The Omega Vintage Database indicates the cal 344 was COSC. Were all cal 344 chronometre grade or were they made in both non-chronometre and chronometre versions? I am have seen hundreds of watches in the cal 35X series, but I am not very familiar with this cal.
Interesting. The OVD often lists the cal 342 and 344 in sequence, with the 344 as COSC. However, I have found several examples of cal 344 on eBay, and so far none of them have been chronometer rated. It may be, that as with cal 354, some were and some were not
I have a 344 powered 1953 Seamaster that is not certified or marked as Chronometer. But I can tell you it keeps Chronometer grade time. If I recall correctly, the 344 was considered "Chronometer grade" but not certified. Omega referred to the 352, 333, 343 as "deluxe execution" chronometrer grade movements in comparison to the later caliber 354, 344 that using a swan neck regulation and standard finish wheels. The 354 was based off the 352, and the 344 was based off the 343, 28.10 JUB series The bulk of the 28.10 derivitive Chronometers were made between 1952 and 1955 . I'm sure I got something wrong here. Corrections welcome.