That's a good point, Ted. I had an overbored Sauer 20 (A&F import from the 30's) that came fairly close to .630. Correctly stamped 19, so the overbore came as no surprise. And I currently have a Francotte 20 that's stamped 15.9, and the bores check out. Agree with you and Miller that it's more likely to be a 20 than a 16.