Hi
The serial number is 278811. The B in front of it on the barrel flat is simply an indication that the gun left the factory with a blue finish. This was put with the serial number only in that location. It isn't a prefix, since those were first used during WWII and thereafter on postwar guns.

The reason you don't see the serial number on the grip frame is that the stocks are covering it up. If you were to take them off, you would find the serial number there (unless it has been illegally removed). The serial number should also appear on the rear face of the cylinder, and a couple other places that are very difficult to see.

With that serial number, your .32 was probably made in 1917 although it might not have shipped until 1918. One cannot tell without getting a letter from the Historical Foundation.

The stocks are probably custom made. It seems possible they are heavily modified from S&W extension stocks of the period, since they do resemble the shape of those. But either way, they didn't come from the factory looking like that. They are interesting, however.

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Jack
SWCA #2475, SWHF #318