Another thing of note.......the "S" inpsection stamp, such as the one on your barrel, had stopped being used in the earlier period of S&W M1917 production. Thus your example had it's barrel built and inspected in the WWI era and laid around unserialized for a number of years until built into a commercial model at a later time.
Was there an "S" stamp on the rear face of the cylinder as well?
We really need more pics. If your frame truly is a WWI era U.S. contract frame, with proper inspection markings, the would be somewhat of an unusual item having the later era commercial rear sight style (added).
I'd love to see all of it's inspector stamps, whether they be an early production "S" or later production eagle head/S-number style.
Mr. Jinks has said that S&W didn't stamp 'US Army Model 1917', and a circle with GHS inspector or the flaming bomb on all guns until after the Govt. took control of S&W in Jan 1918 because of Govt. dissatisfaction with S&W's production speed of the M1917.
Most early WWI 1917s are marked "GHS" in a circle, (Gilbert H. Stewart), Gov't inspector, left side frame up near the hammer: serial number approximate range 1 to at least 43894. During this period just an S inspector stamp for Stewart is used w/o eagle head or # following the S; found on cyl, under barrel and maybe frame. Note: there's also a GHD, Guy H. Drewry inspector from 1930-1957 (with various increasing ranks in front of his name), who was in charge of the Hartford Ordnance District and under whose authority and name, ordnance contractors stationed at the S&W factory inspected guns both for Lend-lease and for ASP (Army Supply Program) contracts.
Later guns are marked with a flaming bomb on upper rear left side of frame, beginning c. #42000 until deleted April 1918. So we see an apparent overlap of the two stamps being used. But most likely the bomb stamped guns numbered below 43894 were produced/shipped after the end of the GHS stamp use.
The April 1918 date is likely correct. But as usual with Smiths there are anomalies caused by the complete lack of Smith's serial # chronological correlation to their manufacturing and shipping dates. Therefore we find frames stamped with the flaming bomb most likely before April 1918, but not shipped till later, as late as the end of 1918 and mixed in with guns w/o the bomb stamp.
Later war time produced guns are inspector stamped in various locations with an eagle head over an "S" followed by a number like S1, S2, S3, S4, S6, S9, S24, S27, S34, etc., in several places from April 1918 to war's end: an early example is s/n 111XXX.
More details of inspector stamping:
http://smith-wessonforum.com/s-w-hand-ejectors-1896-1961/606106-stamp-1917-frame.html#post140614710