If the barrel is original and you can place the shroud profile in the same category as the registered version, I'd say early post war, say 1949 +/- 3 years.
Not sure if the 357 had a transitional period with long action hammer post war, but the factory is famous for putting batches of bits into servise out of sequence.
Non the less, an older 5 screw is a mighty fine thing to posses. While I wouldn't do it to my pre number 44 spl, it looks like the trigger has been smoothed out for less harsh double action on the finger, which should make it pretty slick feeling with the care and attention they paid to the internals back then. Enjoy!
R