Yes, I would imagine the gun was built from pre or early war production. Quality appears flawless, as I expect all prewar Sauers to be. Only a couple months after the proof mark the British and then Americans got serious about it. Amazingly, after all the incredible tonnage dropped on German industry, I believe peak Axis wartime production occurred in October of 1944!
However, the gun in question has a serial number of 311,xxx and I believe Sauer gave the tube sets numbers at the beginning of production. Be interesting to know when that was.
