Gewehr Lauf Stahl" - Special Weapons Grade Tube/Barrel Steel. I'm puzzled by the "S.G.1" for now. The "1" in the "Q" is the top/outstanding quality mark. What's the name on the underside of the tubes, Simson?

Kind Regards,

Raimey
rse