That is simply an outstanding and ultra-desirable original pre-war .22 Kit Gun. I found the exact identical model, ser. #532XXX, exhibiting extended square butt regulation Police type stocks and a patridge front sight, about 5 years ago at a gun store in Lancaster County PA. Owner didnt realize it was a true pre-war kit gun and priced it substantially below market value. Yours is nicer than mine which retains approx. 85% original bright blue. Just happened across another identical 4" model last week retaining only 30-40% weak blue, with serial no. 276XXX. This had to be a factory converted 6" Beakert model as the serial is way low being built substantially before the actual production of Kit Guns by S&W in 1936. Left that one slide. Anyhow, congrats on a great catch. Enjoy and best regards.