I just heard from the seller, who says that he subtracted 5 cm, which he attributes to the chamber length, from the overall length to arrive at the barrel length of 50 cm.

If that is his rationale, why he would not subtract 6.5 cm is a mystery to me. In any case, the barrels are 55 cm (22") long by my standards (and evidently Sempert & Krieghoff's, also).