My serial also ends in a B, but mine is about 6000 after yours serial # wise, the grips are different and mine does not have the lettering above the grips.
How are the grips different?
The models 1907 and 1915 use the same grips. The model 1917 has wider, trapezoidal grips and the grips have a screw through them to hold them to the frame (no screws are used anywhere in the 1907 or 1915).
The model 1915 also has the "SAVAGE" lettering above the left grip.
.380 model 1907 s/n range is approx B2000 - 15748B (1913-1920)
.380 model 1915 s/n range is approx 1000B - 13900B (1915-1917)
.380 model 1917 s/n range is approx 15749B - 29972B (1920-1928).
Bill
