The 234 was produced from 1949 through 1974. The 234L (ejector) began production in 1950. The factory chamber length will be on the barrel flats in mm. I have the Robust book and it has an ad listing the chambers in 1971 as 70 mm or 2 3/4". I don't believe there is a serial number list existing. I have a 226 which was made between 1932 and 1940 with a serial number of 189xxx. Hundreds of thousands of Robusts were made in various grades. They were mail order guns in France. Gil