By field rib I expect you are talking about solid rib. Those did end in the 50's. I have a soft spot for Browning with two triggers and solid ribs. Those have all been made in the early 1950's or older, like pre WWII. Many were the single-double trigger configurations which were converted to standard double triggers by Brownings. Never figure out if they just did not have parts to repair them as a single-double or never got many of them operating properly and just automatically converted any returned for service.
