Adding to Guy's comments, I think this would have started life as a 1939-1941 era British Service Revolver in .38 S&W (not .38 Special). It would not have had adjustable sights. Many of the BSRs and British Victory Models were released to the commercial market after WWII, and some British manufacturers (Parker-Hale, for example) converted some to .22 target revolvers. They sleeved the cylinder chambers and bore to accomplish this. For reasons which I do not understand, the replacement front sight was mounted further from the muzzle than the original service sight had been placed. Most by far of the BSR/Victory revolvers had five-inch barrels, but a few had them an inch longer, and this could be one of those.
Better photos and further information about actual caliber and serial number would be helpful, but I gather you may not be able to provide them.
As Guy pointed out, if S&W had manufactured this as a .22 the firing pin would have been mounted in the frame, not as a swiveling nose on the hammer. Though not good, the photos show the evidence that this was built as a center-fire revolver.
If built as a .22, it would have been marketed by S&W as a K-22 Outdoorsman's Revolver (or Outdoorsman). Collectors would not consider this a Pre-17 either because they do not use the "pre" terminology at all, or because they restrict its application to the postwar short-action revolvers to which the numerical model IDs became attached seven-10 years after the short action models were introduced.
The stocks do not appear to me to be original. They could have been replaced at the time the target sights were added and the chambering changed, or on some other occasion.
EDITED TO ADD: Your additional photos appeared while I was composing this. The format of the caliber marking is consistent with my suggestion about a postwar conversion by a British firearms company.
EDITED AGAIN: I may be wrong about the stocks. I know that some early BSRs had checking on the stocks, but I think they also would have had diamond reliefs around the screw escutcheon. My eyes can't see those in the photos.