Hard to see the proofmarks, but I think I see 16-70, which would be 2 3/4". And that's further indication the gun could not date from 1920-21, because that proofmark wasn't used until 1924.

Bob Beach just did great research work for me on an A&F-imported Sauer from 1936. I highly recommend the G&H research service to anyone with a gun imported by VL&D, VL&A, or A&F that Bob can connect to a serial number in their record books.