I took a punt on this one, in the hope it held an early in-house MST auto...
The style is mid 50s and a nice size at 33mm. I suspected it held an MST 420/421 which came in 1956.
What can I say, some days you get lucky...
An MST 411. It is not in Rolands database, and as far as I have been able to work out by a process of elimination, the MST410/411 is most likely Roamer's first rotor auto. It may even be their first inhouse automatic. This one is rose gold 17 Jewels. The 410 has a sub second, 411 sweep second.
Hence watch dates to the early 50s (pre 1956).
The balance is almost completely hidden.
The 410/411 seems to be pretty rare, I have not seen another for sale, and the only other I have found on the web is here (his dates are wrong BTW). CousinsUK also has the datasheet on-line. I am pretty happy to have found this one, and in such good condition.
While I am confident that it is Roamer's first rotor auto, I am not sure it if it is Roamer's first in-house auto, as I have seen a bumper - and one may be in the mail to me right now. However, my suspicion is that the bumper was not in-house - this is the one I missed out on the 'bay a long time ago:
Somehow it doesn't look very MST to me, so I suspect the one that is coming will also not be MST in house calibre. In any case, a bumper Roamer is worth having any day.
I am also happy because I just got given this 1961/66 movement catalogue: