I'm not sure that all (or any) 686's have chrome bores. I have three early 686 Onyx guns (with the black frame, steel grip cap, and Mobil Chokes) and I'm pretty sure that none of these have chrome bores. I also don't think I've ever seen a U.S.-spec 686 with fixed chokes that would need opening. I believe there were Euro-spec guns (S56E?) with fixed chokes. These look like 686's, as I recall. The BL-series guns also had fixed chokes, as I recall.